Integrins and mechanotransduction of the vascular myogenic response

This review summarizes what is currently known about the role of integrins in the vascular myogenic response. The myogenic response is the rapid and maintained constriction of a blood vessel in response to pressure elevation. A role for integrins in this process has been suggested because these molecules form an important mechanical link between the extracellular matrix and the vascular smooth muscle cytoskeleton. We briefly summarize evidence for a general role of integrins in mechanotransduction. We then describe the integrin subunit combinations known to exist in smooth muscle and the vascular wall matrix proteins that may interact with these integrins. We then discuss the effects of integrin-specific peptides and antibodies on vascular tone and on calcium entry mechanisms in vascular smooth muscle. Because integrin function is linked to the cytoskeleton, we discuss evidence for the role of the cytoskeleton in determining myogenic responsiveness. Finally, we analyze evidence that integrin-linked signaling pathways, such as those involving protein tyrosine phosphorylation cascades and mitogen-activated protein kinases, are required for myogenic tone.

Dependence of the yield of DNA double-strand breaks in Chinese hamster V79-4 cells on the photon energy of ultrasoft X rays

Induction of DNA DSBs by low-LET radiations reflects clustered damage produced predominantly by low-energy, secondary electron "track ends". Cell inactivation and induction of DSBs and their rejoining, assayed using pulsed-field gel electrophoresis, were determined in Chinese hamster V79-4 cells irradiated as a monolayer with characteristic carbon K-shell (CK) (0.28 keV), aluminum K-shell (AlK) (1.49 keV), and titanium K-shell (TiK) (4.55 keV) ultrasoft X rays under aerobic and anaerobic conditions. Relative to (60)Co gamma rays, the relative biological effectiveness (RBE) for cell inactivation at 10% survival and for induction of DSBs increases as the photon energy of the ultrasoft X rays decreases. The RBE values for cell inactivation and for induction of DSBs by CK ultrasoft X rays are 2.8 +/- 0.3 and 2.7 +/- 0.3, respectively, and by TiK ultrasoft X rays are 1.5 +/- 0.1 and 1.4 +/- 0.1, respectively. Oxygen enhancement ratios (OERs) of approximately 2 for cell inactivation and induction of DSBs by ultrasoft X rays are independent of the photon energy. The time scale for rejoining of DNA DSBs is similar for both ultrasoft X rays and 60Co gamma rays. From the size distribution of small DNA fragments down to 0.48 kbp, we concluded that DSBs are induced randomly by CK and AlK ultrasoft X rays. Therefore, ultrasoft X rays are more efficient per unit dose than gamma radiation at inducing DNA DSBs, the yield of which increases with decreasing photon energy.

Ethnicity and seizure threshold

1. Seizure threshold is an important variable in modern ECT treatment planning. To date, age, gender, and electrode placement have been used to predict seizure threshold, but the potential impact of ethnicity has received little attention. 2. In a retrospective pilot study of patients who received ECT, 20 pairs of first admission, right unilateral-treated, age- and sex-matched black and white patients were compared. 3. Black patients had higher seizure thresholds and were more likely to require restimulation, despite the finding that they were more likely to have been receiving concomitant medications which lower seizure threshold. However, ethnicity was confounded with variations in ECT dose titration, which were the strongest predictor of seizure threshold. 4. There were no differences in seizure length. Further study is necessary to confirm the impact of ethnicity on seizure threshold.

Temporal aspects of Ca(2+) and myosin phosphorylation during myogenic and norepinephrine-induced arteriolar constriction

Previous studies demonstrated that maintenance of steady-state myogenic tone requires Ca(2+)-dependent myosin phosphorylation. The present studies furthered these observations by examining temporal relationships among Ca(2+), myosin phosphorylation and vessel diameter during acute increases in intraluminal pressure and norepinephrine stimulation. Rat cremaster muscle arterioles were cannulated and loaded with the Ca(2+)-sensitive indicator fura-2. The extent of myosin phosphorylation was measured using two-dimensional gel electrophoresis. Acute increases in intraluminal pressure caused a biphasic increase in intracellular Ca(2+) ([Ca(2+)](i)), characterized by a transient peak followed by a decline to a steady-state level which remained significantly higher than control values. Peak [Ca(2+)](i) was significantly related to vessel distension and increased with the change in wall tension. Increased intraluminal pressure resulted in a monophasic increase in myosin phosphorylation that was significantly correlated with instantaneous wall tension. In general, norepinephrine induced larger [Ca(2+)](i) transients and a biphasic myosin phosphorylation pattern. The results demonstrate: (a) major roles for Ca(2+) and myosin phosphorylation in arteriolar myogenic and norepinephrine-induced responses; (b) that changes in Ca(2+) and phosphorylation during a myogenic response are related to changes in wall tension, and (c) differences in Ca(2+) and phosphorylation patterns between the two modes of contraction reflect possible differences in underlying signaling mechanisms. The data further emphasize that spontaneous arteriolar tone represents a state of maintained smooth muscle activation that requires increases in [Ca(2+)](i) and myosin light-chain phosphorylation.

Tissue specificity in rat peripheral nerve regeneration through combined skeletal muscle and vein conduit grafts

Diffusible factors from the distal stumps of transected peripheral nerves exert a neurotropic effect on regenerating nerves in vivo (specificity). This morphological study was designed to investigate the existence of tissue specificity in peripheral nerve fiber regeneration through a graft of vein filled with fresh skeletal muscle. This tubulization technique demonstrated experimental and clinical results similar to those obtained with traditional autologous nerve grafts. Specifically, we used Y-shaped grafts to assess the orientation pattern of regenerating axons in the distal stump tissue. Animal models were divided into four experimental groups. The proximal part of the Y-shaped conduit was sutured to a severed tibial nerve in all experiments. The two distal stumps were sutured to different targets: group A to two intact nerves (tibial and peroneal), group B to an intact nerve and an unvascularized tendon, group C to an intact nerve and a vascularized tendon, and group D to a nerve graft and an unvascularized tendon. Morphological evaluation by light and electron microscopy was conducted in the distal forks of the Y-shaped tube. Data showed that almost all regenerating nerve fibers spontaneously oriented towards the nerve tissue (attached or not to the peripheral innervation field), showing a good morphological pattern of regeneration in both the early and late phases of regeneration. When the distal choice was represented by a tendon (vascularized or not), very few nerve fibers were detected in the corresponding distal fork of the Y-shaped graft. These results show that, using the muscle-vein-combined grafting technique, regenerating axons are able to correctly grow and orientate within the basement membranes of the graft guided by the neurotropic lure of the distal nerve stump.

Infection of pigs by Aujeszky's disease virus via the breath of intranasally inoculated pigs

Aujeszky's disease is a worldwide problem in the pig industry. In this experiment, four pigs chosen to act as shedder pigs were intranasally infected with Aujeszky's disease virus. Next, on three consecutive days, eight recipient pigs were exposed to the breath of a pair of shedder pigs via a mask-to-mask module. Except for the virtual absence of CNS signs, shedder pigs expressed clinical signs that were similar to pigs infected naturally or experimentally. Only mild respiratory signs occurred in recipient pigs, but all were infected by aerosols of Aujeszky's disease virus as evidenced by seroconversion. The pig is a much more sensitive indicator of airborne virions than our aerosol collection methods. We conclude that the mild respiratory disease acquired by the aerogenous route in recipient pigs is an easily managed model for studying the transmission of airborne respiratory infections and the immune responses to this type of infection.

Pressure related apoptosis in neuronal cell lines

Pressure is a crucial component of the cellular environment, and can lead to pathology if it varies beyond its normal range. The increased intra-ocular pressures in acute glaucoma are associated with the loss of neurons by apoptosis. Little is known regarding the interaction between pressure and apoptosis at the level of the cell. The model developed in this study examines the effects of elevated ambient hydrostatic pressure directly upon cultured neuronal lines. Conditions were selected to be within physiological limits: 100 mmHg over and above atmospheric pressure for a period of 2 hr, as seen clinically in acute glaucoma. This system can be used to investigate pressure relatively independently of other variables. Neuronal cell line cultures (B35 and PC12) were subjected to pressure conditions in specially designed pressure chambers. Controls were treated identically, except for the application of pressure, and positive controls were treated with a known apoptotic stimulus. Apoptosis was detected by cell morphology changes and by 2 specific apoptotic markers: TUNEL (Terminal transferase dUTP Nick-End Labeling) and Annexin V. These fluorescent markers were detected and quantified by automated Laser Scanning Cytometry. All techniques showed that increased pressure was associated with a greater level of apoptosis compared to equivalent controls. Our results suggest that pressure alone may act as a stimulus for apoptosis in neuronal cell cultures. This raises the possibility of a more direct relationship at the cellular level between pressure and neuronal loss.

Techniques used by a group of United Kingdom-based dental practitioners during the provision of indirect tooth-coloured restorations

A number of techniques involving the use of various instruments, brushes and devices have been described for the removal of excess luting material and subsequent finishing around the margins of indirect tooth-coloured restorations. There is little information available on the clinical techniques employed by UK dental practitioners in the placement of these restorations, or on the effectiveness of these techniques. A questionnaire was designed to elicit such information. This was distributed to 500 UK-based dental practitioners. A total of 301 practitioners returned completed questionnaires, giving a response rate of 60%. The results indicated that 88% of the respondents routinely provided porcelain veneers for their patients, with 94% of these respondents indicating that they routinely prepared teeth during the provision of such restorations. A light-cured resin composite luting material was used by 29% of the respondents in placement of veneers, while 69% used a dual cured composite. Excess uncured luting material was removed by a number of methods and a variety of methods were used by respondents to finish the margins of the veneers after placement. Of the respondents 68% indicated that they routinely provided tooth-coloured inlays and onlays, with 89% indicating that they routinely used a dentine bonding system when luting their indirect tooth-coloured restorations. It is concluded that a high proportion of the practitioners surveyed were providing porcelain veneers and tooth-coloured inlays and that a wide variety of materials and finishing techniques were being used.

Use of radiography, computed tomography and magnetic resonance imaging for evaluation of navicular syndrome in the horse

Radiographic evaluation of navicular syndrome is problematic because of its inconsistent correlation with clinical signs. Scintigraphy often yields false positive and false negative results and diagnostic ultrasound is of limited value. Therefore, we assessed the use of computed tomography and magnetic resonance imaging in a horse with clinical and radiographic signs of navicular syndrome. Cadaver specimens were examined with spiral computed tomographic and high-field magnetic resonance scanners and images were correlated with pathologic findings. Radiographic changes consisted of bony remodeling, which included altered synovial fossae, increased medullary opacity, cyst formation and shape change. These osseous changes were more striking and more numerous on computed tomographic and magnetic resonance images. They were most clearly defined with computed tomography. Many osseous changes seen with computed tomography and magnetic resonance imaging were not radiographically evident. Histologically confirmed soft tissue alterations of the deep digital flexor tendon, impar ligament and marrow were identified with magnetic resonance imaging, but not with conventional radiography. Because of their multiplanar capability and tomographic nature, computed tomography and magnetic resonance imaging surpass conventional radiography for navicular imaging, facilitating earlier, more accurate diagnosis. Current advances in imaging technology should make these imaging modalities available to equine practitioners in the future.

Transient increases in diameter and [Ca(2+)](i) are not obligatory for myogenic constriction

Studies were performed to determine the significance of temporal variation in vascular smooth muscle Ca(2+) signaling during acute arteriolar myogenic constriction and, in particular, the importance of the stretch-induced intracellular Ca(2+) concentration ([Ca(2+)](i)) transient in attaining a steady-state mechanical response. Rat cremaster arterioles (diameter approximately 100 microm) were dissected from surrounding tissues, and vessel segments were pressurized in the absence of intraluminal flow. For [Ca(2+)](i) measurements, vessels were loaded with fura 2 and fluorescence emitted by excitation at 340 and 380 nm was measured using video-based image analysis. Ca(2+) and diameter responses were examined after increases in intravascular pressure were applied as an acute step increase or a ramp function. Additional studies examined the effect of longitudinal vessel stretch on [Ca(2+)](i) and arteriolar diameter. Step increase in intraluminal pressure (from 50 to 120 mmHg) caused biphasic change in [Ca(2+)](i) and diameter. [Ca(2+)](i) transiently increased to 114.0 +/- 2.0% of basal levels and subsequently declined to 106.7 +/- 4.4% at steady state. Diameter initially distended to 125.4 +/- 2.1% of basal levels before constricting to 71.1 +/- 1.2%. In contrast, when the same pressure increase was applied as a ramp function (over 5 min) transient vessel distension and transient increase in [Ca(2+)](i) were prevented, yet at steady state vessels constricted to 71.3 +/- 2.5%. Longitudinal stretch resulted in a large [Ca(2+)](i) transient (158 +/- 19% of basal) that returned to baseline despite maintenance of the stretch stimulus. The data demonstrate that the initial vessel distension (reflecting myocyte stretch) and associated global [Ca(2+)](i) transient are not obligatory for myogenic contraction. Thus, although arteriolar smooth muscle cells are responsive to acute stretch, the resulting changes in myogenic tone may be more closely related to other mechanical variables such as wall tension.

Tyrosine phosphorylation modulates arteriolar tone but is not fundamental to myogenic response

The present study investigated the role of protein tyrosine phosphorylation in myogenic responsiveness of rat skeletal muscle arterioles. Arteriolar segments were cannulated and pressurized without intraluminal flow. All vessels studied developed spontaneous tone and demonstrated significant myogenic constriction to step changes in pressure with a resultant increase in myogenic tone over an intraluminal pressure range of 50-150 mmHg. Step increases in intraluminal pressure from 50 to 120 mmHg caused a rapid and sustained elevation in intracellular [Ca(2+)], as measured using fura 2. Vessels with myogenic tone dilated in response to tyrosine kinase inhibitors genistein (10 or 30 microM) and tyrphostin A47 (10 or 30 microM) and constricted to the tyrosine phosphatase inhibitor pervanadate (1 or 10 microM). Despite the dilator effect, myogenic reactivity was not blocked by the inhibitors. Daidzein (10 microM), a compound structurally similar to genistein but without tyrosine kinase-inhibiting activity, did not alter vessel tone or myogenic responses. Preincubation of arterioles with genistein or tyrphostin A47 did not significantly alter baseline arteriolar [Ca(2+)], and neither drug reduced the increase in [Ca(2+)] following an acute increase in intraluminal pressure. Constriction induced by pervanadate (10 microM) was not accompanied by a significant increase in intracellular [Ca(2+)], even though removal of extracellular Ca(2+) reversed the constriction. Examination of smooth muscle tyrosine phosphorylation, using a fluorescent phosphotyrosine antibody and confocal microscopy, showed that increased intraluminal pressure resulted in an increase in anti-phosphotyrosine fluorescence. Because manipulation of tyrosine kinase activity was found to alter vessel diameter, these data support a role for tyrosine phosphorylation in modulation of arteriolar tone. However, the results indicate that acute arteriolar myogenic constriction does not require tyrosine phosphorylation.

Impaired arteriolar mechanotransduction in experimental diabetes mellitus

Decreased arteriolar distensibility in diabetes may impair signal transduction mechanisms that are required for converting a pressure stimulus into smooth muscle contraction. These studies aimed to determine if pressure-induced increases in arteriolar intracellular Ca(2+) are altered in diabetes and whether diabetes is associated with alterations in composition of the extracellular matrix. Studies of mechanical properties used single, isolated, and cannulated cremaster arterioles from streptozotocin (60 mg/kg) diabetic rats and age-matched controls. To measure Ca(2+)(i), arterioles were loaded with Fura 2 (5 microM) after which preparations were examined by fluorescence microscopy and image analysis. Matrix protein (type IV collagen, laminin, fibronectin) deposition was studied by immunohistochemistry. Over a range of 30-120 mm Hg control vessels showed a linear relationship (r = 0.98, p < 0.01) between intraluminal pressure and Ca(2+)(i). Vessels from diabetic animals also showed a linear relationship (r = 0.99, p < 0.01), however, the mean slope was significantly (p < 0.02) less in the diabetic (0.17 +/- 0.05, n = 5) compared to controls (0.51 +/- 0.09, n = 7). Similarly, the slope of the wall tension-Ca(2+)(i) relationship was significantly decreased in vessels from diabetic animals. These differences were ameliorated by treatment of diabetic animals (n = 5) with aminoguanidine. Increased content of type IV collagen, laminin and fibronectin in vessel media was evident after 2 weeks of diabetes and showed a further increase with duration of diabetes. The data suggest that for a given increase in luminal pressure arterioles from diabetic animals response with an attenuated rise in smooth muscle Ca(2+)(i). This mechanotransduction defect may relate to alterations in the composition of the extracellular matrix within the arteriolar wall.

Alteration of microtubule polymerization modulates arteriolar vasomotor tone

Microtubules are important cytoskeletal elements that have been shown to play a major role in many cellular processes because of their mechanical properties and/or their participation in various cell signaling pathways. We tested the hypothesis that depolymerization of microtubules would alter vascular smooth muscle (VSM) tone and hence contractile function. In our studies, isolated cremaster arterioles exhibited significant vasoconstriction that developed over a 20- to 40-min period when they were treated with microtubule depolymerizing drugs colchicine (10 microM), nocodazole (10 microM), or demecolcine (10 microM). Immunofluorescent labeling of microtubules in cultured rat VSM revealed that both colchicine and nocodazole caused microtubule depolymerization over a similar time course. The vasoconstriction was maintained over a wide range of intraluminal pressures (30-170 cmH(2)O). The increased tone was not affected by endothelial denudation, suggesting that it was due to an effect on VSM. Microtubule depolymerization with demecolcine or colchicine had no effect on VSM intracellular Ca(2+) concentration ([Ca(2+)](i)). These data indicate that microtubules significantly interact with processes leading to the expression of vasomotor tone. The mechanism responsible for the effect of microtubules on vasomotor tone appears to be independent of both the endothelium and an increase in VSM [Ca(2+)](i).

Myogenic reactivity of rat epineurial arterioles: potential role in local vasoregulatory events

Local control of neural blood flow is considered to reside in innervation of epineurial and endoneurial arterioles rather than in intrinsic autoregulatory mechanisms. With the use of an isolated vessel preparation and an in vivo approach, the present studies examined intrinsic vasomotor responsiveness of epineurial arterioles. Segments of epineurial arterioles, cannulated on glass micropipettes (40 micrometers) and pressurized in the absence of intraluminal flow, showed sustained pressure-dependent (30-90 mmHg) vasoconstriction and acute myogenic reactivity. Myogenic tone was unaffected by phentolamine (10(-6) M). Removal of extracellular Ca(2+) resulted in loss of spontaneous tone and passive behavior. Concentration-response curves for norepinephrine (10(-9)-3 x 10(-6) M) and relaxation to both acetylcholine (10(-8)-10(-5) M) and adenosine (10(-8)-10(-4) M) were obtained. Acetylcholine dilator responses were inhibited by N(G)-nitro-L-arginine methyl ester. Epineurial blood flow was measured in vivo using a laser-Doppler flow probe. Blood flow declined over a 2-h period after surgery, and during this time preparations developed responsiveness to the dilator acetylcholine. Phentolamine blocked vasoconstrictor responses to exogenous norepinephrine but only partially reversed the in vivo baseline tone. The time-dependent decline in epineurial blood flow was observed despite the presence of tetrodotoxin (1 microM), further confirming that tone was predominantly caused by myogenic rather than neurogenic mechanisms. It is concluded that because epineurial arterioles exhibit intrinsic myogenic reactivity, they have the potential to participate in local regulation of neural hemodynamics independently of their own innervation.

Elevated expression of FGF-2 does not cause prostate cancer progression in LNCaP cells

BACKGROUND

Androgen-independent (AI) prostate cancer (CaP) resulting from progression of disease is untreatable. Such progression may relate to upregulation and autocrinicity of growth factor expression. We studied one candidate growth factor, basic fibroblast growth factor (FGF-2).

METHODS

LNCaP cells made autocrine for FGF-2 by stable transfection with FGF-2 were examined for cancer progression, measured by 1) altered response to androgen, 2) ability to grow more quickly when cocultured with bone cells in vitro or to form tumors when coinoculated with bone cells in vivo, or 3) increase in metastatic ability.

RESULTS

Stably transfected lines differed in FGF-2 protein expression. LNCaP-HF (high production of FGF-2) expressed more FGF-2 than LNCaP-LF (low production of FGF-2); controls were negative. In vitro, compared with LNCaPs, LNCaP-HF cells showed a slightly increased growth rate, reduced proliferation in response to androgen but not to estrogen or progesterone, and a decreased proliferative response to epidermal growth factor (EGF) and FGF-2. Although giving a slightly faster take rate, LNCaP-HF cells without Matrigel only formed small, fast-regressing tumors in male nude mice, and with Matrigel, did not differ from LNCaPs in growth rate or tumor size. No metastases occurred. No tumors grew in females. Mixed growth of FGF-2 transfectants with human fetal osteoblasts failed to cross-stimulate in vitro, or to allow tumor formation in vivo.

CONCLUSIONS

Although FGF-2 is overexpressed in AI CaPs, our experiments show that upregulation of FGF-2 expression is not sufficient to cause androgen independence, tumorigenicity, or metastases production (i.e., prostate cancer progression) in LNCaP cells.

Lethal effect of carbon K-shell photoionizations in Chinese hamster V79 cell nuclei: experimental method and theoretical analysis

To test a possible specific effect of carbon K-shell ionizations in DNA, survival curves for Chinese hamster V79 cells were measured for X irradiations at energies below and above the carbon K-shell ionization threshold. Specific values of the X-ray energies (250 and 340 eV) were chosen to ensure isoattenuation of the two kinds of radiation within the cell. An enhancement of lethality by a factor of about 2 was found for X rays at 340 eV compared to below the threshold at 250 eV. This may be attributed to the production of highly efficient carbon K-shell ionizations located on DNA. A model of X-ray lethality (Goodhead et al., Radiat. Prot. Dosim. 52, 217-223, 1994) was extended to allow for a possible lethal effect from clusters of reactive species induced by K-shell photoionizations (K-shell clusters). Within this model, the increase in lethality above the carbon K-shell threshold may be explained by a value of 2% for the lethal efficiency of K-shell clusters overlapping the DNA. An extrapolation to the lethal effect of more complex ion-induced K-shell ionizations indicates that K-shell ionization may be a major process in the biological effectiveness of heavy ions.

Radiation damage to DNA: the importance of track structure

A wide variety of biological effects are induced by ionizing radiation, from cell death to mutations and carcinogenesis. The biological effectiveness is found to vary not only with the absorbed dose but also with the type of radiation and its energy, i.e., with the nature of radiation tracks. An overview is presented of some of the biological experiments using different qualities of radiation, which when compared with Monte Carlo track structure studies, have highlighted the importance of the localized spatial properties of stochastic energy deposition on the nanometer scale at or near DNA. The track structure leads to clustering of damage which may include DNA breaks, base damage etc., the complexity of the cluster and therefore its biological repairability varying with radiation type. The ability of individual tracks to produce clustered damage, and the subsequent biological response are important in the assessment of the risk associated with low-level human exposure. Recent experiments have also shown that biological response to radiation is not always restricted to the 'hit' cell but can sometimes be induced in 'un-hit' cells near by.

Reduction of the gamma-ray component from 252Cf fission neutron source--optimization for biological irradiations and comparison with MCNP code

Gamma-rays contribute 33% of the absorbed dose from an unfiltered 252Cf fission neutron source. To reduce this gamma-ray component and to enable radiobiological experiments at as high a dose rate as possible, Monte Carlo calculations for several filter materials (Al, Fe, Pb and concrete) have been made using MCNP neutron and photon transport code version 4a. A lead filter of thickness 4 cm was found to reduce the gamma-ray component to 6.7% of the total dose whilst reducing the neutron dose by only about 10%. Such a filter was installed at the MRC 252Cf neutron irradiation facility and dosimetric measurements were made using a TE-TE chamber and a 7LiF(Mg, Cu, P) TLD. Monte Carlo simulations agree with experimental measurements of neutron and gamma-ray doses within 6%. V79-4 Chinese hamster cells were irradiated with lead-filtered and unfiltered neutrons and also with 60Co gamma-rays at two dose rates. The survival fraction obtained for each radiation was consistent with the reduced gamma-ray dose. The relative biological effectiveness for neutrons alone, corrected for gamma-ray effects, was found to be 9.2 +/- 3.4 from the initial slopes and 3.1 +/- 0.5 at 10% survival, both relative to the acute gamma-rays.

Signaling mechanisms underlying the vascular myogenic response

The vascular myogenic response refers to the acute reaction of a blood vessel to a change in transmural pressure. This response is critically important for the development of resting vascular tone, upon which other control mechanisms exert vasodilator and vasoconstrictor influences. The purpose of this review is to summarize and synthesize information regarding the cellular mechanism(s) underlying the myogenic response in blood vessels, with particular emphasis on arterioles. When necessary, experiments performed on larger blood vessels, visceral smooth muscle, and even striated muscle are cited. Mechanical aspects of myogenic behavior are discussed first, followed by electromechanical coupling mechanisms. Next, mechanotransduction by membrane-bound enzymes and involvement of second messengers, including calcium, are discussed. After this, the roles of the extracellular matrix, integrins, and the smooth muscle cytoskeleton are reviewed, with emphasis on short-term signaling mechanisms. Finally, suggestions are offered for possible future studies.

A technique for magnetic resonance imaging of equine cadaver specimens

We tested an adaptation of a technique for performing magnetic resonance (MR) imaging of human cadaver limbs in the horse. The forelimbs from a normal horse were collected, frozen, and sealed with a paraffin-polymer combination prior to imaging with either a high- or midfield magnetic resonance scanner. Each forelimb was defrosted, scanned, and refrozen on two separate occasions. A five-point scale was used to evaluate the quality of each set of sagittal and transverse, T1-weighted images of each digit. There was no difference in image quality between first and second scans of either specimen (p > 0.05). We conclude that this technique allows investigators to bank tissue specimens for future magnetic resonance imaging without significant loss of image quality.

Effectiveness of 0.28 keV carbon K ultrasoft X-rays at producing simple and complex chromosome exchanges in human fibroblasts in vitro detected using FISH

PURPOSE

To study the effects of carbon K ultrasoft X-rays, which produce a single photoelectron with a track length of < 7 nm, on the production of structural chromosome-type changes.

MATERIALS AND METHODS

Untransformed human fibroblasts (HF12) were irradiated in G1 phase. Aberrations were analysed using fluorescence in situ hybridization using multi-coloured chromosome specific DNA probes for chromosomes 1 and 2 and an alpha-satellite pan-centromeric probe.

RESULTS

CK X-rays have a high efficiency per unit absorbed dose for producing simple and complex exchanges. Mean absorbed doses of 0.33-1.31 Gy produce simple exchanges with a predominantly linear dose dependency, and visibly complex exchanges increased by more than the power 2 of the dose, with no evidence of a linear component. The proportion of exchanges that are visibly complex ranged from 9% to 46%.

CONCLUSIONS

The linear response for simple exchanges provides further support to the hypothesis that damaged DNA may be able to interact with undamaged DNA. The high proportion of complex exchanges may be due to the increased efficiency of double-strand break induction and to the high density of tracks per unit absorbed dose targeting pre-existing sites, some of which may be close to the incident nuclear membrane.

Normal blood flow response and vasomotion in the diabetic Charcot foot

Vasomotion, the spontaneous rhythmic contraction exhibited by small arteries and arterioles is dysregulated in patients with diabetic neuropathy. We examined the relationship between Charcot arthropathy and vasomotion at the dorsum of the foot. We studied nine diabetic patients with clinically diagnosed neuropathy and Charcot arthropathy in 13 feet (n=13), twelve subjects with diabetic neuropathy and no Charcot deformity (n=12), and 11 healthy controls (n=11). Following neuropathy assessment, blood flow was measured by laser Doppler flowmetry with local skin warming. Fast Fourier transformation was performed to provide an index of vasomotion. Subjects with Charcot osteoarthropathy had more severe somatic neuropathy and higher circulating levels of serum calcium (9.8+/-0.1 versus 9.3+/-0.1 mg/dL). Raising local temperature increased skin blood flow and vasomotion in both control subjects and Charcot subjects, but not in diabetic patients with neuropathy alone (p < 0.05 for blood flow, p < 0.02 for vasomotion). Patterns of peripheral vasomotion and blood flow which are clearly disordered in diabetic neuropathy are intact in patients with a Charcot osteoarthropathy, despite a more severe sensory nerve impairment. These findings suggest that the loss of peripheral blood flow and vasomotion often seen in diabetic neuropathy may actually be protective against Charcot arthropathy by preventing bone resorption. It remains unclear then whether the Charcot arthropathy is a direct result of a failure to decrease blood flow to bone, or is the manifestation of some other pathology.

Functional analysis of conserved histidines in ADP-glucose pyrophosphorylase from Escherichia coli

Two absolutely conserved histidines and a third highly conserved histidine are noted in 11 bacterial and plant ADP-glucose pyrophosphorylases. These histidines were individually mutagenized in the E. coli enzyme to glutamine in order to determine their function. Glutamine mutations at residues 143 and 156 produced functional enzymes in cell extracts with slightly lower than wild-type specific catalytic activities and with same heat stability characteristics of the wild-type enzyme. Substitution of residue 83 with glutamine however produced an enzyme having decreased thermal stability. Additional mutageneses at residue 83 with asparagine, arginine, or aspartate gave rise to enzymes having a progressively decreasing trend in thermal stability. These mutants are more susceptible to proteolysis than wild-type enzyme. Kinetic analysis of H83Q and H83N indicates that histidine 83 is not involved in the catalytic mechanism or in substrate binding but possibly in maintenance of the active catalytic structure.

Interleukin-1 and interleukin-6 mediated skeletal muscle arteriolar vasodilation: in vitro versus in vivo studies

Interleukin (IL) 1 and IL-6 have been implicated in the decreased systemic vascular resistance of septic shock; however, their sites of action and underlying mechanisms remain unclear. This study determined the effects of IL-1 and IL-6 on rat skeletal muscle arterioles using both in vitro and in vivo preparations. In the in vitro preparation, first order cremasteric arterioles were isolated from rats, cannulated with micropipettes, pressurized to 70 mmHg, superfused with physiologic saline solution, and allowed to achieve spontaneous basal tone in the absence of intraluminal flow. In the in vivo preparation, the cremaster muscle of anesthetized rats was surgically opened, secured as a flat sheet over an optical pedestal, and superfused with physiologic saline solution. Responses of third order arterioles were studied using transillumination video microscopy. In both arteriolar preparations, vessel diameter and phenylephrine (PE) responsiveness were assessed before and after cytokine exposure and washout. In vitro exposure of IL-1 (20 ng/mL (n=8) or 60 ng/mL (n=4)) or IL-6 (500 U/mL (n=2) or 1,000 U/mL (n=4)) for 1 h did not cause arteriolar vasodilation or change in PE responsiveness. However, during a 1 h in vivo exposure of IL-1 (.01, .1, 1.0, or 20 ng/mL), arteriolar diameter increased from 47+/-2 to 58+/-2% of maximum diameter (Dmax) (n=14, p < .0001), from 45+/-2 to 69+/-3% of Dmax (n=14, p < .0001), from 45+/-3 to 96+/-2% of Dmax (n=8, p < .0001), and from 47+/-4 to 96+/-1% of Dmax (n=14, p < .0001), respectively. Cytokine washout resulted in arteriolar return to basal diameter. Cytokine exposure and washout did not affect arteriolar PE responsiveness. In vivo exposure of IL-6 (10, 50, or 250 U/mL) for 1 h increased diameter from 47+/-2 to 57+/-2% of Dmax (n=14, p < .0001), from 46+/-2 to 75+/-3% of Dmax (n=14, p < .0001), and from 46+/-2 to 68+/-4% of Dmax (n=15, p < .0001), respectively. After washout of IL-6 (10, 50, or 250 U/mL), arteriolar dilation persisted, from 16.3+/-.5 to 20.1+/-1.4 microm (n=14, p < .003), from 16.1+/-.4 to 20.1+/-.6 microm (n=14, p < .0001), and from 17.7+/-.4 to 22.5+/-.8 microm (n=15, p < .0001), respectively. There was no change in PE responsiveness. These data indicate that the cytokines IL-1 and IL-6 are potent dilating agents for skeletal muscle resistance vessels under in vivo conditions. However, given that IL-1 and IL-6 are ineffective in causing relaxation of similar arterioles under isolated in vitro conditions, it is suggested that IL-1 and IL-6 interact with parenchymal or intravascular factors to elicit arteriolar relaxation.

Production and dosimetry of copper L ultrasoft x-rays for biological and biochemical investigations

Ultrasoft x-rays provide a unique tool for investigating the intracellular mechanisms of radiation action. Secondary electrons are produced with a well defined energy and a range comparable with that of critical structures in the cell. Copper L characteristic x-rays of weighted average energy of 956 eV interact within the cell, mainly with the oxygen atom, typically producing a photoelectron with energy 424 eV (95%) followed by an Auger electron with an average energy of 505 eV, with a combined continuous slowing down approximation (csda) range of approximately 40 nm. The attenuation through the cell is similar to that of carbon K x-rays (277 eV, single electron), therefore a useful comparison can be made due to similar dose-averaging factors but different electron configurations (total range, and pairs versus singlets). The production, absorption, dosimetry and biological implications of Cu L x-rays using the Medical Research Council cold cathode source is described extending the number of energies available for study in the ultrasoft region. Design parameters were optimized to overcome the inherently low L-characteristic-to-bremsstrahlung yield ratio. Surface absorbed dose rates of 1 Gy min-1 have been obtained with a bremsstrahlung contamination of less than 0.5%. A confocal microscope was used to make thickness measurements on live cells to allow careful determination of the mean absorbed dose. Survival curves for V79-4 Chinese hamster cells were obtained, showing that Cu L x-rays are substantially more lethal per unit dose than are hard x-rays or gamma-rays, with a relative biological effectiveness (RBE) of 1.8. The data are consistent with the hypothesis that clustered damage at the DNA/chromatin level produced by low-energy electrons is biologically more effective.

Leiomyosarcoma: a 45-year review at Charity Hospital, New Orleans

Approximately 2 to 9% of all soft tissue sarcomas are leiomyosarcomas (LMS). LMS arises nearly exclusively as tumors in adults, with peak incidence occurring in the fifth and sixth decades. The purpose of this study was to analyze disease-specific survival and define prognostic factors in patients with this disease who were treated and followed at a single institution. Fifty-eight cases of LMS were identified in the Tumor Registry of the Medical Center of Louisiana at New Orleans (charity Hospital) from 1950 to 1995. Charts were reviewed and tissue blocks reexamined to confirm the diagnosis. Follow-up information was available for 56 of 58 (96%) patients. Univariate and multivariate analyses were performed to analyze which factors predict outcome. The median survival time was 138 months. Univariate analysis identified age (> 48 years), location (retroperitoneal vs other sites), and extent of disease as prognostic factors. Multivariate analysis revealed that only age and the extent of disease at presentation are independent prognostic indicators. Race, sex, and adjuvant therapy were not significant prognostic factors. Surgical resection remains the therapeutic mainstay for patients with LMS. The value of other treatment modalities is largely limited to surgical failures. The data show that the age of the patient and the extent of disease at presentation are the best predictors of long-term survival. LMS has a good prognosis when complete resection of localized lesions can be achieved.

Detection of K-ras mutations in resected primary leiomyosarcoma

Mutation of the K-ras oncogene occurs frequently in human malignancy. However, there are few reports concerning K-ras mutations in soft-tissue sarcoma, including leiomyosarcoma. We therefore designed a study to determine the prevalence of mutations in the first exon of K-ras in leiomyosarcoma and to evaluate its prognostic potential. Fifty-one leiomyosarcomas were reviewed, and their diagnoses were confirmed on pathological review. Tissue blocks were retrieved, and new sections were prepared for confirmation of diagnosis. Additional tissue sections were used for DNA isolation. PCR and denaturing gradient gel electrophoresis (DGGE) were used to detect K-ras mutations in the first exon of genomic DNA isolated from the specimens. Seven (14%) K-ras mutations were detected using DGGE. Subsequent sequencing of the K-ras gene from each of the mutated tumors confirmed the DGGE results in each case. The median survival for patients whose tumors did not contain mutations of K-ras was 42 months (n = 42) versus 25 months (n = 7) for those with mutations (P = 0.06). However, patients with stages I and II tumors had a median survival of 82 months (n = 28) compared to 28 months for those with stages III and IV disease (n = 20, P = 0.02). The results suggest that K-ras codon 12 mutations are uncommon in leiomyosarcoma; however, when such mutations are found, there is a trend toward worse survival. Furthermore, the data confirm that stage is a significant prognostic indicator.

Impairment of peripheral blood flow responses in diabetes resembles an enhanced aging effect

OBJECTIVE

To test the hypothesis that skin blood flow responses in the fingertip of diabetic patients are impaired and to examine the role of aging in both healthy control subjects and diabetic patients.

RESEARCH DESIGN AND METHODS

We measured cutaneous blood flow using laser Doppler techniques in 40 people with diabetes and in 20 age- and sex-matched healthy control subjects. To induce vasoconstriction, subjects were asked to perform three 1-min stressor tasks: mental arithmetic, contralateral hand grip, and immersion of the contralateral hand in ice water. To induce vasodilatation, a local heat stimulus of 45 degrees C was applied for 5 min.

RESULTS

Basal blood flow did not differ between groups, but vasoconstrictive responses induced by arithmetic or immersion of the contralateral hand in ice-cold water and vasodilatation induced by local heating were severely impaired in diabetic subjects, compared with healthy control subjects (P < 0.01). These responses correlated with autonomic nerve function and deteriorated significantly with advancing age in control subjects, but not in diabetic subjects. Blood flow in younger diabetic subjects resembled that of older control subjects.

CONCLUSIONS

These data demonstrate that diabetes has effects on precapillaries that may by direct or mediated via autonomic nerves, which result in a deficit that resembles premature aging.

Induction and rejoining of DNA double-strand breaks in Chinese hamster V79-4 cells irradiated with characteristic aluminum K and copper L ultrasoft X rays

Characteristic aluminum K (AlK) (energy of 1.5 keV) and copper L (CuL) (energy of approximately 0.96 keV) ultrasoft X rays have been used to investigate the effectiveness of the numerous low-energy secondary electrons produced by low-linear energy transfer (LET) ionizing radiation. Cellular inactivation and induction and rejoining of DNA double-strand breaks (DSBs) in Chinese hamster V79-4 cells irradiated as monolayers with these ultrasoft X radiations have been studied under aerobic and anaerobic conditions. The mean cell thickness, determined by confocal laser scanning fluorescence microscopy, was used to calculate the mean dose to the nucleus of the irradiated cells. Relative to 60Co gamma rays, the relative biological effectiveness (RBE) for cellular inactivation at 10% survival is 1.7 +/- 0.1 and 2.3 +/- 0.3 for AIK and CuL ultrasoft X rays, respectively. The RBE values for induction of DSBs of 2.5 +/- 0.2 and 3.0 +/- 0.3 for AlK and CuL X rays, respectively, were determined after irradiation at 277 K using the technique of pulsed-field gel electrophoresis. Induction of DSBs is linearly dependent on dose. Oxygen enhancement ratios of 1.9 and 2.1 for cellular inactivation and DSB induction, respectively, were obtained with AIK X rays. These values are less than those for 60Co gamma radiation. The repair kinetics for rejoining of DSBs after a dose of 15 Gy is similar for both X-ray energies and 60Co gamma rays with a first half-life of 18-22 +/- 5 min. From these studies, it is suggested that induction of DSBs by low-LET radiations such as 60Co gamma rays reflects clustered damage produced predominantly by low-energy electron "track ends," which represent about 30% of the total dose.

Immunohistochemistry of articular cartilage from immature beagle dogs dosed with difloxacin

Effects of the fluoroquinolone difloxacin on articular-epiphyseal cartilage in growing beagle dogs have been described by light microscopic, electron microscopic, and biochemical methods. Here we present data from an immunohistochemistry study with humeral head cartilage from 3-mo-old beagle dogs after treatment with 1 or 2 oral doses of 300 mg difloxacin/kg body weight. Dogs were euthanatized either 24 hr (single dose) or 48 hr (2 doses) after onset of dosing, and cartilage tissue was stored at -90 degrees C until it was studied by immunohistochemistry. Antibodies against matrix components (collagen II, fibronectin) as well as antibodies against cellular structures (integrins) were used. After single-dose treatment (24-hr group), cartilage lesions such as clefts were not observed, but increased staining for fibronectin was found in cartilage samples from 5 of 6 animals. Markedly increased staining for fibronectin was also demonstrated in the vicinity of clefts within cartilage of all animals of the 48-hr group. Collagen II staining was homogeneously distributed in cartilage from controls and was slightly reduced in territorial matrix in 2 of 6 dogs of the 48-hr group. Integrin staining on chondrocytes was not significantly affected by difloxacin under the given conditions with the exception of a slight reduction of the alpha v integrin chain in 1 of 5 dogs of the 48-hr group. Overall, the most important results is the finding that fibronectin was a sensitive immunohistochemical marker for change in cartilage samples due to difloxacin treatment in dogs.

Tumor specific Epstein-Barr virus infection is not associated with leiomyosarcoma in human immunodeficiency virus negative individuals

BACKGROUND

Recent studies have suggested that the Epstein-Barr virus (EBV) is associated with leiomyosarcoma in children with human immunodeficiency virus (HIV) and in organ transplant recipients. To determine whether EBV is associated with leiomyosarcoma in HIV negative patients, the authors examined resected leiomyosarcomas for EBV and HIV.

METHODS

Twenty-four leiomyosarcomas were studied and their diagnosis confirmed on pathologic review. From these specimens DNA was isolated. Tumor samples were analyzed for EBV and HIV using a polymerase chain reaction (PCR) technique followed by gel electrophoresis and Southern blot analysis. DNA from an EBV-infected human Burkitt's lymphoma cell line and peripheral blood from an HIV positive patient were used as positive controls for the presence of EBV and HIV, respectively. Immunohistochemistry was performed using an antibody to Epstein-Barr nuclear antigen.

RESULTS

HIV was not present in any of the patients analyzed. EBV DNA was detected in tumor tissue; however, 80 cycles of PCR were used before EBV sequences were detected. Therefore, the data indicate that tumor tissue was not infected with EBV. The positive results observed after 80 cycles of PCR were likely due to infiltrating lymphocytes. Immunohistochemistry confirmed the lack of active or latent EBV infection in tumor cells.

CONCLUSIONS

The results indicate that EBV is not associated with sporadic leiomyosarcoma in HIV negative patients. Therefore, the biology of leiomyosarcoma associated with HIV may be substantially different from the more common sporadic form.

ECT for the treatment of intractable mania in two prepubertal male children

We provide case reports of the successful use of electroconvulsive therapy (ECT) for intractable mania in two prepubertal male children. Both children responded well to ECT without significant complications. The report focuses in particular on the procedure and technique of doing ECT in this patient population.

Successful resection of multifocal hepatic adenoma during pregnancy

Hepatic adenoma is an unusual complication of pregnancy. Most of these lesions are solitary and associated with hormonal contraceptives. We believe ours is the first case of successful resection of multifocal hepatic adenoma during pregnancy in a patient with no history of oral contraceptive use.

Elevated pressure stimulates protooncogene expression in isolated mesenteric arteries

The aim of this study was to determine whether an increase in pressure alone is a sufficient stimulus in isolated small arteries to induce the immediate early genes that are associated with vascular wall growth. Mesenteric arteries (303-506 microm diam) were isolated from Wistar rats and subjected to static pressure of 90 mmHg (control) or 140 mmHg (hypertensive). The arteries possessed little active tone or myogenic response to pressure elevation; therefore, both sets of vessels were stretched by similar amounts, but wall stress in the hypertensive vessels was 60-80% above that of controls. After 30, 60, 180, and 360 min, the arteries were fixed in Formalin, embedded in paraffin, and sectioned for in situ hybridization. The levels of mRNA for c-fos increased in the hypertensive arteries 2.33-fold at 30 min and 6.64-fold at 60 min. mRNA for c-myc increased 5.13-fold at 60 min and 5.25-fold at 180 min. After this early response gene induction, 18S rRNA increased in hypertensive vessels: 3.35-fold at 180 min and 4.2-fold at 360 min. These changes were not the result of a nonspecific activation of total gene expression in hypertensive vessels, inasmuch as levels of mRNA for beta-actin did not differ from controls; however, hypertensive and control vessels showed increases at 60 min. These results indicate that increased pressure is a sufficient stimulus for protooncogene induction and rRNA production in vascular smooth muscle cells in the arterial wall and suggest that the mechanical signal is wall stress. Therefore, this model represents a unique tool to complement cultured cells for the study of the signaling pathways in the mechanotransduction of a pressure stimulus.

Impaired peripheral vasomotion in diabetes

OBJECTIVE

To test the hypothesis that vasomotion, the rhythmic contraction exhibited by small arteries and arterioles, is impaired in diabetic subjects compared with healthy control subjects.

RESEARCH DESIGN AND METHODS

We mathematically modeled the oscillations in laser Doppler microvascular measurements taken from the pulpar surface of the index finger in 20 healthy control subjects and 20 age-matched diabetic subjects (8 with type I and 12 with type II diabetes). The mean duration of diabetes was 17.1 +/- 2.3 years, and mean HbA1c was 9.1 +/- 0.4%. Blood flow was measured for 5 min as subjects rested quietly in a closed room. Fast Fourier transformation was performed to provide the frequency power spectrum of each recording. Amplitude of vasomotion was correlated with six quantitative measurements of neuropathy.

RESULTS

Diabetic subjects had impaired low-frequency oscillation vasomotion in 75% of age-matched patients (15 of 20 patients), with mean amplitudes of 24.9 +/- 6.4 vs. 129.0 +/- 33.2 (P < 0.0039). Of six somatic and autonomic neuropathy variables, only the warm thermal sensory threshold correlated significantly with the mean amplitude of vasomotion (r = -0.75, P < 0.0009).

CONCLUSIONS

Patterns of peripheral vasomotion are clearly disordered in diabetes. The loss of low-frequency oscillations observed here suggests a peripheral vascular abnormality that extends past the capillary network to arterial vessels. It is uncertain whether the accompanying small unmyelinated nerve C-fiber dysfunction is a cause or consequence of the impaired microvascular function. Measurement of vasomotion may prove useful as a novel test for peripheral neurovascular function.

Infection of pigs by aerosols of Aujeszky's disease virus and their shedding of the virus

On three consecutive days, six pigs were exposed for 15 minutes to aerosols of Aujeszky's disease virus. The total estimated dose was 4.5 log 10 TCID50. Within each isolation room, a sentinel pig was placed on a deck two feet away from the infected pig. The breath of the pigs that had inhaled the aerosols was collected on days 3, 7 and 13. The respiratory and other clinical signs of the infected pigs resembled those in field cases of Aujeszky's disease. All the pigs infected with Aujeszky's disease virus seroconverted within seven to 10 days after infection. Among the sentinel pigs, clinical signs were minimal and only three seroconverted.

Endotoxin interacts with tumor necrosis factor-alpha to induce vasodilation of isolated rat skeletal muscle arterioles

Sepsis is characterized by decreased peripheral vascular resistance, however, discrepancies exist regarding the specific secondary mediators involved. This study examined whether the presence of endotoxin (ET) is a requirement for tumor necrosis factor-alpha (TNF-alpha) to induce vasodilation of isolated skeletal muscle arterioles. First order cremasteric arterioles were isolated from male Sprague-Dawley rats, cannulated with glass micropipettes, superfused in physiologic saline, and allowed to achieve spontaneous basal tone in the absence of intraluminal flow. A 2 min exposure to TNF-alpha (.01-100 ng/mL) had no apparent effect on arteriolar diameter (95 +/- 5% after .01 ng/mL and 92 +/- 6% after 100 ng/mL, p > .05 compared with basal). However, arterioles superfused with 2.5 micrograms/mL Salmonella enteritidis ET for 1 h followed by a 2 min exposure to 100 ng/mL TNF-alpha demonstrated a dilation (to 128 +/- 12%) that became statistically significant 10 min after TNF-alpha washout (to 142 +/- 12%, p < .05). This effect was eliminated by combined inhibition of cycloxygenase (with indomethacin) and nitric oxide synthase (L-NAME). The data indicate that neither ET or TNF-alpha alone elicit a direct vasomotor effect on the isolated arteriole preparation used in these studies. However, pretreatment of the vessels with ET results in the ability of TNF-alpha to cause arteriolar dilation, possibly through a mechanism involving both cyclooxygenase and nitric oxide synthase.

Calcium dependence of indolactam-mediated contractions in resistance vessels

The protein kinase C activator, (-)-indolactam, has been shown to enhance reactivity of arterioles by a mechanism not requiring an increase in intracellular Ca++ (Ca++i). The aim of this study was to characterize the Ca++ requirement for indolactam-induced contraction of resistance vessels. Studies were performed in small mesenteric arteries (diameter, 260 +/- microm), using intact segments or after permeabilization with alpha-toxin (500 U/ml). Additional studies were preformed using isolated smooth muscle cells to allow electrophysiological assessment of the effect of indolactam on voltage-gated Ca++ entry. Intact and permeabilized vessel segments showed dose-dependent constriction to indolactam. Studies of Fura 2-loaded vessels and permeabilized segments maintained at low Ca++i, showed that the constriction occurred without an overt increase in Ca++i. That Ca++ was required was evident by near maximal relaxation after the removal of Ca++. Patch clamp studies indicated that indolactam potentiated voltage-gated Ca++ entry; however, nifedipine (0.5 microM) and La (0.2 or 1 mM) were relatively ineffective in reversing the contraction, indicating that voltage-gated Ca++ entry was not an absolute requirement. In intact vessel segments, the myosin light chain (MLC) kinase inhibitors, ML-7 and ML-9, reversed the indolactam contraction, suggesting the requirement of the MLC chain phosphorylation pathway. Furthermore, indolactam caused by a significant increase in MLC phosphorylation in permeabilized vessels, despite clamping of Ca++i at pCa 7.0. The data are consistent with the suggestion that the protein kinase C activator, indolactam, acts to modulate the Ca++ sensitivity of the smooth muscle contractile process such that higher than expected levels of MLC phosphorylation exist for a given level of Ca++i.

Experimental osteoarthritis in dogs: a comparison of the Pond-Nuki and medial arthrotomy methods

Lesions induced by transecting the cranial cruciate ligament in two surgical models of osteoarthritis (OA) in mature, male, cross-bred dogs were compared by using an established grading system and alternatives. Previously, we relied on evaluations of lesions in articular cartilage on femurs alone. No statistically significant differences were found between grades for lesions in cartilage when either treated or control joints were compared by surgical method. Because the Pond-Nuki method yielded statistically significant differences between grades for lesions affecting treated and control femurs or tibias, and for some parameters indicative of synovitis, we preferred this method of surgery. Although by using the medial arthrotomy method of surgery, we were able to destabilize the joint in a more consistent manner, significant differences between treated and control joints were found for lesions on tibias, but not femurs, a frequent site for OA in humans. Suggestions are made for enhancing the surgical models and for a more holistic approach to evaluating joints morphologically.

The effect of thyroid hormone supplementation on hemodynamic stability and survival in an endotoxin-induced model of physiologic stress

Severe physiologic stress is associated with intense changes in the systemic hormonal milieu. Among these changes are suppression of the thyroid hormone axis resulting in decreased levels of triiodothyronine (T3) and thyroxine (T4). This study was conducted to determine whether supplemental T3 or T4 improved (1) hemodynamic stability and/or (2) survival following a standardized level of endotoxin (ET)-induced physiologic stress. Forty-eight hours after placement of internal jugular vein and carotid artery cannulas, male Sprague-Dawley rats (n = 91) were subjected to ET (15 or 20 mg/kg Salmonella enteritidis ET). Following an ET-induced decrease in mean arterial pressure (MAP), the animals received a continuous infusion of normal saline (NS), T3 (0.08, 0.4, or 2.0 micrograms/kg/hr), 0.4 microgram/kg/hr T3 in conjunction with 25 or 50 micrograms/min phenylephrine (PE), 0.4 microgram/kg/hr T3 and 5 micrograms/min dopamine, or 4.0 micrograms/kg/hr T4. There were no statistically significant differences in MAP during a 24-hr monitoring period among treatment groups. At 24 hr, there were no statistically significant differences in survival among animals treated with T3 alone (P > 0.05). Treatment with 4.0 micrograms/kg/hr T4 produced a 24-hr survival of 78% (versus 52% NS controls); however, this was not significant (P > 0.05). Phenylephrine administered in conjunction with T3 yielded a worse survival when compared to controls (0% versus 44%, P < 0.05); however, treatment with dopamine and T3 resulted in no change in survival at 24 hr (25%, P > 0.05). Within the dose ranges studied, T3 alone or in conjunction with dopamine or T4 alone did not improve hemodynamic stability or survival in an ET-induced model of physiologic stress. T3 in conjunction with PE resulted in a significantly worse survival after ET.

Role of myosin phosphorylation and [Ca2+]i in myogenic reactivity and arteriolar tone

The aim of this study was to define the relationship between intraluminal pressure, intracellular calcium concentration ([Ca2+]i), and myosin light-chain (MLC) phosphorylation in isolated arterioles exhibiting myogenic tone. Cremaster muscles were removed from anesthetized rats, and arterioles (approximately 100-microns diam) were dissected from surrounding tissues and cannulated on glass pipettes. Vessels were warmed to 34 degrees C and initially pressurized to 70 mmHg in the absence of intraluminal flow. For [Ca2+]i measurements, vessels were loaded with 5 microM fura 2, and fluorescence emitted by excitation at 340 and 380 nm was measured. Data were considered in terms of changes in the fluorescence ratio (340/380 nm) and collected at steady-state intraluminal pressures between 30 and 170 mmHg. For measurement of MLC phosphorylation, vessels were frozen in acetone-dry ice followed by sonication in homogenizing buffer. Homogenates were separated by two-dimensional gel electrophoresis, and proteins were visualized by silver staining. MLC phosphorylation was quantitated photodensitometrically, and results are expressed as percent total 20-kDa MLC. Increasing intraluminal pressure resultedin significant constriction with increased [Ca2+]i and MLC phosphorylation. For example, the fluorescence ratio was 0.80 +/- 0.04 at 30 mmHg compared with 1.02 +/- 0.05 at 120 mmHg (n = 7 vessels); corresponding MLC-phosphorylation values were 27.7 +/- 1.6 and 39.6 +/- 3.0% (n = 6). MLC phosphorylation in arterioles superfused with 0 mM Ca(2+)-2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) was 8.5 +/- 0.7%.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of direct endotoxin-induced vasoactive effects on isolated skeletal muscle arterioles

Septic shock continues to be a major cause of mortality in the intensive care unit. This study was conducted to determine if endotoxin exerts a direct effect on the major determinant of peripheral vascular resistance, skeletal muscle arterioles. First order cremasteric arterioles were isolated from male Sprague-Dawley rats, cannulated with glass micropipettes, superfused in physiologic saline solution, and allowed to achieve spontaneous basal tone in the absence of intraluminal flow. Phenylephrine responsiveness was assessed before and after exposure to 2.5 micrograms/mL Salmonella enteritidis endotoxin (ET) for 1-2 h. There was no change in either basal diameter (91 +/- 5 microns before ET and 98 +/- 5 microns after ET) or phenylephrine responsiveness. In vivo exposure to ET (15 mg/kg) resulted in no change in basal tone at 1 h, however increased tone was observed in arterioles harvested after 4 h of systemic ET (43 +/- 4% without ET and 57 +/- 3% with, p < .05). To determine if upstream conduit vessels released factors responsible for the vasodilation of skeletal muscle arterioles, isolated cannulated cremasteric arterioles were connected in series to a 1 cm segment of aorta and superfused without and with 2.5 micrograms/mL ET. An increase in basal diameter was observed in arterioles from 94 +/- 14 microns before ET to 120 +/- 17 microns after ET (p < .05). These studies demonstrate that ET has no direct effect on isolated cannulated skeletal muscle arterioles, and that a vasodilating substance not consistent with nitric oxide is released from the upstream arterial bed.

Active and passive mechanical properties of isolated arterioles from STZ-induced diabetic rats. Effect of aminoguanidine treatment

Studies were performed to examine the effect of experimental diabetes (4-6 weeks duration) on both the passive elastic and active myogenic properties of isolated skeletal muscle arterioles. Studies were conducted on untreated streptozotocin (60 mg/kg)-induced diabetic rats and in similar rats treated daily with either amino-guanidine (25 mg/kg) or methylguanidine (25 mg/kg). First-order cremaster muscle arterioles were isolated, cannulated, and pressurized in the absence of intraluminal flow. Video microscopy was used to determine relationships between arteriolar diameter and intraluminal pressure both in the active and passive (o mmol/l Ca(2+)-2 mmol/l EGTA superfusated) tes. The measurements were used to calculate active myogenic responses, arteriolar distensibility, and stress-strain relationships. Under passive conditions, arterioles from untreated diabetic animals appeared to be stiffer and less distensible compared with similar arterioles from control animals. Under active conditions, i.e., in the presence of extracellular Ca2+, arterioles from the untreated diabetic group showed impaired myogenic reactivity as evidenced by a significant (P < 0.001) reduction in the negative slope of the pressure-diameter relationship over a physiological range of intraluminal pressures. Chronic treatment with aminoguanidine prevented the diabetes-induced changes in the active and passive properties of the isolated arterioles while treatment with methylguanidine appeared ineffective. Vasodilator responses to topically applied acetylcholine (10(-8) to 5 x 10(-6) mol/l) were significantly impaired in diabetic animals irrespective of treatment with aminoguanidine. The data indicate that experimental diabetes is associated with a decreased passive distensibility, or stiffening, of skeletal muscle arterioles that, in addition, may contribute to impaired active myogenic responses.

Regulation of rat liver phenylalanine hydroxylase. II. Substrate binding and the role of activation in the control of enzymatic activity

Activation by phenylalanine and reduction by the co-factor (6R)-tetrahydrobiopterin (BH4) are required for formation of active liver phenylalanine hydroxylase. This work describes effects of the activation and redox state on substrate and effector recognition of this enzyme, it establishes relationships among the pterin and phenylalanine binding sites on the different forms of the enzyme, and it provides a quantitative description of the enzyme's presumptive regulatory and catalytic sites. BH4, 7,8-dihydrobiopterin (BH2), 6-methyltetrahydropterin, and 5-deaza-6-methyltetrahydropterin were found to bind to unactivated phenylalanine hydroxylase with a stoichiometry of 1/enzyme subunit and with hyperbolic kinetics; all appear to compete for the same binding site on the enzyme, and all appear to bind in the proximity of, but not to, the enzyme's non-heme iron. In the transition from unactivated to activated enzyme, phenylalanine and pterin binding is modified, a new site for phenylalanine is formed, and the pterin site is replaced by a site of greatly decreased affinity for BH4 and BH2, one which does not appear to recognize the dihydroxypropyl side chain of BH4 and BH2. The pterin- and phenylalanine-binding sites on activated phenylalanine hydroxylase appear to be part of the enzyme's active site. Despite large effects on substrate binding, neither chelator binding ability nor solvent accessibility of the iron are affected by activation; activation appears to affect the nearby environment of the enzyme's iron but not the iron itself. Studies of oxidized and reduced phenylalanine hydroxylase indicate that the redox state is not a major determinant of pterin and phenylalanine association with enzyme.

Regulation of rat liver phenylalanine hydroxylase. I. Kinetic properties of the enzyme's iron and enzyme reduction site

Tetrahydropterins react with phenylalanine hydroxylase at a redox site, a regulatory site, and the catalytic site, but neither the properties of nor relationships among these sites are well understood. We have studied the redox site using the fluorescent iron chelators 2,3-dihydroxynaphthalene and bathophenanthroline; these compounds act as site-specific reporter groups for reactions on oxidized and reduced enzyme, respectively. The chelators bind reversibly and specifically to the enzyme's iron with 1:1 stoichiometry, high affinity (Kd values approximately 1 nM), and complete quenching of their own fluorescence. The kinetic behavior of these and other iron chelators indicates that the enzyme's iron is solvent accessible and in a hydrophobic pocket of the protein. Both ferrous and ferric chelators inhibit phenylalanine hydroxylase activity. Bathophenanthroline inhibits by binding to Fe2+ on reduced, active enzyme. 2,3-Dihydroxynaphthalene inhibits by binding to Fe3+ on enzyme that is oxidized during catalysis. This oxidation occurs approximately 1/150 enzyme turnovers, and its rate is increased when p-chloro- or p-fluorophenylalanine is used as the reaction substrate. Studies of the reaction of tetrahydrobiopterin (BH4) at the enzyme's redox site showed that BH4 reduces the enzyme more slowly than 6-methyltetrahydropterin under catalytic and non-catalytic conditions. Reduction occurs at a distinct site whose binding determinants and reaction characteristics are different from those of the BH4 regulatory or catalytic sites, and phenylalanine-activated enzyme is reduced more rapidly than unactivated enzyme. In reducing phenylalanine activated enzyme, BH4 donates one electron/subunit (1/iron atom); the reduction kinetics suggest a trihydrobiopterin-free radical as a reaction intermediate.

Serum-induced signal transduction determines the peripheral location of beta-actin mRNA within the cell

Cell motility is dependent upon the reorganization of the cellular cytoskeleton. Actin filaments form the major component of the cytoskeleton and respond rapidly to serum growth factors. We have previously shown that myoblasts sort the two cytoskeletal beta- and gamma-actin isoform mRNAs to different intracellular regions and that only beta-actin mRNA was associated with peripheral regions of cell motility (Hill, M.A. and P. Gunning. 1993. J. Cell Biol. 122: 825-832). We now show by in situ hybridization that 3T3 fibroblasts similarly sort actin isoform mRNAs and that peripheral beta-actin mRNA is regulated by serum. In the absence of serum, we could not detect beta-actin mRNA at the periphery. Addition of serum rapidly redistributed beta-actin mRNA to the periphery. gamma-actin mRNA distribution was not altered by serum addition at any time. Both proteins, as identified by immunochemistry with isoform-specific antibodies, were found in similar cellular structures. Serum-stimulated cell motility is mediated through the GTPase signal transduction pathway. We find that an RNA-binding protein, p62, that is part of this pathway, displays a localization pattern similar to beta-actin mRNA. Our results suggest a new biological mechanism which integrates signal transduction with the supply of an architectural component required for membrane remodeling. We propose that active transport of beta-actin mRNA to regions of cell motility is one possible objective of these signal transduction pathways.

Calcium entry and myogenic phenomena in skeletal muscle arterioles

Studies were conducted to examine Ca2+ entry in several vasomotor situations related to myogenic properties of arterioles (basal tone, vasomotion, and responsiveness to alterations in intravascular pressure). In vivo studies were performed on small cremaster muscle arterioles of anesthetized rats. Intravascular pressure was increased using the pressure-box technique. Voltage-operated Ca2+ channel (VOC) activity was inhibited by nifedipine or methoxyverapamil and was stimulated with BAY K 8644. To examine the effect of hyperpolarization, studies were performed in the presence of pinacidil. Nifedipine and methoxyverapamil exhibited a trend toward dose-dependent dilation; however, neither agent caused dilation comparable to adenosine (10(-4) M). BAY K 8644 produced a biphasic effect, constriction below 10(-8) M, and dilation at higher levels. These data indicate that basal tone can be modulated by agents acting on VOCs; however, as high concentrations of nifedipine do not abolish tone, other mechanisms contribute. At similar concentrations, the Ca2+ channel antagonist significantly inhibited vasomotion, abolishing vasomotion at concentrations above 5 x 10(-6) M. In contrast, BAY K 8644 caused a dose-dependent increase in vasomotion amplitude (e.g., 269 +/- 52% of basal at 10(-7) M). Thus vasomotion appears highly dependent on VOCs. Experiments performed in the presence of the antagonists/agonists indicated that VOCs are not the prime determinant of constrictor responses to acute increases in intravascular pressure. Exposure to pinacidil resulted in dose-dependent vasodilatation and inhibition of vasomotion while showing little effect on acute myogenic responses. Similar effects of pinacidil were observed in isolated, cannulated, cremaster arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)