Spatio-Temporal Nonlinear Modeling of Gastric Myoelectrical Activity

The accomplishment of a complete digestive process of human stomach is regulated by a spatio-temporally-coordinated electric pattern called gastric myoelectrical activity (GMA). The normal patterns of GMA present temporal evolution from endogenous rhythmic oscillation to bursting of spikes associated with contractions, and also ordered spatial propagation of the oscillating waves. The abnormal patterns of GMA have been observed in temporal dysrhythmia, such as tachygastria, bradygastria and arrhythmia, and in spatial propagation failure, such as retrograde propagation and uncoupling. Different GMA patterns are associated with different gastric symptoms and there exist some nonlinear mechanisms to govern the formation and dynamic evolution of these patterns. However, these mechanisms are so complex that few of them are known by medical observations. The aim of this study is to explore these mechanisms by spatio-temporal modeling of GMA. The single-cell model simulating the formation process of slow waves and spikes, the multi-cell model simulating the propagation process of GMA and the extracellular model simulating the formation of bipolar recordings are presented.

The Hong-Ou-Mandel interferometer: a new procedure for alignment

Two major requirements in the construction of the Hong-Ou-Mandel interferometer are the alignment and length balancing of two optical paths. A new method is presented for meeting these requirements that requires no custom optics or expensive equipment. Using this method, a two photon interferometer sourced by degenerate noncollinear parametric photon pairs was aligned and the optical paths were balanced to within an average of 11.6 microm, yielding two-photon interference features with visibilities of approximately 0.9. The method is applicable to arbitrary noncollinear emission angles, including nondegenerate downconversion situations where the signal and idler emission angles differ.

Energy separation of neutrons scattered at small angles from silicon using time-of-flight techniques

The time-of-flight technique is used on a small-angle neutron scattering instrument to separate the energies of the scattered neutrons, in order to determine the origin of the temperature-dependent scattering observed from silicon atQ> ∼0.1 Å−1. A quantitative analysis of the results in comparison with the phonon dispersion curves, determined by Dolling using a triple-axis neutron spectrometer, shows that the temperature-dependent scattering can be understood in terms of Umklapp processes whereby neutrons gain energy from phonons.

Stress induced in heart and other tissues by rat dermal exposure to JP-8 fuel

Limited information is available regarding the development of systemic organ stress by dermal exposure to JP-8 fuel. In this study, the systemic stress potential of this fuel is evaluated in a rat model subjected to dermal applications of JP-8 for 7 days at 300 microl per day. Tissue histology indicated that JP-8 induces morphological alterations that suggest that tissue stress in the heart is more substantial than stress in the kidney and liver. Immunoblot analysis of tissues revealed increased levels of the inducible heat shock protein 70 (HSP70) in the heart, kidney, and liver after this dermal JP-8 exposure. This exposure also leads to increased levels of heme oxygenase-1 (HO-1/HSP3) in the liver. Additionally during this exposure, a negative regulator of inflammation, IkappaBalpha (inhibitor of NF-kappaB), was increased in the liver, slightly increased in the kidney, and not increased in the heart. Two regions of the rat brain were also examined and HSP70 and IkappaBalpha were increased in the cerebellum but not significantly increased in the cortex. This study indicates dermal JP-8 exposure causes systemic alterations that are associated with cytoprotective activities (e.g., in the liver) as well as potentially toxic mechanisms (heart and kidney).

Overexpression of Na+/Ca2+ exchanger alters contractility and SR Ca2+ content in adult rat myocytes

The functional consequences of overexpression of rat heart Na+/Ca2+ exchanger (NCX1) were investigated in adult rat myocytes in primary culture. When maintained under continued electrical field stimulation conditions, cultured adult rat myocytes retained normal contractile function compared with freshly isolated myocytes for at least 48 h. Infection of myocytes by adenovirus expressing green fluorescent protein (GFP) resulted in >95% infection as ascertained by GFP fluorescence, but contraction amplitude at 6-, 24-, and 48-h postinfection was not affected. When they were examined 48 h after infection, myocytes infected by adenovirus expressing both GFP and NCX1 had similar cell sizes but exhibited significantly altered contraction amplitudes and intracellular Ca2+ concentration ([Ca2+]i) transients, and lower resting and diastolic [Ca2+]i when compared with myocytes infected by the adenovirus expressing GFP alone. The effects of NCX1 overexpression on sarcoplasmic reticulum (SR) Ca2+ content depended on extracellular Ca2+ concentration ([Ca2+]o), with a decrease at low [Ca2+]o and an increase at high [Ca2+]o. The half-times for [Ca2+]i transient decline were similar, suggesting little to no changes in SR Ca2+-ATPase activity. Western blots demonstrated a significant (P < or = 0.02) threefold increase in NCX1 but no changes in SR Ca2+-ATPase and calsequestrin abundance in myocytes 48 h after infection by adenovirus expressing both GFP and NCX1 compared with those infected by adenovirus expressing GFP alone. We conclude that overexpression of NCX1 in adult rat myocytes incubated at high [Ca2+]o resulted in enhanced Ca2+ influx via reverse NCX1 function, as evidenced by greater SR Ca2+ content, larger twitch, and [Ca2+]i transient amplitudes. Forward NCX1 function was also increased, as indicated by lower resting and diastolic [Ca2+]i.

Sprint training shortens prolonged action potential duration in postinfarction rat myocyte: mechanisms

Two electrophysiological manifestations of myocardial infarction (MI)-induced myocyte hypertrophy are prolongation of action potential duration (APD) and reduction of transient outward current (I(to)) density. Because high-intensity sprint training (HIST) ameliorated myocyte hypertrophy and improved myocyte Ca(2+) homeostasis and contractility after MI, the present study evaluated whether 6-8 wk of HIST would shorten the prolonged APD and improve the depressed I(to) in post-MI myocytes. There were no differences in resting membrane potential and action potential amplitude (APA) measured in myocytes isolated from sham-sedentary (Sed), MI-Sed, and MI-HIST groups. Times required for repolarization to 50 and 90% APA were significantly (P < 0.001) prolonged in MI-Sed myocytes. HIST reduced times required for repolarization to 50 and 90% APA to values observed in Sham-Sed myocytes. The fast and slow components of I(to) were significantly (P < 0.0001) reduced in MI-Sed myocytes. HIST significantly (P < 0.001) enhanced the fast and slow components of I(to) in MI myocytes, although not to levels observed in Sham-Sed myocytes. There were no significant differences in steady-state I(to) inactivation and activation parameters among Sham-Sed, MI-Sed, and MI-HIST myocytes. Likewise, recovery from time-dependent inactivation was also similar among the three groups. We suggest that normalization of APD after MI by HIST may be mediated by restoration of I(to) toward normal levels.

A minimal cytoplasmic subdomain of the erythropoietin receptor mediates p70 S6 kinase phosphorylation

Erythropoietin (EPO) is a lineage-restricted growth factor that is required for erythroid proliferation and differentiation. EPO stimulates the phosphorylation and activation of p70 S6 kinase (p70 S6K), which is required for cell cycle progression. Here, the minimal cytoplasmic domains of the EPO receptor (EPO-R) required for p70 S6K activation were determined.Ba/F3 cells were stably transfected with wild-type (WT) EPO-R or EPO-R carboxyl-terminal deletion mutants, designated by the number of amino acids deleted from the cytoplasmic tail (-99, -131, -221). Transfected cells were growth factor deprived and then stimulated with EPO. p70 S6K, JAK2, IRS-2, and ERK1/2 phosphorylation/activation were examined. The ability of transfected 3-phosphoinositide-dependent protein kinase 1 (PDK1) to reconstitute p70 S6K phosphorylation in EPO-R mutants also was determined. Phosphorylation and activation of p70 S6K, JAK2, IRS-2, and ERK1/2 in Ba/F3 cells transfected with EPO-R-99 or EPO-R-99Y343F were similar to WT EPO-R. In contrast, EPO-dependent p70 S6K phosphorylation/activation, as well as IRS-2 and ERK1/2 phosphorylation, were minimal or absent in cells transfected with EPO-R-131 or EPO-R-221. JAK2 phosphorylation was reduced significantly in cells transfected with EPO-R-131 and abolished with EPO-R-221. To examine the role of PDK1, a kinase known to phosphorylate p70 S6K, Ba/F3 EPO-R-131 cells were transiently transfected with PDK1. WT constitutively active PDK1 restored p70 S6K phosphorylation in Ba/F3 EPO-R-131 cells but not in Ba/F3 EPO-R-221 cells. The results demonstrate that a minimal cytoplasmic subdomain of the EPO-R extending between -99 and -131 is required for p70 S6K phosphorylation and activation. The results also demonstrate that PDK1 is a critical component in this signaling pathway, which requires the presence of domains between -131 and -221 for its activation of p70 S6K.

Dose distributions at extreme irradiation depths of gamma knife radiosurgery: EGS4 Monte Carlo calculations

The accuracy of the dose planning system (Leksell GammaPlan), used in Gamma Knife (type B) radiosurgery at extreme irradiation depths, was verified using the Monte Carlo technique. EGS4 Monte Carlo calculations were employed to calculate the dose distribution along the x, y and z axes for an irradiation relatively shallow in a spherical bony cavity water phantom. Two different sizes of the collimator helmets, 8 and 18 mm, of the Leksell Gamma Knife Unit were studied. The results of GammaPlan showed good consistency with the Monte Carlo results. Furthermore, small dose enhancements were observed in the skull bone where accurate dose measurements are difficult due to the presence of the air-phantom interface. Therefore, the results of this project can promote confidence to all Gamma Knife centres in the world when using the Leksell GammaPlan.

Molecular mechanisms of erythropoietin signaling

Erythropoietin is an obligatory growth factor for red blood cell production. The receptor for erythropoietin contains a single membrane-spanning domain with no intrinsic tyrosine kinase motifs. On binding to erythropoietin, the receptor dimerizes and activates multiple intracellular signaling molecules, including but not limited to JAK2, STAT5, PI 3-kinase, IRS-2, RAS, and Ca2+ channels. This review focuses on cytoplasmic signaling cascades involved in erythropoietin action.

Expression of angiotensin II type I receptor on erythroid progenitors of patients with post transplant erythrocytosis

BACKGROUND

The pathogenesis of posttransplant erythrocytosis (PTE) has been elusive. Angiotensin converting enzyme inhibitors (ACEI) are efficacious in lowering the hematocrit of patients with PTE and angiotensin II (AII) type I receptors (AT1R) were recently detected on red blood cell precursors, burst-forming unit-erythroid- (BFU-E) derived cells. The purpose of this study was to determine whether there is increased expression of the AT1R on BFU-E-derived cells of patients with PTE, which might contribute to the pathogenesis of PTE.

METHODS

Twelve healthy volunteers and 25 transplant recipients (13 patients with and 12 without PTE) were studied. BFU-E from peripheral blood were cultured in methylcellulose and BFU-E-derived colonies were harvested on day 10. Western blotting was used to detect AT1R and erythropoietin receptor (EpoR) expression. Intracellular free calcium in response to AII and erythropoietin (Epo) was measured with digital video imaging.

RESULTS

There were no differences between transplant patients, with and without PTE, with respect to weight, age, sex, blood pressure, serum creatinine, circulating renin, angiotensin II, and Epo levels. Hematocrit, red blood cell number, BFU-E-derived colony number,and size were significantly increased in PTE compared with other two groups. AT1R expression was increased by 44% on the erythroid progenitors of PTE versus non posttransplant erythrocytosis patients and by 32% in PTE patients versus normal volunteers. AT1R expression correlated significantly with the hematocrit in PTE (Spearman r=0.68, P=0.01). In contrast, EpoR expression was equivalent in all groups. The AT1R was functional since a significant increase in [Ca(i)] was observed in Fura-2 loaded day 10 cells when stimulated with AII (182%, P<0.0001).

CONCLUSION

An increase in AT1R density was observed in erythroid precursors of transplant patients with PTE compared to those without PTE and normal volunteers, and the level of AT1R expression in PTE correlated significantly with the hematocrit. In contrast, EpoR expression was not different in PTE compared with non posttransplant erythrocytosis or normal controls. This study supports a role for the AT1 receptor signaling pathway in the pathogenesis of PTE.

Sprint training restores normal contractility in postinfarction rat myocytes

The significance of 6-8 wk of high-intensity sprint training (HIST) on contractile abnormalities of myocytes isolated from rat hearts with prior myocardial infarction (MI) was investigated. Compared with the sedentary (Sed) condition, HIST attenuated myocyte hypertrophy observed post-MI primarily by reducing cell lengths but not cell widths. At high extracellular Ca(2+) concentration (5 mM) and low pacing frequency (0.1 Hz), conditions that preferentially favored Ca(2+) influx over efflux, MI-Sed myocytes shortened less than Sham-Sed myocytes did. HIST significantly improved contraction amplitudes in MI myocytes. Under conditions that favored Ca(2+) efflux, i.e., low extracellular Ca(2+) concentration (0.6 mM) and high pacing frequency (2 Hz), MI-Sed myocytes contracted more than Sham-Sed myocytes. HIST did not appreciably affect contraction amplitudes of MI myocytes under these conditions. Compared with MI-Sed myocytes, HIST myocytes showed significant improvement in time required to reach one-half maximal contraction amplitude shortening, maximal myocyte shortening and relengthening velocities, and half time of relaxation. Our results indicate that HIST instituted shortly after MI improved cellular contraction in surviving myocytes. Because our previous studies demonstrated that, in post-MI myocytes, HIST improved intracellular Ca(2+) dynamics, enhanced sarcoplasmic reticulum Ca(2+) uptake and Ca(2+) content, and restored Na(+)/Ca(2+) exchange current toward normal, we hypothesized that improvement in MI myocyte contractile function by HIST was likely mediated by normalization of cellular Ca(2+) homeostatic mechanisms.

Sprint training normalizes Ca(2+) transients and SR function in postinfarction rat myocytes

Previous studies have shown that myocytes isolated from sedentary (Sed) rat hearts 3 wk after myocardial infarction (MI) undergo hypertrophy, exhibit altered intracellular Ca(2+) concentration ([Ca(2+)](i)) dynamics and abnormal contraction, and impaired sarcoplasmic reticulum (SR) function manifested as prolonged half-time of [Ca(2+)](i) decline. Because exercise training elicits positive adaptations in cardiac contractile function and myocardial Ca(2+) regulation, the present study examined whether 6-8 wk of high-intensity sprint training (HIST) would restore [Ca(2+)](i) dynamics and SR function in MI myocytes toward normal. In MI rats, HIST ameliorated myocyte hypertrophy as indicated by significant (P </= 0.05) decreases in whole cell capacitances [Sham-Sed 179 +/-12 (n = 20); MI-Sed 226 +/- 7 (n = 20); MI-HIST 183 +/- 11 pF (n = 19)]. HIST significantly (P < 0.0001) restored both systolic [Ca(2+)](i) [Sham-Sed 421 +/- 9 (n = 79); MI-Sed 350 +/- 6 (n = 70); MI-HIST 399 +/- 9 nM (n = 70)] and half-time of [Ca(2+)](i) decline (Sham-Sed 0. 197 +/- 0.005; MI-Sed 0.247 +/- 0.006; MI-HIST 0.195 +/- 0.006 s) toward normal. Compared with Sham-Sed myocytes, SR Ca(2+)-ATPase expression significantly (P < 0.001) decreased by 44% in MI-Sed myocytes. Surprisingly, expression of SR Ca(2+)-ATPase was further reduced in MI-HIST myocytes to 26% of that measured in Sham-Sed myocytes. There were no differences in calsequestrin expression among the three groups. Expression of phospholamban was not different between Sham-Sed and MI-Sed myocytes but was significantly (P < 0.01) reduced in MI-HIST myocytes by 25%. Our results indicate that HIST instituted shortly after MI improves [Ca(2+)](i) dynamics in surviving myocytes. Improvement in SR function by HIST is mediated not by increased SR Ca(2+)-ATPase expression, but by modulating phospholamban regulation of SR Ca(2+)-ATPase activity.

Spatio-temporal nonlinear modeling of gastric myoelectrical activity

The accomplishment of a complete digestive process of human stomach is regulated by a spatio-temporally-coordinated electric pattern called gastric myoelectrical activity (GMA). The normal patterns of GMA present temporal evolution from endogenous rhythmic oscillation to bursting of spikes associated with contractions, and also ordered spatial propagation of the oscillating waves. The abnormal patterns of GMA have been observed in temporal dysrhythmia, such as tachygastria, bradygastria and arrhythmia, and in spatial propagation failure, such as retrograde propagation and uncoupling. Different GMA patterns are associated with different gastric symptoms and there exist some nonlinear mechanisms to govern the formation and dynamic evolution of these patterns. However, these mechanisms are so complex that few of them are known by medical observations. The aim of this study is to explore these mechanisms by spatio-temporal modeling of GMA. The single-cell model simulating the formation process of slow waves and spikes, the multi-cell model simulating the propagation process of GMA and the extracellular model simulating the formation of bipolar recordings are presented.

Graeco-Latin squares design for line detection in the presence of correlated noise

In this paper, the problem of detecting narrow lines embedded in correlated noise is investigated. An approach based on the contrast theory is adapted to the four-way Graeco-Latin squares design. The analysis provides a theoretical basis for the comparison of a line detector to other detectors that ignore noise dependence. A new and compensated algorithm is developed for detecting lines oriented in any major direction in a two-dimensional image plane. The four-way design is also shown to remove any background obscuration, and the actual processor is robust, simple, efficient, and suitable for real-time applications. Extensive computer simulations demonstrate the performance of the proposed detector relative to some classical mask-based detectors.

In situ SR function in postinfarction myocytes

Previous studies have shown lower systolic intracellular Ca(2+) concentrations ([Ca(2+)](i)) and reduced sarcoplasmic reticulum (SR)-releasable Ca(2+) contents in myocytes isolated from rat hearts 3 wk after moderate myocardial infarction (MI). Ca(2+) entry via L-type Ca(2+) channels was normal, but that via reverse Na(+)/Ca(2+) exchange was depressed in 3-wk MI myocytes. To elucidate mechanisms of reduced SR Ca(2+) contents in MI myocytes, we measured SR Ca(2+) uptake and SR Ca(2+) leak in situ, i.e., in intact cardiac myocytes. For sham and MI myocytes, we first demonstrated that caffeine application to release SR Ca(2+) and inhibit SR Ca(2+) uptake resulted in a 10-fold prolongation of half-time (t(1/2)) of [Ca(2+)](i) transient decline compared with that measured during a normal twitch. These observations indicate that early decline of the [Ca(2+)](i) transient during a twitch in rat myocytes was primarily mediated by SR Ca(2+)-ATPase and that the t(1/2) of [Ca(2+)](i) decline is a measure of SR Ca(2+) uptake in situ. At 5.0 mM extracellular Ca(2+), systolic [Ca(2+)](i) was significantly (P </= 0.05) lower (337 +/- 11 and 416 +/- 18 nM in MI and sham, respectively) and t(1/2) of [Ca(2+)](i) decline was significantly longer (0.306 +/- 0.014 and 0.258 +/- 0.014 s in MI and sham, respectively) in MI myocytes. The 19% prolongation of t(1/2) of [Ca(2+) ](i) decline was associated with a 23% reduction in SR Ca(2+)-ATPase expression (detected by immunoblotting) in MI myocytes. SR Ca(2+) leak was measured by a novel electrophysiological technique that did not require assigning empirical constants for intracellular Ca(2+) buffering. SR Ca(2+) leak rate was not different between sham and MI myocytes: the time constants of SR Ca(2+) loss after thapsigargin were 290 and 268 s, respectively. We conclude that, independent of decreased SR filling by Ca(2+) influx, the lower SR Ca(2+) content in MI myocytes was due to reduced SR Ca(2+) uptake and SR Ca(2+)-ATPase expression, but not to enhanced SR Ca(2+) leak.

Monte Carlo calculated output factors of a Leksell Gamma Knife unit

The Leksell Gamma Knife is a standard radiosurgical tool for treating brain lesions by directing beams of gamma radiation to a specific region. The diameter of the gamma beams is confined by collimator systems and available collimator sizes are 4, 8, 14 and 18 mm. The reduction in dose rate for each collimator helmet is called the output factor (OPF). Experimental determination of OPFs is difficult due to the extremely narrow beams for which the dose is determined. In the present work, the PRESTA version of the EGS4 Monte Carlo code was used to obtain relative OPFs for the Leksell Gamma Knife for collimator sizes of 14, 8 and 4 mm (relative to that of the 18 mm collimator). A spherical probe with a radius of 1 mm was utilized in this computer experiment. Our Monte Carlo results gave OPFs of 0.974, 0.951 and 0.872 for the 14 mm, 8 mm and 4 mm collimators respectively, relative to the 18 mm collimator. Our calculated OPF for the 4 mm collimator helmet was more than 8% higher than the value currently used, but in good agreement with the average of experimental values obtained by various Gamma Knife centres throughout the world and with the value now recommended by the manufacturer, Elekta (Elekta Instrument AB, Skeppargatan 8, S-114 52 Stockholm, Sweden).

Rapid simultaneous comparison system for subjective grading scales grading scales for facial paralysis

OBJECTIVE

The senior authors developed a computer-assisted rapid, simultaneous comparison system for nine international grading scales for facial paralysis. The purpose of this study is to present the system and to compare the agreement of hand-performed House-Brackmann and Sunnybrook scales, two frequently used scales herein taken as the concurrent criterion test standards, with those like scales done simultaneously in the computed system.

STUDY DESIGN

The study design was a prospective concurrent criterion validity study. Test-retest reliability and interobserver agreement were assessed using the kappa statistic (k) for ordinal data and the intraclass correlation coefficient (ICC) for semidimensional data.

SETTING

The study was conducted at a university practice.

PATIENTS

Ten consecutive consenting subjects with varying degrees of facial paralysis were studied.

INTERVENTION

Each subject was measured, in random order, twice by each method by each of two independent observers.

MAIN OUTCOME MEASURES

House-Brackmann score, Sunnybrook score, and like-scale scores done simultaneously in the computed system were measured.

RESULTS

Agreement between the computed system and hand-performed criterion standards was equal to each scale compared against itself; for the House-Brackmann, agreement was moderate (k = 0.554); for the Sunnybrook, agreement was excellent (ICC = 0.976).

CONCLUSIONS

The computed system has the advantage of allowing an examiner to view a rapid, simultaneous display of multiple grading scale scores at a keystroke from one clinical assessment input, obviating the labor of repeating measures by hand.

Identification of the erythropoietin receptor domain required for calcium channel activation

Erythropoietin (Epo) activates a voltage-independent Ca2+ channel that is dependent on tyrosine phosphorylation. To identify the domain(s) of the Epo receptor (Epo-R) required for Epo-induced Ca2+ influx, Chinese hamster ovary (CHO) cells were transfected with wild-type or mutant Epo receptors subcloned into pTracer-cytomegalovirus vector. This vector contains an SV40 early promoter, which drives expression of the green fluorescent protein (GFP) gene, and a cytomegalovirus immediate-early promoter driving expression of the Epo-R. Successful transfection was verified in single cells by detection of GFP, and intracellular Ca2+ ([Ca]i) changes were simultaneously monitored with rhod-2. Transfection of CHO cells with pTracer encoding wild-type Epo-R, but not pTracer alone, resulted in an Epo-induced [Ca]i increase that was abolished in cells transfected with Epo-R F8 (all eight cytoplasmic tyrosines substituted). Transfection with carboxyl-terminal deletion mutants indicated that removal of the terminal four tyrosine phosphorylation sites, but not the tyrosine at position 479, abolished Epo-induced [Ca]i increase, suggesting that tyrosines at positions 443, 460, and/or 464 are important. In CHO cells transfected with mutant Epo-R in which phenylalanine was substituted for individual tyrosines, a significant increase in [Ca]i was observed with mutants Epo-R Y443F and Epo-R Y464F. The rise in [Ca]i was abolished in cells transfected with Epo-R Y460F. Results were confirmed with CHO cells transfected with plasmids expressing Epo-R mutants in which individual tyrosines were added back to Epo-R F8 and in stably transfected Ba/F3 cells. These results demonstrate a critical role for the Epo-R cytoplasmic tyrosine 460 in Epo-stimulated Ca2+ influx.

Monte Carlo calculations and GafChromic film measurements for plugged collimator helmets of Leksell Gamma Knife unit

The Monte Carlo technique and GafChromic films were employed to verify the accuracy of the dose planning system (Leksell GammaPlan) used in Gamma Knife (type B) radiosurgery when plugged collimator helmets were used. The EGS4 Monte Carlo code was used to calculate the dose distribution along the x, y, and z axes when a single shot was delivered at the center point (unit center point: x = 100, y = 100, z = 100) of a spherical polystyrene phantom, with gamma angle of 90 degrees. Two different sizes of the plugged collimator helmets, 4 and 18 mm, were studied. Two typical plugged patterns, 51 plugs and 99 plugs along the y direction, were examined. The results of our Monte Carlo trials showed good consistency with GammaPlan calculations and GafChromic film measurements. Furthermore, the Monte Carlo results showed that radiation leakage from the plugs was too small to affect the overall isodose curve distribution even when the heavily plugged pattern of up to 99 plugs was employed. The results of this project provide confidence to all Gamma Knife centers using the Leksell GammaPlan treatment planning system.

Effects of impaired Ca2+ homeostasis on contraction in postinfarction myocytes

The significance of altered Ca2+ influx and efflux pathways on contractile abnormalities of myocytes isolated from rat hearts 3 wk after myocardial infarction (MI) was investigated by varying extracellular Ca2+ concentration ([Ca2+]o, 0.6-5.0 mM) and pacing frequency (0.1-5.0 Hz). Myocytes isolated from 3-wk MI hearts were significantly longer than those from sham-treated (Sham) hearts (125 +/- 1 vs. 114 +/- 1 micrometer, P < 0.0001). At high [Ca2+]o and low pacing frequency, conditions that preferentially favored Ca2+ influx over efflux, Sham myocytes shortened to a greater extent than 3-wk MI myocytes. Conversely, under conditions that favored Ca2+ efflux (low [Ca2+]o and high pacing frequency), MI myocytes shortened more than Sham myocytes. At intermediate [Ca2+]o and pacing frequencies, differences in steady-state contraction amplitudes between Sham and MI myocytes were no longer significant. Collectively, the interpretation of these data was that Ca2+ influx and efflux pathways were subnormal in MI myocytes and that they contributed to abnormal cellular contractile behavior. Because Na+/Ca2+ exchange activity, but not whole cell Ca2+ current, was depressed in 3-wk MI rat myocytes, our results on steady-state contraction are consistent with, but not proof of, the hypothesis that depressed Na+/Ca2+ exchange accounted for abnormal contractility in MI myocytes. The effects of depressed Na+/Ca2+ exchange on MI myocyte mechanical activity were further evaluated in relaxation from caffeine-induced contractures. Because Ca2+ uptake by sarcoplasmic reticulum was inhibited by caffeine and with the assumption that intracellular Na+ and membrane potential were similar between Sham and MI myocytes, myocyte relaxation from caffeine-induced contracture can be taken as an estimate of Ca2+ extrusion by Na+/Ca2+ exchange. In MI myocytes, in which Na+/Ca2+ exchange activity was depressed, the half time of relaxation (1.54 +/- 0.14 s) was significantly (P < 0.02) prolonged compared with that measured in Sham myocytes (1.10 +/- 0.10 s).

Blind separation of multichannel electrogastrograms using independent component analysis based on a neural network

The electrogastrogram (EGG) is an abdominal surface measurement of gastric myo-electrical activity which regulates gastric contractions. It is of great clinical importance to record and analyse multichannel EGGs, which provide more information on the propagation and co-ordination of gastric contractions. EGGs are, however, contaminated by myo-electric interference from other organs and artefacts such as motion and respiration. The aim of the study is to separate the gastric signal from noisy multichannel EGGs without any information on the interference, using independent component analysis. A neural-network model is proposed, and corresponding unsupervised learning algorithms are developed to achieve the separation. The performance of the proposed method is investigated using artificial data simulating real EGG signals. Experimental EGG data are obtained from humans and dogs. The processed results of both simulated and real EGG data show the following: first, the proposed method is able to separate normal gastric slow waves from respiratory artefacts and random noises. It is also able to extract gastric slow waves, even when the EGG is contaminated by severe respiratory and ECG artefacts. Secondly, when the stomach contains various gastric electric signals with different frequencies, the proposed method is able to separate these different signals, as illustrated by simulations. These data suggest that the proposed method can be used to separate gastric slow waves, respiratory and motion artefacts, and intestinal myo-electric interference that are mixed in the EGG. It can also be used to detect gastric slow-wave uncoupling, during which the stomach has multiple gastric signals with different frequencies. It is believed that the proposed method may also be applicable to other biomedical signals.

'Tweaked' GammaPlan for target volume measurement in non-fiducial based images: a simple routine for follow-up assessment

The GammaPlan provides accurate estimation of target volume. However, a stereotactic frame and fiducials are required. At follow-up MR/CT, fiducials are no longer available. Surgeons rely on visual impression, 2-D measurements, or other methods to estimate the volume of the treated targets. These methods are not objective and may give rise to misleading conclusions. By modifying the image header files of GammaPlan version 3, it is possible to scale the images which are not acquired with stereotactic fiducials. The target is then mapped and its volume measured as usual. The target volumes in 7 patients were measured by the tweaked GammaPlan and compared with volume measurements using the standard version. The mean error was less than 2%. In a separate study, phantom syringes with known volumes of water were used for MR imaging. The tweaked version again gave accurate volume estimation of the phantom syringes with a less than 5% error for most cases. This method has subsequently been used in all Gamma Knife follow-up cases. Significant volume changes have been detected where conventional assessment showed no apparent change. Moreover, such volume changes correlated with clinical improvement or deterioration. It is recommended that all Gamma Knife users report tumor response by volume change. Our method is simple, reliable and does not require additional cost.

Endurance exercise alters the contractile responsiveness of rat heart to extracellular Na+ and Ca2+

PURPOSE AND METHODS

The isovolumic contractile responsiveness of left ventricular (LV) myocardium to altered extracellular [Ca2+], [Na+], and pacing frequency was examined using perfused hearts (37 degrees C) isolated from sedentary (SED) and treadmill-trained (TR) adult female rats.

RESULTS

The suppressive effect of reducing perfusate free [Ca2+] to 0.7 mM on LV developed pressure (delta LVP) was greater in the TR hearts compared with SED hearts (P < 0.05). When perfusate [Na+] was reduced to 120 mM ([Ca2+] = 0.7 mM), delta LVP augmentation was greatest in the TR hearts (P < 0.05). The negative force-frequency relationship observed at physiologic [Ca2+] and [Na+] was progressively altered toward a positive force-frequency relationship with each subsequent change in perfusate [Ca2+] and [Na+] although the effect was greatest in TR hearts (P < 0.05).

CONCLUSIONS

Training elicited a small but significant (P < 0.05) prolongation in the pressure development phase of contraction. Under the physiological [Ca2+], [Na+] perfusion condition, training produced an increase in the magnitude of extrasystolic potentiation of LV pressure, whereas the time constant of mechanical restitution was unaffected. Training affected neither the Ca(2+)-dependence nor the maximal capacity of [3H] ryanodine binding to LV myocardial homogenates. The simplest interpretation of [Na+] and [Ca2+] reduction experiments is that myocardial Ca2+ efflux was augmented by exercise training.

Monte Carlo calculation of single-beam dose profiles used in a gamma knife treatment planning system

The accuracy of single-beam dose profiles used in the algorithm of the Gamma Knife treatment planning system (Leksell GammaPlan) is verified. EGS4 Monte Carlo calculation was employed to calculate the dose distributions of single-beams in a spherical water phantom with diameter 160 mm. The beams were directed to the center of the phantom. Collimators of 4, 8, 14, and 18 mm sizes were studied. The single-beam dose profiles provided by Elekta (Manufacturer of Leksell Gamma Knife) were excellently consistent with the results of Monte Carlo for the 4, 14, and 18 mm collimators. The maximum discrepancy was less than 3% at all radial distances. For the 8 mm collimator, the maximum discrepancy was 8% in the relative dose in the radial distance range from 4.3 mm to 5.2 mm. Excellent agreement in dose profiles along x, y, and z axes for all collimator helmets by summing over all 201 sources was observed between the cases using the default single-beam dose profiles and the calculated Monte Carlo results, except for the 8 mm collimator helmet along z axis. Such difference may however be too small to give a clinical significance.

Diagnosis and radioablation treatment of toxic multinodular goiter in a hemodialysis patient

Toxic multinodular goiter is rare in hemodialysis patients. In addition, establishing the diagnosis of hyperthyroidism in the elderly patient with renal failure is difficult because abnormal thyroid function tests can erroneously be attributed to euthyroid sick syndrome. Treatment of hyperthyroidism in dialysis patients by radioiodine ablation involves careful calculation of 131I dose, determination of interval between 131I administration and its removal by hemodialysis, and minimization of radiation hazards during dialytic removal of 131I. We described the clinical presentation of an elderly dialysis patient with toxic multinodular goiter and discussed our diagnostic and therapeutic approaches. The patient's recovery after 131I ablation was complete and uneventful.

Response of isolated rat descending vasa recta to bradykinin

Outer medullary descending vasa recta (OMDVR) were dissected from the outer medullary vascular bundles of young rats, perfused in vitro, and loaded with fura 2 for measurement of intracellular calcium concentration ([Ca2+]i) by fluorescent ratio imaging. Fluorescent video images revealed that fura 2 selectively loads into endothelial cells but not pericytes. Bradykinin (BK), at concentrations > 10(-11) M, elicited an increase in [Ca2+]i from baseline values in the range from 50 to 100 nM to peak values of 600-800 nM followed by a sustained plateau of 150-250 nM. The vasopressin V1-receptor agonist [Phe2,Ile3,Orn8]vasopressin constricted OMDVR but yielded no observable [Ca2+]i response, a finding that is consistent with an endothelial cell origin for the fura 2 fluorescent signal. The BK [Ca2+]i response was blocked by the selective BK B2-receptor antagonists D-Arg-[Hyp3,Thi5.8,D-Phe7]BK and D-Arg-[Hyp3,D-Phe7,Leu8]BK but not the B1 antagonist des-Arg9-[Leu8]BK. BK vasodilated microperfused OMDVR that had been preconstricted with 10(-8) M angiotensin II. We conclude that the [Ca2+]i response of OMDVR endothelia can be selectively studied with fura 2, that BK increases endothelial [Ca2+]i via the B2 receptor, and that BK can vasodilate descending vasa recta.

Sprint training attenuates myocyte hypertrophy and improves Ca2+ homeostasis in postinfarction myocytes

Myocytes isolated from rat hearts 3 wk after myocardial infarction (MI) had decreased Na+/Ca2+ exchange currents (I Na/Ca; 3 Na+ out:1 Ca2+ in) and sarcoplasmic reticulum (SR)-releasable Ca2+ contents. These defects in Ca2+ regulation may contribute to abnormal contractility in MI myocytes. Because exercise training elicits positive adaptations in cardiac contractile function and myocardial Ca2+ regulation, the present study examined whether 6-8 wk of high-intensity sprint training (HIST) would ameliorate some of the cellular maladaptations observed in post-MI rats with limited exercise activity (Sed). In MI rats, HIST did not affect citrate synthase activities of plantaris muscles but significantly increased the percentage of cardiac alpha-myosin heavy chain (MHC) isoforms (57.2 +/- 1.9 vs. 49.3 +/- 3.5 in MI-HIST vs. MI-Sed, respectively; P < or = 0.05). At the single myocyte level, HIST attenuated cellular hypertrophy observed post-MI, as evidenced by reductions in cell lengths (112 +/- 4 vs. 130 +/- 5 micrograms in MI-HIST vs. MI-Sed, respectively; P < or = 0.005) and cell capacitances (212 +/- 8 vs. 242 +/- 9 pF in MI-HIST vs. MI-Sed, respectively; P < or = 0.015). Reverse I Na/Ca was significantly lower (P < or = 0.0001) in myocytes from MI-Sed rats compared with those from rats that were sham operated and sedentary. HIST significantly increased reverse I Na/Ca (P < or = 0.05) without affecting the amount of Na+/Ca2+ exchangers (detected by immunoblotting) in MI myocytes. SR-releasable Ca2+ content, as estimated by integrating forward I Na/Ca during caffeine-induced SR Ca2+ release, was also significantly increased (P < or = 0.02) by HIST in MI myocytes. We conclude that the enhanced cardiac output and stroke volume in post-MI rats subjected to HIST are mediated, at least in part, by reversal of cellular maladaptations post-MI.

Endurance training does not affect intrinsic calcium current characteristics in rat myocardium

The voltage-dependent Ca2+ channel (L-type channel) controls an inward Ca2+ current (ICa) that is centrally involved in the regulation of myocardial excitation-contraction (EC) coupling. A significant body of evidence exists to support the idea that exercise training elicits alterations in myocardial Ca2+ regulation, and the L-type channel has been implicated as a possible site of adaptation. The purpose of this study was to determine whether training elicits adaptations at the level of the L-type Ca2+ channel, as reflected by alterations in whole cell ICa characteristics in single myocytes isolated from rat left ventricle (LV). Female rats were treadmill trained at a moderately high intensity for a minimum of 20 wk. Body weight was unaffected by the training protocol, whereas there was a trend (P = 0.06) for a modest increase in LV weight (approximately 8%). Training produced significant (P < 0.05) increases in mean myocyte capacitance (approximately 9%) and myocyte length (approximately 6%), thus providing electrophysiological and morphological evidence that training elicited LV cardiocyte hypertrophy. Whole cell ICa vs. voltage and ICa density vs. voltage relationships as well as ICa inactivation and recovery characteristics were unaffected by our training paradigm. These findings do not support the hypothesis that training elicits adaptations in L-type Ca2+ channel number or intrinsic function in a model exhibiting classical exercise training-induced myocardial hypertrophy. Our results do not, however, preclude the possibility that training-induced adaptations at sites other than the L-type Ca2+ channel could affect ICa and myocardial EC coupling.

Detection and deletion of motion artifacts in electrogastrogram using feature analysis and neural networks

Electrogastrogram is a surface measurement of gastric myoelectrical activity, and electrogastrography has been an attractive method for physiological and pathophysiological studies of the stomach due to its noninvasive nature. Motion artifacts, however, ruin the electrogastrogram (EGG), and make the analysis very difficult and sometimes even impossible. They must be eliminated from EGG signals before analysis. Up to now, this can only be done by visual inspection, which is not only time-consuming but also subjective. In this study, a method using feature analysis and neural networks has been developed to realize automatic detection and elimination of the motion artifacts in EGG recordings by computer. Experiments were conducted to investigate the characteristics of different motion artifacts. Useful features were extracted, and different combinations of the features used as the input of the neural network were compared to obtain the optimal performance for the detection of motion artifacts using the artificial neural network.

Hypertension alters rapid cooling contractures in single rat cardiocytes

Previous work has demonstrated that, in single, paced left ventricular (LV) myocytes isolated from rats with hypertension, the extent of myocyte shortening and the amplitude of the cytosolic Ca2+ concentration transient are decreased relative to normal myocytes. These findings suggest that reduced sarcoplasmic reticular (SR) Ca2+ release could be responsible for hypertension-induced attenuation of the myocyte contractile response. Hypertension-induced reductions in SR Ca2+ release could be due to 1) a decrease in releasable SR Ca2+ content relative to the sarcoplasmic volume into which it is released or 2) alterations in the SR Ca2+ release mechanism such that the fractional release of SR Ca2+ is reduced. Using rapid cooling contractures (RCCs) to provide an index of SR Ca2+ content, we conducted a series of experiments designed to test the former hypothesis. Single LV myocytes were isolated from normotensive control rats and from rats with hypertension, which was induced by abdominal aortic banding (for approximately 4 mo). The extent of myocyte shortening during an RCC is taken to be directly proportional to SR Ca2+ content. As expected, the amplitudes of both twitches and RCCs decreased as pacing frequency increased from 0.2 to 1.0 Hz across both control and hypertensive groups, although the effect was greatest in control myocytes. A significant finding of this study was that, at both pacing frequencies, RCC magnitude was attenuated in hypertensive relative to control myocytes. These results suggest that in hypertension cellular Ca2+ homeostasis is altered and there is a mismatch between releasable SR Ca2+ content and the sarcoplasmic volume into which it is released.

Modulation of calcium channels in human erythroblasts by erythropoietin

Erythropoietin (Epo) induces a dose-dependent increase in intracellular free Ca2+ ([Ca2+]i) in human erythroblasts, which is dependent on extracellular Ca2+ and blocked by high doses of nifedipine or Ni2+. In addition, pretreatment of human erythroblasts with mouse antihuman erythropoietin receptor antibody but not mouse immunopure IgG blocked the Epo-induced [Ca2+]i increase, indicating the specificity of the Ca2+ response to Epo stimulation. In this study, the erythropoietin-regulated calcium channel was identified by single channel recordings. Use of conventional whole cell patch-clamp failed to detect Epo-induced whole cell Ca2+ current. To minimize washout of cytosolic constituents, we next used nystatin perforated patch, but did not find any Epo-induced whole cell Ca2+ current. Using Ba2+ (30 mmol/L) as charge carrier in cell-attached patches, we detected single channels with unitary conductance of 3.2 pS, reversal potential of +72 mV, and whose unitary current (at +10 mV) increased monotonically with increasing Ba2+ concentrations. Channel open probability did not appreciably change over the voltage range (-50 to +30 mV) tested. Epo (2 U/mL) increased both mean open time (from 4.27 +/- 0.75 to 11.15 +/- 1.80 ms) and open probability (from 0.26 +/- 0.06 to 2.56 +/- 0.59%) of this Ba(2+)-permeable channel. Our data strongly support the conclusion that the Epo-induced [Ca2+]i increase in human erythroblasts is mediated via Ca2+ entry through a voltage-independent Ca2+ channel.

Na+/Ca2+ exchange currents and SR Ca2+ contents in postinfarction myocytes

Myocytes isolated from rat hearts 3 wk after myocardial infarction (MI) had lower peak cytosolic free Ca2+ concentration ([Ca2+]i) and reduced maximal extent of cell shortening during contraction, but Ca2+ entry via L-type Ca2+ channels was normal. In the current study using whole cell patch-clamp technique, reverse Na+/Ca2+ exchange current (INa/Ca; 3 Na+ out:1 Ca2+ in) was measured in myocytes in which Na+, K+, and Ca2+ currents were blocked or minimized. Steady-state outward currents measured under these conditions increased with depolarization or with elevation of extracellular Ca2+ concentration ([Ca2+]o) from 1.8 to 5.0 mM, but were inhibited by 5 mM Ni2+ or by reduction of [Ca2+]i to near zero. In addition, reduction of cytosolic free Na+ concentration or of [Ca2+]i also decreased the amplitude of the outward current. These characteristics indicate the outward current was INa/Ca operating in reverse mode. Reverse INa/Ca was significantly lower in MI myocytes, especially at more positive voltages. In addition, sarcoplasmic reticulum (SR)-releasable Ca2+ content as estimated by integrating forward INa/Ca during caffeine-induced SR Ca2+ release was also significantly lower in MI myocytes. Depressed Na+/Ca2+ exchange activity may contribute to abnormal [Ca2+]i dynamics in MI myocytes.

A radiological approach to the through and through technique for percutaneous passage of ureteric strictures

Some ureteric strictures are so tight that they are difficult to traverse with balloon catheters or internal stents. We present five such cases, which were traversed using a modified through and through technique with a hydrophilic coated guide-wire. The reasons for the difficulty are discussed, and the merits of the modified technique compared with conventional techniques are described.

G-protein alpha subunit Gi(alpha)2 mediates erythropoietin signal transduction in human erythroid precursors

Erythropoietin induces a dose-dependent increase in cytosolic calcium in human erythroblasts that is mediated by a voltage-independent Ca2+ channel. Inhibition of this response to erythropoietin by pertussis toxin suggests involvement of guanine nucleotide-binding regulatory proteins (G-proteins). The role of G-proteins in regulation of the erythropoietin-modulated Ca2+ channel was delineated here by microinjection of G-protein modulators or subunits into human erythroid precursors. This is the first report on the use of microinjection to study erythropoietin signal transduction in normal precursor cells. Fura-2 loaded day-10 burst-forming units-erythroid-derived erythroblasts were used for microinjection and free intracellular calcium concentration ([Ca(i)]) was measured with digital video imaging. BCECF (1,2',7'-bis(2-carboxyethyl)-5-(and -6-)-carboxyfluorescein) was included in microinjectate, and an increase in BCECF fluorescence was evidence of successful microinjection. Cells were microinjected with nonhydrolyzable analogues of GTP, GTPgammaS or GDPbetaS, which maintain the alpha subunit in an activated or inactivated state, respectively. [Ca(i)] increased significantly in a dose-dependent manner after microinjection of GTPgammaS. However, injection of GDPbetaS blocked the erythropoietin-induced calcium increase, providing direct evidence that activation of a G-protein is required. To delineate which G-protein subunits are involved, alpha or betagamma transducin subunits were purified and microinjected as a sink for betagamma or alpha subunits in the erythroblast, respectively. Transducin betagamma, but not alpha, subunits eliminated the calcium response to erythropoietin, demonstrating the primary role of the alpha subunit. Microinjected antibodies to Gi(alpha)2, but not Gi(alpha)1 or Gi(alpha)3, blocked the erythropoietin-stimulated [Ca(i)] rise, identifying Gi(alpha)2 as the subunit involved. This was confirmed by the ability of microinjected recombinant myristoylated Gi(alpha)2, but not Gi(alpha)1 or Gi(alpha)3 subunits, to reconstitute the response of pertussis toxin-treated erythroblasts to erythropoietin. These data directly demonstrate a physiologic function of G-proteins in hematopoietic cells and show that Gi(alpha)2 is required in erythropoietin modulation of [Ca(i)] via influx through calcium channels.

Quantitative assessment of the variation within grades of facial paralysis

A completely objective, unambiguous outcome measure of facial function is now available. A new automated computer-assisted clinimetric system combines the crucial detection capabilities of the human observer and the unique capacity of the computer to quantify the image light reflectance difference observed during facial expression. The new system was applied to 27 patients with a variety of diseases affecting the facial nerve. All subjects could be individually and objectively ranked, and disease-specific profiles could be constructed. These tasks are not possible with the House-Brackmann scale, because of the wide variation within grades and the ambiguity between grades. With the automated objective, unambiguous outcome measure, it may be possible to define individual case progression, recovery, and outcome over the course of disease.

Regulation of rDNA transcription during endothelin-1-induced hypertrophy of neonatal cardiomyocytes. Hyperphosphorylation of upstream binding factor, an rDNA transcription factor

Treatment of cultured neonatal cardiomyocytes with endothelin-1 and phorbol 12-myristate 13-acetate (PMA) results in cardiomyocyte hypertrophy. However, the signal transduction pathways involved in this process are poorly understood. Because increased ribosome biogenesis is a requisite for hypertrophy, we sought to (1) confirm the hypothesis that these two hypertrophic agents did indeed induce rRNA synthesis and (2) examine the mechanism through which this induction was accomplished. In this study, hypertrophy of contraction-arrested neonatal cardiomyocytes induced by treatment with either endothelin-1 or PMA was associated with increased rDNA transcription. Western blots demonstrated that the enhanced rates of rDNA transcription were not mediated by increased amounts of either RNA polymerase I or upstream binding factor (UBF), an rDNA transcription factor. However, immunoprecipitation of [32P] orthophosphate-labeled UBF from hypertrophying neonatal cardiomyocytes suggested that the increased rate of rDNA transcription may be due to the hyperphosphorylation of UBF, which would increase the activity of UBF. The increase in UBF phosphorylation occurred within 3 to 6 hours after exposure to either agent, was maximal at 12 hours, and was sustained for at least the first 24 hours of exposure. Phosphoamino acid analysis of UBF immunoprecipitated from control and treated cardiomyocytes demonstrated that UBF was phosphorylated exclusively on serine residues. Our previous studies have shown that the cellular UBF content increased in adrenergic- and contraction-induced models of cardiac hypertrophy. This study with endothelin-1 and PMA demonstrates that the modulation of UBF phosphorylation is an additional pathway by which ribosome biogenesis may be regulated in neonatal cardiomyocytes. These results support the hypothesis that UBF is an important regulatory factor during the initiation and maintenance of the accelerated rate of rDNA transcription observed during neonatal cardiomyocyte hypertrophy mediated by both phorbol esters and endothelin-1.

Calcium currents in postinfarction rat cardiac myocytes

Myocytes isolated from rat hearts that have suffered 35% myocardial infarction (MI) 3 wk prior have lower peak cytosolic Ca2+ concentration ([Ca2+]i) during contraction compared with Sham myocytes, a difference that is amplified by isoproterenol or high extracellular Ca2+ concentration ([Ca2+]o). To evaluate whether reduced [Ca2+]i in MI myocytes is due to decreased Ca2+ entry, we measured [3H]PN-200-110 [dihydropyridine (DHP)] binding and whole cell Ca2+ current (ICa). DHP binding decreased in both sarcolemmal vesicles and intact myocytes from hearts 3 wk after MI. In contrast, ICa was not different between Sham and MI myocytes incubated at 1.8 mM [Ca2+]o. At 5.0 mM [Ca2+]o, ICa increased similarly in Sham and MI myocytes. Steady-state voltage dependence of activation and inactivation were similar between Sham and MI myocytes, as were the fast- and slow-inactivation time constants. Isoproterenol (1 microM) significantly increased ICa in Sham but not in MI myocytes. Forskolin (10 microM) dibutyryl adenosine 3',5'-cyclic monophosphate (5 mM) significantly increased ICa in MI myocytes; the magnitude of ICa increase was similar to that observed in Sham myocytes. We conclude that 1) decreased systolic [Ca2+]i in MI myocytes was not due to reduced Ca2+ entry via L-type Ca2+ channels; 2) discrepancy between DHP binding (decrease) and ICa (no change) results may be explained by higher channel availability and/or increased long-opening modes (mode 2) in MI myocytes; 3) reduction in isoproterenol-induced [Ca2+]i increase in MI myocytes was partly due to decreased ICa, resulting in less Ca2+ release from sarcoplasmic reticulum; 4) the adenylate cyclase-protein kinase A signal-transduction pathway functioned normally in MI myocytes; and 5) decreased beta-adrenergic responsiveness in MI myocytes was likely due to altered coupling by G proteins.

[Ca2+]i transients in hypertensive and postinfarction myocytes

Changes in intracellular calcium concentration ([Ca2+]i) in paced fura 2-loaded myocytes isolated from Sham, renovascular hypertensive (Hyp), and myocardial-infarcted (MI) rats were examined. Compared with controls, Hyp myocytes paced at physiological rates had similar systolic but elevated diastolic [Ca2+]i. By contrast, systolic [Ca2+]i was significantly lower and diastolic [Ca2+]i higher in MI myocytes. The different patterns of alterations in [Ca2+]i dynamics in Hyp and MI myocytes may partly explain predominantly diastolic dysfunction in hypertensive hearts and systolic dysfunction in hearts surviving MI. In the presence of 1 microM isoproterenol, both Hyp and MI myocytes had much lower systolic [Ca2+]i when compared with their respective controls. Isoproterenol restored the elevated diastolic [Ca2+]i in Hyp myocytes toward normal but had no effect on the intrinsic differences in diastolic [Ca2+]i between Sham and MI myocytes. The observation that isoproterenol lowers diastolic [Ca2+]i in Hyp myocytes toward normal may provide a cellular mechanism for the lack of efficacy of beta-adrenergic blockers to improve diastolic compliance in patients with hypertensive hypertrophic cardiomyopathy.

Inhibition of ligand-induced activation of epidermal growth factor receptor tyrosine phosphorylation by curcumin

We explored the regulation of epidermal growth factor (EGF)-mediated activation of EGF receptor (EGF-R) phosphorylation by curcumin (diferuloyl-methane), a recently identified kinase inhibitor, in cultured NIH 3T3 cells expressing human EGF-R. Treatment of cells with a saturating concentration of EGF for 5-15 min induced increased EGF-R tyrosine phosphorylation by 4- to 11-fold and this was inhibited in a dose- and time-dependent manner by up to 90% by curcumin, which also inhibited the growth of EGF-stimulated cells. There was no effect of curcumin treatment on the amount of surface expression of labeled EGF-R and inhibition of EGF-mediated tyrosine phosphorylation of EGF-R by curcumin was mediated by a reversible mechanism. In addition, curcumin also inhibited EGF-induced, but not bradykinin-induced, calcium release. These findings demonstrate that curcumin is a potent inhibitor of a growth stimulatory pathway, the ligand-induced activation of EGF-R, and may potentially be useful in developing anti-proliferative strategies to control tumor cell growth.

Hormone-regulated Ca2+ channel in rat hepatocytes revealed by whole cell patch clamp

An inward current responsible for hormone regulated Ca2+ entry has been identified in cultured rat hepatocytes using whole cell patch clamp. Addition of 20 nM vasopressin or of 100 microM ATP induced the inward current, which could be observed more clearly after blocking an outward K+ current. This large outward K+ current, which appeared after addition of vasopressin or ATP, could be blocked either by replacing K+ with Cs+ in the external medium and in the pipette solution, or by simply including 0.5 microM apamin in the K(+)-containing external medium. The outward current appears to be carried by a Ca2+ activated K+ channel. In the presence of apamin, hepatocytes pretreated with vasopressin in a Ca(2+)-free media reveal an inward current on addition of external Ca2+ (5 mM). The current could also be elicited by addition of vasopressin when cells are preincubated in the presence of 5 mM external Ca2+. No current is seen on addition of Ca2+ in the absence of vasopressin. Initially, the inward current was ca 200-300 pA at -60 mV, but it declined rapidly over 3 min to ca 20 pA. The current approached zero, as an asymptote at positive potential, and appeared to be somewhat inwardly rectifying. Additions of 5 mM Mn2+ or 5 mM Ba2+ in place of Ca2+ produced little or no current. An inhibitor of ER Ca(2+)-ATPase, thapsigargin, could also trigger the cascade of events leading to plasma membrane conductance of Ca2+. The data suggest that hormone-stimulated Ca2+ entry into hepatocytes is mediated by a Ca(2+)-release activated channel highly specific for Ca2+. This is the first demonstration of such a channel in hepatocytes, though similar ones have been described in mast cells, in vascular endothelial cells and T-lymphocytes.

Erythropoietin modulation of intracellular calcium: a role for tyrosine phosphorylation

We have reported that erythropoietin induces a dose-dependent increase in cytosolic calcium ([Cai]) in single human peripheral blood BFU-E derived erythroblasts which is specific for stage of differentiation and that this increase is modulated by erythropoietin through an ion channel permeable to Ca2+. Here, the role of protein phosphorylation in the increase in intracellular free calcium [Cai] stimulated by erythropoietin was studied with digital video imaging. Preincubation of day 10 erythroblasts with a broad inhibitor of serine/threonine and tyrosine kinases, staurosporine (100 nM), blocked the increase in [Cai] over 20 min following erythropoietin stimulation. However, erythropoietin-induced calcium influx was unaffected by preincubation of cells with specific inhibitions of protein kinase C (calphostin C) or the cAMP- or cGMP-dependent kinases (KT 5720, HA 1004), and [Cai] did not increase following stimulation with phorbol 12-myristate 13-acetate (PMA) or dibutyryl cAMP. These results suggest that neither protein kinase C nor protein kinase A mediate the erythropoietin-induced [Cai] increase. In contrast, preincubation with genistein, a tyrosine kinase inhibitor, blocked the erythropoietin induced increase in [Cai]. To further study calcium entry in erythroblasts, we determined mastoparan, a peptide from wasp venom, induced a dose-dependent rise in [Cai] in erythroblasts which required external calcium. Stimulation of erythroid precursors with 10 microM mastoparan resulted in an increase in [Cai] from 52 +/- 3 nM to 214 +/- 36 nM which peaked at 20 min. The mastoparan-induced [Cai] increase was also dependent on tyrosine phosphorylation since it was blocked by preincubation with genistein. These results demonstrate that both erythropoietin and mastoparan stimulate calcium entry by a mechanism which has a genistein sensitive step and suggest that tyrosine kinase activation is required for the rise in [Cai] to occur.

Steel factor affects SCL expression during normal erythroid differentiation

Steel factor is one of the growth factors that controls the proliferation and differentiation of hematopoietic cells and SCL, also known as Tcl-5 or Tal-1, is a transcription factor involved in erythropoiesis. In this report, we studied the role of SCL in the proliferation of human peripheral blood burst-forming unit-erythroid (BFU-E) and the effects of Steel factor on SCL expression in proliferating erythroid cells. BFU-E-derived colonies increase progressively in size, as determined by cell number, from day 7 to day 14 of culture, with the greatest increase in colony size (10-fold expansion) occurring between day 7 and day 10. SCL protein levels in BFU-E-derived cells were highest in day 7 cells and decreased progressively from day 7 to day 14 of culture, suggesting an association of SCL with erythroid proliferation. In contrast, SCL mRNA levels did not decrease significantly between day 7 and day 14 cells, suggesting that posttranscriptional mechanisms are largely responsible for the decrease in SCL protein observed. The role of SCL in Steel factor-induced erythroid proliferation was then examined. In BFU-E-derived colonies cultured with Steel factor, colony size was significantly increased compared to control. In day 7 and day 10 erythroid precursors cultured with Steel factor, SCL protein was increased significantly compared to control. The increase in SCL protein levels in early erythroid precursors stimulated with Steel factor suggests one mechanism through which Steel factor may enhance normal erythroid proliferation. SCL mRNA levels assessed by Northern blot in day 7 cells did not increase significantly in response to Steel factor stimulation, suggesting that posttranscriptional mechanisms may also be important in the increase in SCL protein observed in response to Steel.

Ratiometric methodology for NAD(P)H measurement in the perfused rat heart using surface fluorescence

The surface fluorescence of the isolated perfused rat heart has been evaluated for the purpose of NAD(P)H quantitation. With the use of excitation at 340, 380, 415, and 430 nm with emission detection at 500 +/- 20 nm, the intensities at 340 and 380 nm excitation were found to be linearly related during NAD(P)H oxidation/reduction induced by changes in substrate availability. Changes in cardiac NAD(P)H caused similar changes at 340 and 380 nm excitation, but those at 340 nm were of greater magnitude. Isolated cardiac mitochondria exhibited essentially identical optical properties during changes in NAD(P)H content induced by changes in substrate availability and by NAD(H) oxidation/reduction caused by coupled phosphorylation of ADP. The changes in redox status of both isolated mitochondria and the intact perfused heart can be expressed by a 340/380 excitation fluorescence ratio because of these relationships. This value assumed a minimum and maximum value under conditions of complete oxidation and reduction, respectively. Use of this ratio in the perfused heart avoids the artifacts caused by cardiac motion and tissue stretch. Removal of motion artifacts with an excitation ratio could only be accomplished if the measurements at 340 and 380 nm were estimated at the same point in the cardiac cycle. A method of cardiac waveform reconstruction and signal averaging is described to obtain these data from sequential measurements. With these techniques, the reduction of cardiac NAD(P)H can be expressed as a percentage of the range obtained between minimum and maximum reduction. The described technique is of general utility in the assessment of cardiac bioenergetics.

Mechanisms of erythropoietin signal transduction: involvement of calcium channels

Erythropoietin (Epo) induces a dose-dependent increase in intracellular free calcium concentration ([Cai]) in single human BFU-E derived erythroblasts, which is specific for stage of differentiation and mediated through a voltage-independent ion channel permeable to calcium. This minireview examines the regulation of calcium channels by Epo during normal erythroid differentiation, as a model to delineate the immediate signaling events which follow interaction of Epo with its receptor.

Impaired cardiac function in rats with healed myocardial infarction: cellular vs. myocardial mechanisms

The inotropic responsiveness of isolated perfused rat hearts and single left ventricular (LV) myocytes to extracellular Ca2+ ([Ca2+]o) was examined 3 wk after ligation of left main coronary artery. Myocytes isolated from myocardial infarcted (MI) hearts were 10% longer. At [Ca2+]o of 1.1 mM, cell shortening as well as intracellular Ca2+ concentration dynamics were similar between MI and sham LV myocytes. At [Ca2+]o of 4.9 mM, maximal extent of cell shortening was significantly less in MI myocytes (16 +/- 1 vs. 22 +/- 1%), and peak intracellular Ca2+ concentration was also substantially lower. Thus, under conditions of high [Ca2+]o, decreased sarcolemmal Ca2+ influx and Ca2+ release during excitation-contraction may contribute to systolic dysfunction in MI hearts. Perfused working hearts and isovolumic heart preparations with infarcted LV displayed depressed maximal systolic pressure and decreased sensitivity to the inotropic effects of [Ca2+]o. Our data also indicate that, in addition to possible abnormalities in the contractile response of single myocytes, global factors such as loss of functional myocardium, altered chamber geometry, tissue fibrosis, and/or subendocardial ischemia contributed to depressed LV function in post-MI hearts perfused at physiological [Ca2+]o.

Variations in maximum amplitude of facial expressions between and within normal subjects

Definitive proof of efficacy of preventions and therapeutic interventions, and of risk factors in lower motor neuron facial paralyses continue to be confounded by the lack of repeatable quantitative measures of outcome. Clinical and research experience with human facial expression repeatedly demonstrates wide variations between subjects. To our knowledge, little information is available to isolate and describe the differences in dynamic facial expression between and within normal subjects. The purpose of this study is to use a statistical model to analyze the components of the observed variations of maximum amplitude measurement of image change during normal human subject facial expressions. Seventeen consecutive normal adult human subjects with no current or past evidence of facial nerve or ear disease were studied. Videotapes of command facial expressions were taken using specific and standardized conditions. The tapes were analyzed using a new computer-assisted image-change analysis program capable of generating dimensional data for the maximum amplitude of expression. These data were statistically analyzed using a General Linear Model with Nested variables to isolate and define component variations and errors. The General Linear Model predicted 88% of the observed total variation (p < 0.05).* A model performance this high suggests that most of the important independent variables were being studied. The major component of the variations was the difference among (between) subjects. Seventy-seven percent of the predicted variation was due to this difference (p < 0.05). Little of the variation (1%) seemed to be within-subjects. Test-retest agreement was acceptable.(ABSTRACT TRUNCATED AT 250 WORDS)