Predicted trends in the supply and demand of veterinarians in Japan

Currently in Japan, there are 32,000 active veterinarians, mainly engaged in small and large animal practice and public animal health and public health services. In the face of the notable increase in recent years in the proportion of female students enrolled in veterinary schools and in the number of households with companion animals, a model was developed to predict the supply and demand of veterinarians toward 2040 in Japan. Surveys were conducted on sampled households and veterinarians to estimate input variables used in the supply and demand model. From this data it is predicted that there might be somewhere between a shortage of 1,000 to an over-supply of 3,700 veterinarians engaged in small animal practice in 2040. This, however, will depend on possible changes in the number of visits made to veterinarians by small animal owners and the efficiency of practices in the future. The model also predicts that there will be a shortage of around 1,100 veterinarians in large animal practice in 2040. Considering the many assumptions made to estimate the input variables used in the model, the results of this study do not provide definitive conclusions, but provide a base for discussions on what will be needed in the veterinary profession in the future.

Isolation and characterization of resident macrophages from the smooth muscle layers of murine small intestine

Macrophages within the murine tunica muscularis were isolated and cultured for physiological studies. Following dispersion, macrophages were identified by phagocytotic activity of fluorescein isothiocyanate (FITC)-dextran. Immediately following isolation, macrophages were rounded and possessed fluorescent granula but developed a ramified shape after 3-4 days in culture. Resident and cultured macrophages were immunopositive for F4/80 and I-Ad/I-Ed. Greater than 90% of F4/80 positive cultured cells were FITC-dextran positive. Macrophages had resting membrane potentials (RMP) of -33.3 +/- 1.5 mV after 1 day in culture, which increased to -53.9 +/- 4.4 mV after 3-4 days. The change in RMP was associated with the development of an inward rectifying K+ current, and a decrease in a voltage-dependent, inactivating outward current. After 3-4 days in culture the inflammatory mediated substances adenosine triphosphate (ATP), platelet-activating factor and bacterial lipopolysaccharide induced increases in cytoplasmic Ca2+ ([Ca2+]i). Forskolin suppressed the ATP-induced increase in [Ca2+]i. Macrophages exhibited oxidative bursts, measured by oxidation of dihydrorhodamine-123 to rhodamine-123. Oxidative bursts coincided with a reduction in intracellular pH. Macrophages expressed a proton conductance that may participate in pH maintenance during reactive oxygen production. These results suggest that resident macrophages in the intestine may play a role in the immunological protection of the gut.

Increased smooth muscle contractility of intestine in the genetic null of the endothelin ETB receptor: a rat model for long segment Hirschsprung's disease

BACKGROUND AND AIMS

The endothelin ETB receptor null rat (ETB(-/-)R) has an intestinal segment without ganglia, and this rat is characterised by intestinal obstruction similar to that observed in human Hirschsprung's disease. In the present study, we have examined the myogenic mechanism responsible for obstruction in the ETB(-/-)R.

RESULTS

The ETB(-/-)R had an enlarged belly and the average lifespan was 18.1 days. The bowel from the rectum to the lower part of the small ileum was constricted whereas the upper region was dilated with faecal stasis and thus presented as megaileum. The constricted muscle segments without ganglia had a greater increase in absolute force when stimulated by carbachol, high K+, and endothelin-1 compared with that of normal siblings. In contrast, in the dilated part with ganglia, the absolute contractile force due to these stimulants in the ETB(-/-)R was not different from that in the ETB(+/+)R. Such a functional hypertrophy of the musculature was observed in parts of the colon, caecum, and distal ileum without ganglia but not in the part of the proximal ileum and jejunum with ganglia. Morphological study demonstrated that the thickness of the circular and longitudinal muscle layers was greater in the constricted part of the intestine in the ETB(-/-)R, and these changes were associated with an increase in the number of smooth muscle cells.

CONCLUSIONS

Our findings suggest that both increased contractility of smooth muscle and increased thickness of the intestinal muscular wall may contribute to the intestinal obstruction in the ETB(-/-)R.

Chronic effect of doxorubicin on vascular endothelium assessed by organ culture study

We have attempted to determine the chronic effects of doxorubicin, a commonly used anticancer agent, on vascular endothelium using an organ culture system. In rabbit mesenteric arteries treated with 0.3 microM doxorubicin for 7 days, rounding and concentrated nuclei and TUNEL-positive staining were observed in endothelial cells, indicating DNA damage and the induction of apoptosis. However, the endothelium-dependent relaxation induced by substance P and the expression of mRNA encoding endothelial NO synthase (eNOS) did not differ from those in control arteries. In arteries treated with a higher concentration (1 microM) of doxorubicin, apoptosis and damage to nuclei occurred in the endothelial cells at the third day of treatment, and the detachment and excoriation of endothelium from the tunica interna of the vascular wall were also observed. The impairment of endothelium-dependent relaxation was observed at the fifth day of the treatment with 1 microM doxorubicin. Additionally, apoptotic change in the smooth muscle layer was observed at this concentration of doxorubicin. Apoptotic phenomena were further confirmed by DNA fragmentation using isolated bovine aortic endothelial cells (BAECs) and A7r5 vascular smooth muscle cells, and it was revealed that BAECs are more sensitive than A7r5 to the apoptotic effect of doxorubicin. These results suggest that chronic treatment with doxorubicin at therapeutic concentrations induces apoptosis and excoriation of endothelial cells, which diminishes endothelium-dependent relaxation.

Contribution of chloride channel activation to the elevated muscular tone of the pulmonary artery in monocrotaline-induced pulmonary hypertensive rats

In monocrotaline-treated rat pulmonary artery from which endothelium was removed, greater spontaneous muscular tone was observed under resting conditions than in vehicle-treated artery. The aim of the present study was to show the possible contribution of Cl- channels in the mechanism of the elevated tone. Verapamil almost completely inhibited the elevated spontaneous muscular tone by decreasing [Ca2+]i. The elevated muscular tone was also inhibited by 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS), a Cl- channel inhibitor. After the inhibition of muscular tone by DIDS, verapamil did not induce further relaxation. Quantitative RT-PCR analysis indicated that the mRNA levels of ClC3 and Ca2+-activated Cl- channels did not change in the pulmonary hypertensive pulmonary artery from those of vehicle-treated rats. These results suggest that the elevated muscular tone observed in the monocrotaline-induced hypertensive pulmonary artery is due to membrane depolarization of smooth muscle cells and that this phenomenon might be mediated by the activation of DIDS-sensitive Cl- channels.

Hypoxia impairs endothelium-dependent relaxation in organ cultured pulmonary artery

In intrapulmonary arteries cultured under hypoxic conditions (5% oxygen) for 7 days, endothelium-dependent relaxation and cGMP accumulation induced by substance P were decreased as compared to those of a normoxic control (20% oxygen). In rabbit mesenteric arteries exposed to chronic hypoxia, however, endothelial dysfunction was not observed. Furthermore, in endothelium-denuded pulmonary arteries exposed to hypoxia, neither relaxation nor cGMP accumulation due to sodium nitroprusside differed from those of the normoxic control. Hypoxia did not change the mRNA expression of endothelial NO synthase (eNOS), the protein expression of eNOS or the eNOS regulatory protein caveolin-1 as assessed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) or whole-mount immunostaining. Morphological study revealed atrophy of endothelial cells and condensation of the eNOS protein in many cells. These results suggest that chronic hypoxia impaired NO-mediated arterial relaxation without changing either the eNOS protein expression or the NO-sensitivity of smooth muscle cells in pulmonary arteries. Changes in cell structure and organization may be involved in endothelial dysfunction.

Upregulation of iNOS by COX-2 in muscularis resident macrophage of rat intestine stimulated with LPS

We investigated the effect of lipopolysaccharide (LPS) on the induction of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in muscularis resident macrophages of rat intestine in situ. When the tissue was incubated with LPS for 4 h, mRNA levels of iNOS and COX-2 were increased. The majority of iNOS and COX-2 proteins appeared to be localized to the dense network of muscularis resident macrophages immunoreactive to ED2. LPS treatment also increased the production of nitric oxide (NO), PGE(2), and PGI(2). The increased expression of iNOS mRNA by LPS was suppressed by indomethacin but not by N(G)-monomethyl-L-arginine (L-NMMA). The increased expression of COX-2 mRNA by LPS was affected neither by indomethacin nor by L-NMMA. Muscle contractility stimulated by 3 microM carbachol was significantly inhibited in the LPS-treated muscle, which was restored by treatment of the tissue with L-NMMA, aminoguanidine, indomethacin, or NS-398. Together, these findings show that LPS increases iNOS expression and stimulates NO production in muscularis resident macrophages to inhibit smooth muscle contraction. LPS-induced iNOS gene expression may be mediated by autocrine regulation of PGs through the induction of COX-2 gene expression.

Membrane permeabilization induced by discodermin A, a novel marine bioactive peptide

The effects of discodermin A (DC-A), a novel marine bioactive peptide extracted from sea sponge Discodermia kiiensis, on the vascular smooth muscle cells and tissues were examined. Analysis with a confocal laser microscope showed that DC-A (0.1-30 microM) permeabilized the plasma membrane of A10 cells to the non-permeable fluorescent agents, ethidium homodimer-1 (MW = 857) and calcein (MW = 623), in a concentration-dependent manner. In the vascular tissue treated with 30 microM DC-A, addition of a micromolar concentration of Ca(2+) evoked a sustained contraction in the presence of ATP, suggesting that DC-A increased the permeability of the membrane to Ca(2+) and ATP. DC-A at higher concentrations (30 microM) significantly increased the leakage of lactate dehydrogenase (140 kD) from the vascular tissue. These results suggest that DC-A has a permeabilizing effect on the plasma membrane possibly by interacting with plasma membrane phospholipids with its six successive hydrophobic amino acid residues at N-terminal.

Species- and temperature-dependency of the decrease in myofilament Ca2+ sensitivity induced by beta-adrenergic stimulation

Although beta-adrenergic stimulation has been shown in many studies to decrease myofilament Ca2+ sensitivity in various types of cardiac muscle such as rat and rabbit ventricles, other studies disagree with this conclusion. In the present study, we aimed to explain these contradictory findings. We examined the effect of beta-adrenoceptor stimulation on Ca2+ sensitivity using guinea pig and rat ventricles. We performed the experiment at two different temperatures and compared the results. In guinea pig ventricles, isoproterenol and forskolin did not alter the relationship between [Ca2+]i and muscle force during the relaxation phase of tetanic contraction at either 24 degrees C or 30 degrees C. In rat ventricles, in contrast, isoproterenol shifted the [Ca2+]i-force curve to the right at 24 degrees C, but not at 30 degrees C. In guinea pig ventricles permeabilized by alpha-toxin, in which the cAMP/PK-A system is intact, the addition of cAMP did not decrease Ca2+ sensitivity. These results suggest that there are species- and temperature-dependent differences in the regulation of myofilament Ca2+ sensitivity by beta-adrenergic stimulation.

Regulation of shortening velocity by calponin in intact contracting smooth muscles

To elucidate the function of calponin in intact contracting smooth muscle cells in vivo, we generated mice with a mutated basic calponin (h1) locus (Yoshikawa et al., Genes Cells 3, 685-695, 1998). Crossbridge cycling rates were estimated in aortic smooth muscle by the force redevelopment following an isometric step shortening as a function of time after K(+) depolarization. Evidence is presented that calponin is involved in the inhibition of shortening velocity in the tonic phase of contraction. The phosphorylation levels of myosin regulatory light chain and cytosolic calcium concentrations were not significantly different in paired comparisons between calponin-deficient (-/-) and wild-type (+/+) muscles at any time point after stimulation. The force-velocity relationships in vas deferens smooth muscle showed that the maximum shortening velocity of -/- muscle was significantly faster than that of +/+ muscle. There was no change in the length-force relationships in both -/- and +/+ muscles of aorta and vas deferens. The results suggest that calponin plays a role in regulation of the crossbridge cycling and that it may be responsible for reduced shortening velocity during a maintained contraction of mammalian smooth muscle.

NO donor sodium nitroprusside inhibits excitation-contraction coupling in guinea pig taenia coli

In guinea pig taenia coli, the nitric oxide (NO) donor sodium nitroprusside (SNP, 1 microM) reduced the carbachol-stimulated increases in muscle force in parallel with a decrease in intracellular Ca(2+) concentration ([Ca(2+)](i)). A decrease in the myosin light chain phosphorylation was also observed that was closely correlated with the decrease in [Ca(2+)](i). With the patch-clamp technique, 10 microM SNP decreased the peak Ba(2+) current, and this effect was blocked by an inhibitor of soluble guanylate cyclase. Carbachol (10 microM) induced an inward current, and this effect was markedly inhibited by SNP. SNP markedly increased the depolarization-activated outward K(+) currents, and this current was completely blocked by 0.3 micorM iberiotoxin. SNP (1 microM) significantly increased cGMP content without changing cAMP content. Decreased Ca(2+) sensitivity by SNP of contractile elements was not prominent in the permeabilized taenia, which was consistent with the [Ca(2+)](i)-force relationship in the intact tissue. These results suggest that SNP inhibits myosin light chain phosphorylation and smooth muscle contraction stimulated by carbachol, mainly by decreasing [Ca(2+)](i), which resulted from the combination of the inhibition of voltage-dependent Ca(2+) channels, the inhibition of nonselective cation currents, and the activation of Ca(2+)-activated K(+) currents.

Ca2+-Sensitization of contraction in the h1 calponin-deficient smooth muscle

Role of h1 calponin on Ca2+-sensitivity of smooth muscle contraction was investigated using h1 calponin gene-deficient mice (CP -/-) and wild type mice (CP +/+). PGF2. induced a comparable force in intact aorta of CP +/+ and CP -/-. DPB showed similar effects to PGF2alpha. In membrane-permeabilized ileal smooth muscle, PDBu enhanced Ca2+-sensitivity of contraction comparably in CP +/+ and CP -/-. GTPgamma-S showed similar effects. Our results suggest that h1 calponin does not regulate Ca2+-sensitivity in the contractile mechanism of smooth muscle.

Muscarinic stimulation does not induce rhoA/ROCK-mediated Ca2+ sensitization of the contractile element in chicken gizzard smooth muscle

We have attempted to determine whether muscarinic stimulation induces RhoA/ROCK-mediated Ca2+ sensitization of contractions in chicken gizzard smooth muscles. rhoA is a small GTP-binding protein, and ROCK is a rhoA-associated coiled coil-forming serine/threonine kinase. The relationship between the cytosolic Ca2+ level ([Ca2+]i) and muscle force in the presence of a high K+ concentration was not different from that in the presence of carbachol. Verapamil inhibited muscle force in proportion to the decrease in [Ca2+]i in both the muscle stimulated with high K+ and that stimulated with carbachol. In addition, Y-27632 (10 microM), a ROCKs inhibitor, had no effect on the contractions. In the alpha-toxin-permeabilized muscles, Ca2+ induced a greater contraction in the presence of guanosine 5'-O-(3-thiotriphosphapte) (GTP[gamma-S]), whereas carbachol with GTP was not effective. The GTP[gamma-S]-induced Ca2+ sensitization was completely inhibited by Clostridium botulinum exoenzyme C3. Western blot analysis revealed both rhoA and ROCKII in the muscle extract. In addition, reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed the expression of both ROCKI and ROCKII mRNAs. These results suggest that Ca2+ sensitization in the chicken gizzard is elicited via a rhoA/ROCKs pathway, and that this pathway may be responsible for the augmentation of contraction by GTP[gamma-S] in the permeabilized muscles. If such a pathway does exist, however, carbachol-induced contraction may not be coupled to it, which explains the absence of Ca2+ sensitization in the intact chicken gizzard stimulated by carbachol.

Proteolysis of acidic calponin by mu-calpain

Acidic calponin is an actin binding protein expressed in smooth muscle and brain. Although the role of smooth muscle calponin (basic calponin) has been well studied, few studies have been performed on acidic calponin. In the present study, we demonstrated that acidic calponin binds to filamentous actin, but not monomeric actin. A co-sedimentation assay indicated that acidic calponin binds to actin with an apparent binding constant of 4 x 10(5) M(-1). In the presence of an excess amount of calmodulin, the binding of acidic calponin to actin was inhibited. The binding of acidic calponin to calmodulin was Ca(2+)-dependent with K(d) of 31 microM. We next investigated whether or not acidic calponin could be a substrate for mu-calpain in vitro, since it has been shown that basic calponin is cleaved by mu-calpain. The results showed that acidic calponin was also cleaved by mu-calpain. Neither the proteolytic pattern nor velocity of acidic calponin was different in the absence or presence of calmodulin. When acidic calponin had bound to actin, however, the susceptibility of the acidic calponin to mu-calpain was significantly reduced, which was reversed by the addition of calmodulin. Our results suggest that acidic calponin might be involved in the mu-calpain-regulated actin cytoskeleton.

Mechanisms of vasoinhibitory effect of cardioprotective agent, CP-060S, in rat aorta

Vasoinhibitory effects of (-)-(S)-2-[3,5-bis(1, 1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N-[2-(3, 4-methylenedioxyphenoxy)ethyl]amino]propyl]-1,3-thiazolidin- 4-one hydrogen fumarate (CP-060S), a synthesized cardioprotective agent, were examined. In the rat aortic rings, the contractile responses to cumulative application of angiotensin II, [Arg(8)]-vasopressin (vasopressin), or prostaglandin F(2alpha) were inhibited by CP-060S in a concentration-dependent manner. The Ca(2+)-induced contractions in the presence of vasopressin or prostaglandin F(2alpha) were also inhibited by CP-060S in a concentration-dependent manner. The inhibitory effect of 10(-5) M CP-060S on phenylephrine-induced contraction was as potent as that of 10(-6) M nifedipine, and the combined addition of 10(-6) M nifedipine and 10(-5) M CP-060S showed the effect similar to that of 10(-5) M CP-060S alone. In rat aorta loaded with a Ca(2+) indicator, fura-PE3, 10(-5) M CP-060S completely inhibited the high K(+)-induced increase in cytosolic Ca(2+) level ([Ca(2+)](i)) and contraction. In contrast, 10(-5) M CP-060S only partially inhibited the increase in [Ca(2+)](i) and contraction due to phenylephrine or prostaglandin F(2alpha). In the presence of 10(-6) M nifedipine, 10(-5) M CP-060S did not inhibit the increase in [Ca(2+)](i) and contraction induced by prostaglandin F(2alpha). In a Ca(2+)-free medium, the phasic increases in contraction and [Ca(2+)](i) induced by phenylephrine were not affected by 10(-5) M CP-060S. These results suggest that the vasoinhibitory effect of CP-060S in rat aortic rings is due mainly to the inhibition of L-type voltage-dependent Ca(2+)-channels.

Morphological and functional changes of rabbit mesenteric artery cultured with fetal bovine serum

The aim of this study was to examine the morphological and functional changes in rabbit mesenteric arterial tissue cultured with fetal bovine serum. In the endothelium-denuded arteries cultured under a serum-free condition for one week (serum-free arteries), morphology of the smooth muscle layer was intact. In the serum-free arteries, high K+ -induced contraction did not change but norepinephrine-induced contraction slightly decreased compared with that in the freshly isolated arteries, whereas the sensitivity to these stimulants was significantly augmented. In the medial layer of the arteries cultured with 10% fetal bovine serum for one week (serum-treated arteries), proliferation, disorientation and death of smooth muscle cells were observed. In the serum-treated arteries, both the amplitude of contractions induced by high K+ and norepinephrine and the sensitivity to these stimulants were significantly reduced compared with those of the serum-free arteries. The reduced norepinephrine-induced contraction in the serum-treated arteries was partially recovered by adding NG-monomethyl-L-arginine (L-NMMA), a nitric oxide (NO) synthase inhibitor, to the assay medium. In alpha-toxin permeabilized arteries, the amplitude of Ca2+ -induced contraction and the sensitivity of the contractile apparatus to Ca2+ were significantly reduced after serum-treatment. These results suggest that chronic serum-treatment of rabbit mesenteric arteries impairs muscle contractility by the morphological and phenotypic changes in smooth muscle cells. NO production in smooth muscle cells is also responsible for the decreased contractility after the serum-treatment.

Xestospongin C, a selective and membrane-permeable inhibitor of IP(3) receptor, attenuates the positive inotropic effect of alpha-adrenergic stimulation in guinea-pig papillary muscle

We evaluated the role of the inositol 1,4,5-triphosphate (IP(3)) receptor-mediated Ca(2+) release on the positive inotropic effects of alpha-adrenergic stimulation using a novel, potent, selective membrane-permeable blocker of IP(3) receptor, xestospongin C. Guinea-pig papillary muscle permeabilized with saponin exhibited spontaneous oscillatory contractions in solution buffered with pCa(2+) 6.5 by a low concentration of EGTA. The oscillatory activity was increased by adding 100 microM IP(3) and abolished by 1 microM ryanodine or 30 microM cyclopiazonic acid. Xestospongin C (3 microM) inhibited the IP(3)-induced increase in the oscillatory contractions without affecting basal oscillations. In intact papillary muscle, xestospongin C (3 microM) inhibited the positive inotropic effects of phenylephrine, resulting in a rightward and downward shift of the concentration-response curve for phenylephrine. On the contrary, xestospongin C did not affect the concentration-response curve for phenylephrine obtained in the presence of ryanodine (1 microM). On the other hand, xestospongin C affected neither basal contractions nor the positive inotropic effects of a high extracellular Ca(2+) concentration (3.2 mM) or that of isoprenaline (1 and 10 nM). These results suggest that the IP(3)-mediated increase in Ca(2+) release is involved in the positive inotropic effects of alpha-adrenergic stimulation in the guinea-pig cardiac muscle.

Negative inotropic effect of endothelin-1 in the mouse right ventricle

Effects of endothelin-1 on the contraction and cytosolic Ca(2+) concentrations (¿Ca(2+)(i)) of the mouse right ventricle were investigated. Endothelin-1 (1-300 nM) elicited a negative inotropic effect in a concentration-dependent manner. The endothelin-1-induced negative inotropy was antagonized by a selective endothelin ET(A) receptor antagonist, BQ-123 (cyclo ¿Asp-Pro-Val-Leu-Trp-; 3, 10 microM). Endothelin-1 reduced the peak amplitudes of both the ¿Ca(2+)(i) transient and contraction without changing inward Ca(2+) current. The relationship between peak amplitude of ¿Ca(2+)(i) and peak force generated by changing the extracellular Ca(2+) concentration (¿Ca(2+)(o)) was not affected by endothelin-1. In addition, the trajectory of the ¿Ca(2+)(i)-contraction phase plane diagram obtained at 2 mM ¿Ca(2+)(o) in the absence of endothelin-1 was superimposable on that obtained at 4 mM ¿Ca(2+)(o) in the presence of endothelin-1 (300 nM). Endothelin-1 (300 nM) translocated protein kinase C from cytosol to membrane, suggesting activation of protein kinase C. Further, a selective protein kinase C inhibitor, bisindolylmaleimide I (10 microM), inhibited the endothelin-1-induced negative inotropy. These results suggest that endothelin-1 elicits negative inotropy by reducing the amplitude of the ¿Ca(2+)(i) transient without changing inward Ca(2+) current through the activation of the endothelin ET(A) receptor followed by protein kinase C activation in the mouse right ventricle.

Resident macrophages activated by lipopolysaccharide suppress muscle tension and initiate inflammatory response in the gastrointestinal muscle layer

A great number of macrophages is found to be evenly distributed in the muscle layer of the gastrointestinal tract. We investigated their effects on smooth muscle contraction and the initiation of immune reactions such as inflammatory responses. Macrophages were demonstrated by the uptake of FITC-dextran and their ultrastructural features were elucidated by electron microscopy. Muscle layers of rats' ilea were incubated with lipopolysaccharide (LPS) for 4-8 h and the force of smooth muscle contraction was measured. The induction effect of inducible nitric oxide synthase (iNOS) on macrophages was then checked by immunohistochemistry. The expression of major histocompatibility complex (MHC) class II was also examined. Macrophages in the muscle layer were confirmed as resident macrophages and were different from a population of dendritic cells. After incubation with LPS, macrophages began to express iNOS and produced NO, and it reduced smooth muscle contraction. iNOS-immunopositive cells increased in a time-dependent manner. Macrophages also began to express MHC class II. The total number of macrophages did not alter after incubation. Results indicate that resident macrophages in the muscle layer induced iNOS as an inflammatory reaction, affected smooth muscle contraction, and initiated immune response in the smooth muscle layer of the gastrointestinal tract, when activated by LPS.

Stable transfectants of smooth muscle cell line lacking the expression of myosin light chain kinase and their characterization with respect to the actomyosin system

We constructed a plasmid vector having a 1.4-kilobase pair insert of myosin light chain kinase (MLCK) cDNA in an antisense direction to express antisense mRNA. The construct was then transfected to SM3, a cell line from vascular smooth muscle cells, producing a few stable transfectants. The down-regulation of MLCK expression in the transfectants was confirmed by both Northern and Western blots. The control SM3 showed chemotaxic motility to platelet-derived growth factor-BB, which was supported by lamellipodia. However, the transfectants showed neither chemotaxic motility nor developed lamellipodia, indicating the essential role of MLCK in the motility. The specificity for the targeting was assessed by a few tests including the rescue experiment. Despite this importance of MLCK, platelet-derived growth factor-BB failed to induce MLC20 phosphorylation in not only the transfectants but also in SM3. The mode in which MLCK was involved in the development of membrane ruffling is discussed with special reference to the novel property of MLCK that stimulates the ATPase activity of smooth muscle myosin without phosphorylating its light chain (Ye, L.-H., Kishi, H., Nakamura, A., Okagaki, T., Tanaka, T., Oiwa, K., and Kohama, K. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 6666-6671).

[Actin depolymerizing action by marine toxin, pectenotoxin-2]

Pectenotoxin-2 (PCTX-2), which is one of Diarrhetic Shellfish Poisoning (DSP), is a family of cyclic polyether macrolide toxin isolated from scallop Patinopecten yessoensis. Although PCTX-2 has a potent cytotoxic activities against several cancer cell lines, the biochemical activity of PCTX-2 has not been determined yet. To clarify the biochemical activity of PCTX-2 is the aime in this study. PCTX-2 inhibited the contractions elicited by 72.7 mM KCl or 1 microM phenyrephrine in a concentration dependent manner in the isolated rat aorta. In A10 cells, actin stressfiber in center but not in periphery of the cell was disrupted by PCTX-2 without any visible shape change. By monitoring fluorescent intensity of pyrenyl-actin, PCTX-2 was found to inhibit the velocity and the degree of actin polymerization in a concentration dependent manner. In addition, PCTX-2 decreased viscosity of F-actin measured with falling ball viscometry. Stoichiometric analysis indicated that PCTX-2 forms 1:4 complex with G-actin. These results suggest that PCTX-2 is a potent natural actin depolymerizing compound with unique mode of action.

Tight coupling between the rate of rise of Ca2+ transient and peak twitch contraction in guinea-pig papillary muscle

We evaluated the relationship between cytoplasmic Ca2+ concentration ([Ca2+]i) and force in guinea-pig papillary muscles loaded with a fluorescent Ca2+ indicator, fura-PE3. In the absence of ryanodine, [Ca2+]i transient and force were altered by changing extracellular Ca2+ concentration and stimulation frequency, and also by adding methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyri dine-5-carboxylate (Bay K 8644) or ouabain. Under these conditions, the peak force correlated linearly with the maximal rate of rise of [Ca2+]i (gamma = 0.948) more than the peak [Ca2+]i transient (gamma = 0.737). Ryanodine inhibited the increase in the maximal rate of rise of [Ca2+]i resulting in abolishment of the correlation between force and the maximal rate of rise of [Ca2+]i. These results suggest that the maximal rate of rise of [Ca2+]i reflects Ca2+ release from the sarcoplasmic reticulum, and this fraction of [Ca2+]i is crucial for determining the amplitude of twitch contractions when the sarcoplasmic reticulum is intact in guinea-pig papillary muscle.

Impairment of EDR by a long-term PDGF treatment in organ-cultured rabbit mesenteric artery

Platelet-derived growth factor (PDGF) has been shown to act chronically on blood vessels to regulate not only proliferation but also vascular tone. These effects may be at least partly due to the chronic effect of PDGF on vascular endothelium. To evaluate this possibility, we examined the effects of PDGF on the endothelium-dependent relaxation (EDR) and total RNA for endothelial nitric oxide (NO) synthase (eNOS) using an organ culture system. In rabbit mesenteric arteries cultured in a serum-free medium for 1 wk, amplitude of the substance P-induced EDR did not change, whereas dependency of the EDR on NO (approximately 60.0% vs. 18.9%) and the total amounts of recoverable eNOS mRNA estimated by RT-PCR were increased compared with those in freshly isolated arteries. Culture with PDGF for 1 wk decreased the relaxant effect of substance P and ionomycin (P < 0.01 compared with the arteries without PDGF), NO production estimated by bioassay (P < 0.01), and eNOS mRNA level, whereas the sodium nitroprusside-induced relaxation did not change. These results suggest that PDGF has a chronic effect on vascular endothelium to decrease eNOS mRNA and NO production and to impair NO-dependent EDR.

Augmented acetylcholine-induced, Rho-mediated Ca2+ sensitization of bronchial smooth muscle contraction in antigen-induced airway hyperresponsive rats

Treatment with acetylcholine (ACh) of a beta-escin-permeabilized intrapulmonary bronchial smooth muscle of the rat induced force when the Ca2+ concentration was clamped at 1 microM. The ACh-induced Ca2+ sensitization of myofilaments was significantly greater in antigen-induced airway hyperresponsive rats than in control rats. The ACh-induced Ca2+ sensitization was completely blocked by treatment with Clostridium botulinum C3 exoenzyme, an inactivator of Rho family of proteins. Moreover, the protein level of RhoA in the intrapulmonary bronchi was significantly increased in the airway hyperresponsive rats. Thus, increased airway smooth muscle contractility observed in asthmatics may be related to augmented agonist-induced, Rho-mediated Ca2+ sensitization of myofilaments.

Possible involvement of K+ channel opening to the interleukin-1 beta-induced inhibition of vascular smooth muscle contraction

We have previously shown that interleukin-1 beta relaxes vascular smooth muscle by the NO-dependent and independent mechanisms (Takizawa et al.: Eur. J. Pharmacol. 330: 143-150, 1997). In this study, we investigated the mechanism of NO-independent relaxation. Treatment of the rat aorta with interleukin-1 beta for 24 hr inhibited the high-K+ induced contraction by decreasing cytosolic Ca2+ level ([Ca2+]i). The relationship between [Ca2+]i and tension in intact muscle and the pCa-tension curves in permeabilized muscle suggested that Ca2+ sensitivity of contractile element was not changed after the interleukin-1 beta-treatment. After a treatment with interleukin-1 beta for 24 hr, contractile effects of phenylephrine (1 microM-10 microM) were markedly inhibited in the presence of L-NMMA (100 microM) applied to inhibit NO synthesis. A blocker of ATP-sensitive K+ channel, glibenclamide (1 microM), partially recovered the interleukin-1 beta-induced inhibition. In contrast, a blocker of Ca(2+)-activated K+ channel, charybdotoxin (0.1 microM), was ineffective. These results suggest that membrane hyperpolarization due to activation of ATP-sensitive K+ channels may partly be responsible for the NO-independent mechanism of interleukin-1 beta-induced inhibition of vascular smooth muscle contraction.

Effects of endothelin ET(B) receptor agonists and antagonists on the biphasic response in the ileum

In the guinea-pig ileum, both sarafotoxin S6c and IRL1620 (Suc-[Glu9,Ala11,15]endothelin-1-(8-21) induced a concentration-dependent biphasic effect (relaxation and contraction), but distinct tachyphylaxis of the tissue. Cross-tachyphylaxis and additivity experiments evidenced distinct receptors for these agonists. BQ-123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu]), an endothelin ET(A) receptor antagonist, did not affect the response induced by either agonist. PD145065 [Ac-(D-Bhg-Leu-Asp-Ile-Ile-Trp) (D-Bhg = 5H-dibenzyl[a,d]cycloheptene-10,11-dihydroglycine)], an endothelin ET(A)/ET(B) receptor antagonist, inhibited the contractions induced by IRL1620 and sarafotoxin S6c in competitive and noncompetitive manner, respectively. RES-701-1 [cyclic(Gly1-Asp9)(Gly-Asn-Trp-His-Gly-Thr-Ala-Pro-Asp-Trp-P he-Phe-Asn-Tyr-Tyr-Trp)], an endothelin ET(B1) receptor antagonist, inhibited both components of the response induced by IRL1620, whereas it inhibited mainly the relaxation induced by low sarafotoxin S6c doses. Apamin and suramin had different effects towards the agonists. Our results suggest that two endothelin ET(B) receptors with distinct signal transduction mechanism mediate the biphasic response: (1) the endothelin ET(B1) receptor: sensitive to RES-701-1 and PD145065 and (2) the endothelin ET(B2) receptor: less sensitive to RES-701-1 and PD145065.

Impairment of endothelium-dependent relaxation in the arteries cultured with fetal bovine serum

Effects of chronic treatment with fetal bovine serum on the function of vascular endothelium were examined using an organ culture system. In the rabbit mesenteric arteries cultured with 10% fetal bovine serum for 7 days, the substance P- or ionomycin-induced endothelium-dependent relaxation was significantly attenuated compared to the arteries cultured in the serum-free condition. The effects of the serum were concentration- and time-dependent. By the treatment with the serum, the amounts of nitric oxide (NO) production and total mRNA for endothelial NO synthase were reduced, whereas the sodium nitroprusside-induced relaxation was rather augmented. These results suggest that chronic treatment of rabbit mesenteric artery with fetal bovine serum decreases endothelial NO synthase mRNA, reduces NO production and impairs endothelium-dependent relaxation.

Agonist-dependent difference in the relationship between cytosolic Ca2+ level and release of vascular relaxing factors in the endothelium of rabbit aortic valve

The correlation between changes in cytosolic Ca2+ levels ([Ca2+]i) and the release of vascular relaxing factor(s) was investigated in the endothelium of rabbit aortic valve. ATP, carbachol and thapsigargin increased endothelial [Ca2+]i in rabbit aortic valve loaded with a leakage resistant, fluorescent Ca2+ indicator, fura-PE3. Release of relaxing factors was bioassayed using the 'sandwich' preparation in which contraction was measured in the endothelium-denuded rabbit aorta attached to the endothelial surface of the valve. Addition of ATP, carbachol and thapsigargin induced sustained relaxation of the phenylephrine-induced contraction of the aorta in the 'sandwich' preparation. N(G)-monomethyl-L-arginine (L-NMMA) greatly attenuated the relaxation induced by carbachol, and combined treatment with tetra-n-butylammonium completely inhibited the relaxation. These results suggest that the endothelial relaxing factors released from aortic valve are nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). When the increase in endothelial [Ca2+]i was plotted against the relaxation, the carbachol-induced increase in [Ca2+]i elicited greater relaxation than did ATP or thapsigargin at a given [Ca2+]i. This suggests that various agonists differently modulate the relationship between [Ca2+]i and release of NO.

Increased contractility of rat uterine smooth muscle at the end of pregnancy

Upon stimulation with high K+, oxytocin, prostaglandin E2, prostaglandin F2 alpha or carbachol, myometrium isolated from pregnant rats (21 days after pregnancy) developed 2-3 times greater isometric force than that from non-pregnant rats (estrus). High K+ increased the level of myosin light chain (MLC) phosphorylation to a similar extent in these tissues, and therefore pregnant myometrium developed greater contraction than non-pregnant myometrium at a given MLC phosphorylation. In the permeabilized muscle with alpha-toxin, Ca2+ (0.1-10 microM) induced greater contraction in pregnant myometrium than in non-pregnant myometrium. Ca2+ sensitivity was not altered after pregnancy. MLC kinase and phosphatase activities did not differ significantly between pregnant and non-pregnant myometria. Stimulation with 10 microM Ca2+ and 1 microM calyculin-A elicited similar magnitudes of contractions in the permeabilized muscles isolated from non-pregnant and pregnant rats. SDS-PAGE showed that the percentage of the content of MLC was not altered between these preparations, although actin content increased after pregnancy. These results suggest that the stress generating capacity of myometrium is increased after pregnancy without changing the MLC phosphorylation step. The equal capacity of force generation after the maximum phosphorylation by Ca2+ and phosphatase inhibitor suggests that a MLC phosphorylation-independent mechanism is responsible for the development of greater force in the pregnant myometrium.

[Long-term effects of growth-activating agents on smooth muscle contraction and endothelial function in organ-cultured rabbit mesenteric artery]

In the endothelium-denuded arteries cultured in the presence of FBS, morphological (i.e. smooth muscle disorientation and increase in collagen fiber) and phenotypic changes in smooth muscle were observed. Correlated with these changes, contractile force induced by high concentration of KCl and norepinephrine was significantly decreased. In addition, Ca-induced contraction in the permeabilized muscle was also significantly reduced. The reduced contractility in the FBS-treated arteries was partially recovered by the treatment with L-NMMA. In the endothelium-intact arteries cultured in the presence of FBS or PDGF, substance P and ionomycin-mediated, endothelium-dependent relaxation (EDR) was significantly decreased compared to the arteries cultured in serum-free condition. In addition, amounts of NO production and total recoverable eNOS mRNA was reduced in the FBS and PDGF-treated arteries. In these arteries, however, cGMP-dependent relaxation in smooth muscle was not impaired. These results suggest that long-term treatment of vascular tissue with growth-activating agents causes morphological or phenotypic changes nad up-regulation of NO production in smooth muscle, resulting in a reduced contractility. Furthermore, longterm treatment with these agents impairs NO-mediated EDR by decreasing eNOS mRNA and NO production.

Mechanism of relaxant effect of clonidine in isolated bovine tracheal smooth muscle

The relaxant effect of clonidine and the possible involvement of imidazoline I1 receptors in bovine tracheal smooth muscle (BTSM) were examined. Clonidine caused concentration-dependent significant relaxation in BTSM precontracted with 0.1 or 1 microM carbachol (CCh) but not in 72.7 mM KCl-induced contraction. The relaxation in CCh-contracted BTSM was inhibited by yohimbine (1 microM) and idazoxan (10 and 30 microM) but not by tetrodotoxin, indomethacin and other adrenoceptor antagonists. Oxymetazoline (0.1-100 microM) and phentolamine (0.1-100 microM) caused concentration-dependent relaxation, which was attenuated by idazoxan (10 microM). Norepinephrine (0.1-100 microM) produced concentration-dependent relaxation, which was completely abolished by propranolol (10 microM) but not by yohimbine (1 microM). In fura-PE3/AM-loaded BTSM, CCh and 72.7 mM KCl increased intracellular calcium concentration ([Ca++]i) followed by contraction. The high K+-induced increase in [Ca++]i was not affected by clonidine. In CCh-stimulated BTSM, clonidine decreased [Ca++]i and muscle force in parallel, whereas verapamil decreased [Ca++]i more strongly than muscle force. Clonidine (100 microM) inhibited the transient increase in [Ca++]i induced by CCh but not by caffeine (20 mM) in Ca++-free solution. Clonidine did not change the cAMP content in the presence of either 72.7 mM KCl or CCh. These results indicate that clonidine relaxes CCh-stimulated BTSM through the inhibition of CCh-induced increases in Ca++-influx, Ca++-release and intracellular signal transduction probably via imidazoline I1 receptors.

Distinct endothelin-B receptors mediate the effects of sarafotoxin S6c and IRL1620 in the ileum

In the guinea pig ileum, both sarafotoxin S6c (S6c) and IRL1620 induced a biphasic effect (relaxation and contraction). S6c induced strong tachyphylaxis of both components of the response, but IRL1620 induced tachyphylaxis mainly of the contractile component. Whereas the tissues rendered tachyphylactic to S6c did not respond to IRL1620, a normal biphasic response to S6c was observed in the tissues rendered tachyphylactic to IRL1620. In the presence of IRL1620, S6c could induce its biphasic effect, whereas in the presence of S6c, IRL1620 was ineffective. BQ-123, a specific ETA antagonist, did not affect the biphasic response induced by either agonist. PD145065, a potent ETA/ETB antagonist, was a competitive and a noncompetitive antagonist, respectively, of the contractile components of IRL1620 and S6c. RES-701-1, a specific ETB1 antagonist, inhibited both components of the response induced by IRL1620. However, it inhibited mainly the relaxant component induced by low doses of S6c. Apamin had different effects on endothelin-1 (ET-1), S6c, and IRL1620. Our results suggest that there are at least two distinct populations of ETB receptors mediating the biphasic response: the ETB1 receptor, sensitive to RES-701-1 and PD145065, and the ETB2 receptor, less sensitive to RES-701-1 and PD145065.

Regulatory mechanisms of calcium sensitization of contractile elements in smooth muscle

It is evident that smooth muscle contraction is regulated not only by the Ca2+/calmodulin/myosin light chain kinase system but also by modulation of Ca2+ sensitivity. Changes in free calmodulin concentrations, myosin light chain phosphorylation elicited by rho/rho-kinase, regulation of myosin phosphatase activity and thin filament-linked mechanisms are the possible mechanisms for regulation of Ca2+ sensitivity.

Effects of adrenomedullin and calcitonin gene-related peptide on contractions of the rat aorta and porcine coronary artery

1. Effects of adrenomedullin and alpha-calcitonin gene-related peptide (CGRP) on the contractions and cytosolic Ca2+ concentrations ([Ca2+]i) of the rat aorta and porcine coronary artery were investigated. Characteristics of the receptors mediating the effects of adrenomedullin and alpha-CGRP were also investigated. 2. Adrenomedullin and alpha-CGRP caused a concentration-dependent relaxation in the rat aorta contracted with noradrenaline. The IC50 values for adrenomedullin and alpha-CGRP were 2.4 nM and 4.0 nM, respectively. The relaxant effects of these peptides were abolished by removal of the endothelium and significantly attenuated by an inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine (L-NMMA, 100 microM), but not by a cyclo-oxygenase inhibitor, indomethacin (10 microM). 3. Adrenomedullin and alpha-CGRP increased the endothelial [Ca2+]i in the rat aorta with endothelium, whereas they did not change [Ca2+]i in the smooth muscle. 4. An antagonist of the CGRP1 receptor, CGRP (8-37), antagonized the relaxant effects of alpha-CGRP and the beta-isoform of CGRP (beta-CGRP) but not those of adrenomedullin in the rat aorta. 5. In the porcine coronary artery contracted with U46619, adrenomedullin and alpha-CGRP caused a concentration-dependent relaxation with an IC50 of 27.6 and 4.1 nM, respectively. Removal of the endothelium altered neither the IC50 values nor the maximal relaxations induced by adrenomedullin or alpha-CGRP. When the artery was contracted with high K+ solution (72.7 mM), these peptides caused a small relaxation. 6. Adrenomedullin and alpha-CGRP increased cyclic AMP content and decreased the smooth muscle [Ca2+]i in the porcine coronary artery. 7. CGRP (8-37) significantly antagonized the relaxant effects of adrenomedullin and alpha-CGRP in the porcine coronary artery. However, it had little effect on the relaxations induced by the beta-isoform of CGRP (beta-CGRP). 8. These results suggest that in the rat aorta, adrenomedullin and alpha-CGRP increase the endothelial [Ca2+]i, activate nitric oxide synthase and release nitric oxide, without a direct inhibitory action on smooth muscle. In the porcine coronary artery, in contrast, adrenomedullin and alpha-CGRP directly act on smooth muscle, increase cyclic AMP content, decrease the smooth muscle [Ca2+]i and inhibit contraction. The rat aortic endothelium seems to express the CGRP receptor which is sensitive to alpha-CGRP, beta-CGRP and CGRP (8-37) and the adrenomedullin specific receptor. The porcine coronary smooth muscle, in contrast, seems to express two types of CGRP receptor; one of which is sensitive to alpha-CGRP, CGRP (8-37) and adrenomedullin and the other is sensitive only to beta-CGRP.

Actin-depolymerizing effect of dimeric macrolides, bistheonellide A and swinholide A

We compared the effects of dimeric marine toxins, bistheonellide A, and swinholide A, on actin polymerization. Bistheonellide A and swinholide A possess two identical side chains with similar structures to those of other marine toxins, mycalolide B, and aplyronine A. By monitoring changes in fluorescent intensity of pyrenyl-actin, bistheonellide A was found to inhibit polymerization of G-actin and to depolymerize F-actin in a concentration-dependent manner. The relationship between the concentration of bistheonellide A and its inhibitory activity on actin polymerization suggested that one molecule of bistheonellide A binds two molecules of G-actin. We demonstrated by SDS-PAGE that the complex of G-actin with bistheonellide A, swinholide A, or mycalolide B could not interact with myosin. No evidence was found that bistheonellide A severs F-actin at the concentrations examined (molar ratio to actin; 0. 025-2.5), while swinholide A showed severing activity, although it was weaker than that of mycalolide B. We also demonstrated that the depolymerizing effect of bistheonellide A or mycalolide B is irreversible. Bistheonellide A increased, while swinholide A decreased, the rate of nucleotide exchange in G-actin, suggesting that binding of these toxins induces different conformational changes in the actin molecule. These results suggest that bistheonellide A intervenes between two actin molecules, forms a tertiary complex with each of its side chains bound to G-actin, and inhibits polymerization by sequestering G-actin from incorporation into F-actin. A difference in structure at the end of the side chain between dimeric macrolides and mycalolide B may account for the weak severing activity of the former.

Inhibition of rat platelet aggregation by mycalolide-B, a novel inhibitor of actin polymerization with a different mechanism of action from cytochalasin-D

In vitro effects of mycalolide-B (MB), isolated from marine sponge, were investigated with regard to the activation of rat platelets. Collagen-induced platelet aggregation in platelet-rich plasma (PRP) was slightly but significantly potentiated by lower concentrations of MB (0.3 and 1 microM) but was inhibited by higher concentrations (3 and 10 microM). ADP-induced platelet aggregation in PRP was also significantly prevented by MB (1-10 microM). Potentiation of ADP-induced aggregation by MB (0.3 microM) was hardly observed. G-actin contents, determined by DNase I inhibition assay, were increased in resting washed platelets incubated with MB (3 microM). In contrast, cytochalasin-D (CD) at 3 microM slightly reduced G-actin contents in resting platelets. After platelet aggregation with collagen (3 microg/ml) or ADP (10 microM), G-actin contents in platelets were reduced, indicating de novo actin polymerization. MB (3 microM) and CD (3 microM) abolished both ADP (10 microM)- and collagen (3 microg/ml)-induced platelet aggregation and actin polymerization in washed platelets. MB (1-10 microM) had no effects on intracellular Ca2+ concentrations in ADP (10 microM)-stimulated platelets. [125I]-fibrinogen binding to activated platelets with ADP (10 microM)(was inhibited by MB (0.3-3 microM) in a concentration-dependent manner. Thrombin-induced platelet-fibrin clot retraction was inhibited by MB (1 and 10 microM). These results suggest that MB inhibits platelet activation by interfering with actin polymerization through a different mechanism of action from CD. MB may be a useful tool for studying the role of actin polymerization in various cells.

Cicletanine-induced decreases in cytosolic Ca2+ level and contraction in vascular smooth muscle

The mechanism by which cicletanine (3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c]pyri dine) induces vasodilatation was examined in isolated vascular smooth muscle. Cicletanine inhibited the contraction induced by high K+, norepinephrine (NE) and prostaglandin F2alpha in a concentration-dependent manner in rat aorta. High K+ (15.8-72.7 mM) elicited elevation of cytosolic Ca2+ level ([Ca2+]i) and contraction in a concentration-dependent manner. Cicletanine (300 microM) inhibited the high K+-induced contractions without changing the [Ca2+]i/tension relationship. NE (3-300 nM) elicited greater contractions than high K+ at a given [Ca2+]i, suggesting that NE increased Ca2+ sensitivity of the contractile elements. Cicletanine inhibited the NE-induced contractions without changing the slope of the [Ca2+]i/tension relationship. Cicletanine inhibited the transient increases in both [Ca2+]i and muscle tension elicited by NE but not the transient increase in [Ca2+]i elicited by caffeine in Ca2+-free solution. Cicletanine did not inhibit contraction induced by Ca2+ in the permeabilized rabbit mesenteric artery with alpha-toxin. These results suggest that cicletanine inhibits vascular smooth muscle contraction by multiple mechanisms: 1) inhibition of Ca2+ influx via voltage-dependent Ca2+ channel and 2) inhibition of Ca2+ release mediated by the alpha-adrenoceptors, but not by caffeine.

[Effect of discodermin A, an antimicrobial peptide, on the cytoplasm membrane]

The effects of discodermin A, an antimicrobial peptide extracted from sea sponge Discodermia kiiensis, on cell membranes were investigated using vascular smooth muscle cells and erythrocytes. At lower concentrations (0.1-3 microM), discodermin A increased muscle tension with an increase in intracellular free Ca2+ concentration ([Ca2+]i) indicated by the fluorescence of Ca2+ indicator, fura-PE3, in rat aortic smooth muscle. On the other hand, the higher concentration of discodermin A (10-30 microM) accelerated the leakage of loaded fura-PE3 from cells. In rabbit mesenteric artery treaded with discodermin A, addition of micromolar concentration of Ca2+ evoked contraction in the presence of ATP, suggesting that permeability of the membrane to Ca2+ and ATP is increased by discodermin A. Confocal fluorescence microscopy showed that discodermin A permeabilized the plasma membrane of A10 cells to fluorescent agents EthD-1 and the intracellular esterase coupled with another fluorescent agent calcein. Discodermin A also showed a hemolytic effect on rabbit erythrocytes, suggesting that discodermin A permitted transmembrane passage of hemoglobin. These results suggest that discodermin A form pores of different sizes on the cytoplasm membrane in concentration- and time-dependent manners. Discodermin A may be a saponin-like bioactive peptide.

Interleukin-1beta-induced, nitric oxide-dependent and -independent inhibition of vascular smooth muscle contraction

Stimulation of vascular smooth muscle by bacterial lipopolysaccharide has been shown to produce interleukin-1beta and to induce vasodilation in septic shock. To understand the mechanisms of interleukin-1beta-induced relaxation, we examined the effects of interleukin-1beta on contractility and cyclic GMP contents of vascular smooth muscle. After treatment of the rat aorta with interleukin-1beta (20 ng/ml) for 6 h, the cyclic GMP content increased and the contraction induced by phenylephrine (1 microM) was partially inhibited. An inhibitor of nitric oxide (NO) synthase, N(G)-monomethyl-L-arginine (L-NMMA, 100 microM), prevented the inhibitory effect of interleukin-1beta. After treatment with interleukin-1beta for 24 h, the phenylephrine-induced contraction was inhibited more strongly. Neither L-NMMA (100 microM) nor aminoguanidine (100 microM) reversed the inhibition, whereas methylene blue (10 microM) partially reversed the inhibition. After treatment with interleukin-1beta for 12 or 24 h, the cyclic GMP content increased but to a level lower than that obtained with a 6-h treatment. The effects of sodium nitroprusside (1 microM) to inhibit the phenylephrine-induced contraction and to increase the cyclic GMP content were markedly suppressed by the 24-h interleukin-1beta treatment. In contrast, the 24-h interleukin-1beta treatment did not change the ability of 8-bromo-cGMP to relax the phenylephrine-stimulated aorta. Addition of L-NMMA (1 mM) during the 24 h treatment prevented NO production and preserved the sodium nitroprusside-induced cGMP generation by interleukin-1beta. The 24 h interleukin-1beta treatment increased the threshold concentration of KCl needed to induce contraction without changing the maximum contraction. In the presence of 25.4 mM KCl or the non-selective K+ channel inhibitor, tetraethylammonium, the inhibitory effect of the 24-h interleukin-1beta treatment on phenylephrine-induced contraction was restored. These results suggest that interleukin-1beta inhibits vascular smooth muscle contraction by a time-dependent, dual mechanism. After a 6-h treatment with interleukin-1beta, the NO/cyclic GMP system is activated. After a 24-h interleukin-1beta treatment, in contrast, the NO/cyclic GMP system may be desensitized and the contraction of vascular smooth muscle is inhibited by another mechanism, possibly membrane hyperpolarization.

Stellettamide-A, a novel inhibitor of calmodulin, isolated from a marine sponge

1. Stellettamide A (ST-A), a novel marine toxin isolated from a marine sponge, inhibited high K+(72.7 mM)-induced contraction in the smooth muscle of guinea-pig taenia coli with an IC50 of 88 microM. 2. In the taenia permeabilized with Triton X-100, ST-A inhibited Ca2+ (3 and 10 microM)-induced contractions with an IC50 of 46 microM for 3 microM Ca2+ and 105 microM for 10 microM Ca2+. In the permeabilized taenia, calyculin-A (300 nM), a potent inhibitor of type-1 and type-2A phosphatases, induced sustained contraction in the absence of Ca2+. ST-A had no effect on this contraction. 3. ST-A inhibited Mg2+-ATPase activity in native actomyosin prepared from chicken gizzard with an IC50 of 25 microM. 4. In a reconstituted smooth muscle contractile system containing calmodulin, myosin light chain (MLC) and MLC kinase, ST-A inhibited MLC phosphorylation with an IC50 of 152 microM. The inhibitory effect of ST-A was antagonized by increasing the concentration of calmodulin. 5. ST-A inhibited calmodulin activity, assessed by Ca2+/calmodulin-dependent enzymes, (Ca2+-Mg2+)-ATPase of erythrocyte membrane, with an IC50 of 100 microM and phosphodiesterase prepared from bovine cardiac muscle with an IC50 of 52 microM. The inhibitory effect on phosphodiesterase activity was antagonized by increasing the calmodulin concentration. 6. Interaction between ST-A and calmodulin was demonstrated by instantaneous quenching of the intrinsic tyrosine fluorescence of calmodulin by ST-A (3-300 microM). Similar results were obtained in the presence or absence of Ca2+ suggesting that ST-A binds to calmodulin and that Ca2+ is not essential for the binding of ST-A to calmodulin. 7. These results suggest that ST-A, isolated from marine metabolites, is a novel inhibitor of calmodulin.

Effect of phorbol esters on cytosolic Ca2+ level, myosin phosphorylation and muscle tension in high K(+)-stimulated bovine tracheal smooth muscle

To determine the role of protein kinase C (PKC) in bovine tracheal smooth muscle contractility, we examined the effects of phorbol esters on cytosolic Ca2+ level ([Ca2+]i), myosin light chain (MLC) phosphorylation and contractile force in intact muscle and contraction in a permeabilized preparation. In intact muscle, 12-deoxyphorbol 13-isobutyrate (DPB, 1 microM) increased the force without changing [Ca2+]i. High K+ (72.7 mM) induced sustained contraction with sustained increase in [Ca2+]i. In the muscle stimulated by high K+, 50 nM DPB increased the contractile force without changing [Ca2+]i, and 1 microM DPB increased the contractile force with decreasing [Ca2+]i. Thus DPB shifted the [Ca2+]i/force relationship for high K+ to the lower [Ca2+]i in a concentration-dependent manner. In permeabilized muscle, DPB did not induce contraction in the absence of Ca2+ (< < 0 nM), but shifted the Ca2+/force relationship to the lower Ca2+ levels. In the muscle stimulated with high K+, DPB (50 nM and 1 microM) increased MLC phosphorylation and force without changing the MLC phosphorylation/force relationship. DPB (1 microM) increased PKC activity estimated by the translocation from the cytoplasm to the membrane. These results suggest that DPB increases the Ca2+ sensitivity of MLC phosphorylation via the activation of PKC. Furthermore, DPB at higher concentration has an inhibitory effect on stimulated [Ca2+]i.

Palytoxin-induced increase in endothelial Ca2+ concentration in the rabbit aortic valve

Palytoxin (PTX) is one of the most potent toxins isolated from marine coelenterates of the genus Palythoa. It induces depolarization in various types of cells by increasing the permeability for monovalent cations. It has been reported that PTX induces endothelium-dependent relaxation of vascular smooth muscle. In this study, we examined the effect of PTX on the cytosolic Ca2+ concentration ([Ca2+]i) in the endothelium of rabbit aortic valves loaded with fluorescent Ca2+ indicators, fura-PE3 or fluo-3. PTX (10 pM-300 nM) irreversibly increased endothelial [Ca2+]i in a concentration-dependent manner. ATP and thapsigargin also increased [Ca2+]i. Imaging of [Ca2+]i with a confocal microscope revealed that PTX increased [Ca2+]i in all endothelial cells studied (n = 13). An inorganic Ca2+ entry blocker, La3+ (30 microM), had no effect on the increase in [Ca2+]i induced by PTX whereas it inhibited the sustained phase of the increase in [Ca2+]i induced by ATP or thapsigargin. The PTX-induced increase in [Ca2+]i was partially inhibited by ouabain and was abolished by removal of external Ca2+ although decrease of Na+ concentration in the incubation medium was ineffective. Activation of protein kinase C by 1 microM 12-deoxyphorbol 13-isobutyrate or inhibition of phosphatase by 10 nM calyculin-A had no effect on the increase in [Ca2+]i induced by PTX, whereas both agents inhibited the sustained phase of the increase in [Ca2+]i induced by ATP or thapsigargin. Mn2+ influx, measured by the quenching of fura-PE3 fluorescence, was accelerated by ATP or thapsigargin, but not by PTX. These results suggest that PTX increases [Ca2+]i in the endothelium of the rabbit aortic valve by increasing Ca2+ influx through a pathway which is different from that activated by ATP or thapsigargin.

Effects of chronic oral administration of a high dose of nicorandil on in vitro contractility of rat arterial smooth muscle

Nicorandil, which is structurally a nitrate and also a nicotinamide, has a vasodilator action by stimulating cyclase and ATP-sensitive K+ channel. The aim of present study was to examine the effects of chronic oral administration of a high dose of nicorandil on in vitro vascular reactivity. Nicorandil (30 mg/kg), at a dose 6-10-times higher than to decrease blood pressure in rat, was orally administered 2-times daily for a 2-4 weeks to the rats. At the end of the administration period, thoracic aorta was isolated for in vitro study. Treatment with nicorandil for 4 weeks markedly reduced the relaxant effect of nicorandil itself and other vasodilators including sodium nitroprusside, nitric oxide, endothelium-derived relaxing factor released by carbachol, 8-Br-cyclic guanosine 3',5'-monophosphate (cGMP), a K+ channel opener, levcromakalim, and forskolin. Increase in cGMP content induced by nicorandil and sodium nitroprusside was less in the aorta from nicorandil-treated rat than in the vehicle-control rat. Chronic administration of nicorandil altered neither the contractile responses to norepinephrine nor the vasodilator effect of verapamil. On the other hand, a 4-week treatment with a dose of nicorandil (2 mg/kg) sufficient to decrease blood pressure in rat showed no change in aortic response. These results suggest that in vivo chronic treatment with a high dose of nicorandil inactivates not only the guanylate cyclase activity but also the mechanism mediated by cGMP; it also attenuates the sensitivity of K+ channels to levcromakalim. Prolonged activation of the specific site may desensitize its site of action.

Increased inhibitory effect of phorbol ester on cytosolic Ca2+ level and contraction in rat myometrium after gestation

Activation of voltage-dependent Ca2+ channels by high K+ (40 mM) increased the cytosolic Ca2+ level ([Ca2+]i) (estimated by fura-PE3 fluorescence ratio) and force in myometrium isolated from pregnant (21 days after gestation) and non-pregnant (estrus) rats. 12-Deoxyphorbol 13-isobutyrate (DPB, 1 mM) decreased the high (K+)-stimulated [Ca2+]i and force in a concentration-dependent manner. The inhibitory effect was stronger in the pregnant myometrium than in the non-pregnant myometrium. In the pregnant myometrium, the increase in Ca2+ permeability by ionomycin (1 microM) greatly increased [Ca2+]i and force, which were only partially inhibited by verapamil (10 microM). DPB (1 microM) inhibited the verapamil-insensitive component of the increases in [Ca2+]i and muscle tension. Oxytocin (100 nM) and thapsigargin (1 microM) also induced a verapamil-insensitive increase in [Ca2+]i and force, and DPB (1 microM) inhibited these increments. Ca2+ sensitivity of contractile elements, estimated from the relationships between Ca2+ and muscle force in intact and alpha-toxin permeabilized muscle, was not significantly changed by DPB (1 microM). In summary, DPB inhibits the increase in [Ca2+]i more strongly in myometrium isolated from pregnant rats than that from non-pregnant rats without any change in the [Ca2+]i/tension relationship. Since DPB decreased [Ca2+]i-rise induced by three different mechanisms, DPB may activate Ca2+ extrusion, rather than to inhibit a specific influx pathway, to decrease [Ca2+]i.

Novel actin depolymerizing macrolide aplyronine A

Aplyronine A is a macrolide isolated from Aplysia kurodai. By monitoring fluorescent intensity of pyrenyl-actin, it was found that aplyronine A inhibited both the velocity and the degree of actin polymerization. Aplyronine A also quickly depolymerized F-actin. The kinetics of depolymerization suggest that aplyronine A severs F-actin. The relationship between the concentration of total actin and F-actin at different concentrations of aplyronine A suggests that aplyronine A forms a 1:1 complex with G-actin. From these results, it is concluded that aplyronine A inhibits actin polymerization and depolymerizes F-actin by nibbling. Comparison of the chemical structure of aplyronine A and another actin-depolymerizing macrolide, mycalolide B, suggests that the side-chain but not the macrolide ring of aplyronine A may account for its actin binding and severing activity.