Effects of ketamine on voltage-dependent Ca2+ current in single smooth muscle cells from rabbit portal vein

The effects of ketamine on membrane potentials and voltage-dependent Ca2+ current were studied in dispersed single smooth muscle cells from rabbit portal vein. The resting membrane potential (-56.2 +/- 1.5mV) was not affected by ketamine (10(-5)-10(-3)M). The duration and the amplitude of the action potential evoked by intracellular stimulation were significantly decreased by ketamine in the concentrations of 10(-4)M and 10(-3)M. Voltage-gated Ca2+ current in single smooth muscle cells was apparently decreased by ketamine at concentrations of between 10(-5)M to 10(-3)M. The activation threshold of Ca2+ current (approx. -30mV) was also decreased by ketamine. Therefore, these results suggest that inhibition of the contractile response by ketamine in vascular smooth muscle from rabbit portal vein may be attributable to the inhibition of the Ca2+ current.     

Effects of protamine on vascular smooth muscle of rabbit mesenteric artery

Systemic hypotension is commonly observed in association with protamine administration after cardiopulmonary bypass. However, little information is available concerning the action of protamine on vascular smooth muscle. Thus, we investigated the action of protamine on vascular tissues using tension recording and microelectrode methods. Protamine (5-500 micrograms/ml) inhibited contractions induced by norepinephrine (NE)- or elevated K+ in a concentration-dependent manner in both endothelium-intact and -denuded strips. Protamine inhibition of NE contractions was less profound after endothelial denudation, whereas protamine inhibition of K(+)-induced contractions was less affected by prior denudation. In endothelium-intact strips, the protamine-induced inhibition was significantly reduced by inhibitors of the endothelium-derived relaxing factor pathway, including oxyhemoglobin, methylene blue, or NG-nitro-L-arginine, whereas the contractile inhibition was enhanced by superoxide dismutase. In endothelium-denuded strips, protamine inhibited Ca(2+)-induced contraction evoked in Ca(2+)-free solution containing 100 mM K+ and inhibited the NE-induced contraction under the following conditions: 1) in Ca(2+)-free solution; 2) after nifedipine treatment; and 3) after depletion of stored Ca2+ by A23187 or ryanodine. In membrane-permeabilized strips, protamine did not modify Ca(2+)-induced contraction. Protamine (50-500 micrograms/ml) did not modify the membrane potential of either endothelium-intact or -denuded strips. Furthermore, protamine irreversibly impaired acetylcholine-induced endothelium-dependent relaxant response, implying a toxic effect of protamine on the endothelium. We conclude that protamine exerts its inhibition on vascular smooth muscles in both an endothelium-dependent and -independent manner; i.e., the endothelium-dependent component is mediated probably by endothelium-derived relaxing factor, and direct smooth muscle effects are due to the inhibition of both Ca(2+)-influx and the NE-induced Ca2+ release from intracellular stores.     

依托咪酯对兔离体气管平滑肌收缩力的影响

目的：探讨依托咪酯对气管平滑肌收缩力的直接影响。方法：采用电刺激兔离体气管平滑肌并测量其张力。结果：接近于临床有效血浆浓度的依托咪酯即可显著抑制气管平滑肌的收缩,并呈剂量依赖性。结论：对有气管高反应的患者可安全地选用依托咪酯作为静脉全麻药,并有可能起到一定的治疗作用。     

Effects of phenol on vascular smooth muscle in rabbit mesenteric resistance arteries

Although phenol has long been used clinically as a neurolytic agent or as a preservative for injections, little information is available regarding its direct vascular action. We therefore studied the effects of phenol (0.1 μM–2mM) on isolated rabbit small mesenteric arteries, using isometric tension recording methods. All experiments were performed on endothelium-denuded strips. Phenol (≥10 μM) generated transsient contractions in a concentration-dependent manner in both normal Krebs and Ca²⁺-free solutions with EC₅₀ values (concentrations that produced 50% of the maximal response) of 39.8 μM and 99.7 μM, respectively. Depletion of intracellular Ca²⁺ stores by A23187 or ryanodine completely elimited the phenol-induced contractions. When caffeine (10 mM) and noradrenaline (NA, 10μM) were consecutively applied in Ca²⁺-free solution with an interval of 7 min (sufficient to prevent caffeine-induced inhibition of Ca²⁺ sensitivity), caffeine eliminated the contractions induced by subsequent application of NA. In similar experiments where phenol (1 mM) and NA (10 μM) were consecutively applied in Ca²⁺-free solution, phenol significantly inhibited contractions induced by subsequent application of NA. Phenol (0.1 mM, ∼EC₆₅), applied in the presence of either 128 mM K⁺ or NA (10 μM), produced transient vasoconstrictions superimposed on both high K⁺-and NA-induced contractions, but had a lesser effect on maintenance of these contractions. The vascular responses to high K⁺, NA, and caffeine after washout of phenol were not significantly different from those before application of phenol (up to 2 mM). The results suggest that phenol stimulates Ca²⁺ release from intracellular Ca²⁺ stores, which are sensitive to both caffine and NA in this resistance artery. The effect does not appear to reflect a toxic effect on vascular smooth muscle. It seems unlikely that phenol causes adverse hemodynamic changes because of the observed direct vascular action. Presented in part at the annual meeting of the American Society of Anesthesiologists, Atlanta, Georgia October 21–25, 1995     

Effects of isoflurane on K+ and Ca2+ conductance in isolated smooth muscle cells of canine cerebral arteries.

Although isoflurane is a known cerebral vasodilator, the mechanism of isoflurane-induced vasodilation is not clear. The purpose of this study was to investigate the effects of 2.6% isoflurane (1.2 mM) on macroscopic calcium and potassium channel currents in voltage-clamped canine middle cerebral artery cells. Cells were dialyzed with K(+)-glutamate solution and superfused with Tyrode's solution for measurement of potassium current (n = 20). Stepwise depolarization from a holding potential of -60 mV to beyond -30 mV elicited an outward, slowly inactivating potassium current that was reduced 50% +/- 2% and 81% +/- 3% (mean +/- SEM) in the presence of 1 mM 4-aminopyridine and 30 mM tetraethylammonium, respectively. Calcium ionophore (A23187, 10 microM) increased the potassium current by 76% +/- 3%, suggesting calcium dependency. Isoflurane reduced the amplitude of the potassium current by 35% +/- 4%. Calcium current was measured in cells dialyzed with solution containing 130 mM Cs(+)-glutamate and superfused with solution containing 10 mM BaCl2 and 135 mM tetraethylammonium to pharmacologically isolate the calcium current (n = 13). Under these conditions, progressive depolarizing steps from -60 mV elicited an inward current that was maximally activated at +20 mV and essentially eliminated by 1 microM nifedipine. This current, resembling a long-lasting (L-type) Ca2+ channel current, was reduced 40% +/- 4% by isoflurane. The results of this study suggest that isoflurane acts directly at the vascular muscle membrane to suppress transmembrane calcium and potassium currents. The decrease in calcium current would cause vasodilation; however, the concomitant decrease in potassium current may partially antagonize the depressant effect of isoflurane mediated through calcium current reduction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acetate relaxation of isolated vascular smooth muscle

The vasorelaxant effects of acetate in arginine vasopressin (AVP)-contracted rat tail artery strips were examined in order to study mechanism of action. Dose-dependent relaxation by acetate was found in the clinically important range of 4 to 16 mM. Relaxation was not due to complexing of ionized calcium, persisted after mechanical removal of the endothelium, and was not altered by pretreatment with indomethacin. Although acetate also inhibited contraction by alpha-1 and alpha-2 agonists, the relaxant effect was not altered by destruction of sympathetic nerve terminals using 6-hydroxydopamine. The degree of relaxation in this model by various anions correlated with their lyotropic properties; however, the vasorelaxant effect of acetate exceeded that which would be expected on the basis of its position in the lyotropic series. The vasorelaxant effect of acetate was shared by other short-chain fatty acids that can be conjugated with coenzyme A (CoA), such as propionate and malonate. In contrast, a much lesser or absent relaxant effect was found with nonfatty-acid precursors of acetyl CoA, such as pyruvate, lactate, and alanine. The vasorelaxant effect of acetate was abolished by pretreatment with DIDS, an inhibitor of organic anion uptake, suggesting that cellular uptake of acetate is essential to its vasorelaxant action. The results suggest that the relaxant effect of acetate in vascular smooth muscle is non-specific, is not mediated by prostaglandins, does not depend upon the presence of either endothelium or the sympathetic nervous system, and may be due to metabolism of acetate to acetyl CoA with attendant conversion of ATP to AMP.     

Effects of vasoactive intestinal polypeptide on isolated urethral and urinary bladder smooth muscle from rabbit and man

Vasoactive intestinal polypeptide concentration-dependently inhibited the contractant responses of isolated preparations of the female rabbit bladder and urethra induced by electrical field stimulation and exogenous application of acetylcholine (bladder) and noradrenaline (urethra). The inhibition of alpha-adrenoceptor and muscarinic cholinoceptor-mediated activity in the urethra and bladder amounted to 50 to 90 per cent of induced contractions. The nonadrenergic noncholinergic contraction induced by electrical field stimulation in the urethra was reduced slightly, whereas corresponding response in the bladder was more sensitive. The maximum inhibition of both the electrically induced responses and contractions induced by exogenous noradrenaline and acetylcholine was of comparable size in the urethra and the bladder. The effects of vasoactive intestinal polypeptide seemed to be exerted postjunctionally since no significant influence of the peptide was seen on the release of 3H-noradrenaline from adrenergic nerve endings in the urethra. The effects of vasoactive intestinal polypeptide in human urethral and bladder preparations were less consistent. The noradrenaline-induced contraction in urethral preparations was inhibited by 29 +/- 9 per cent (no. = 22). The effects on electrically induced contractions in the urethra, and on responses to acetylcholine and electrical field stimulation in the bladder, were small and inconsistent. It is concluded that vasoactive intestinal polypeptide may be of importance for regulation of lower urinary tract smooth muscle activity in the rabbit. It cannot be excluded that the peptide has a modulatory role in neurotransmission in human urethral muscle. However, the present results do not support the view of vasoactive intestinal polypeptide as an inhibitor of contraction in human detrusor.     

格列苯脲对丙泊酚、氯胺酮、依托咪酯及咪唑安定致兔离体气管平滑肌舒张作用的影响

目的：观察丙泊酚、氯胺酮、依托咪酯及咪唑安定对乙酰胆碱预处理的离体气管条的作用，并探讨该作用与ATP敏感性钾通道的关系。方法：采用离体气管条模型，首先观察丙泊酚、氯胺酮、依托咪酯及咪唑安定对乙酰胆碱预处理气管条肌张力的变化；然后用格列苯脲孵育，观察丙泊酚、氯胺酮、依托咪酯及咪唑安定对肌张力的影响。结果：丙泊酚、氯胺酮、依托咪酯及咪唑安定都可以舒张气管平滑肌，而用格列苯脲孵育后，可以部分阻断上述各药舒张气管平滑肌的效应（P＜0．01）。结论：丙泊酚、氯胺酮、依托咪酯及咪唑安定对离体气管平滑肌的舒张作用与ATP敏感性钾通道有关。     

异丙酚对兔离体气管平滑肌舒张作用机制的研究

目的探讨异丙酚在正常和炎症状态下对气管平滑肌收缩作用的影响及其机制。方法8只健康新西兰大白兔,每次试验用气栓法处死1只,每只兔制备8个气管平滑肌条,依据悬挂气管平滑肌条的营养液中处理因素不同,采用随机数字表法将气管平滑肌条随机分为8组即（每组8个）：a组（0μmol/L）,b组（异丙酚300μmol／L）,c组（环糊精-β10mmol／L）,d组（环糊精-β10mmol／L＋异丙酚300μmol／L）,c组（0μmol／L）,f组（异丙酚300μmol／L）,g组（环糊精-β10mmol／L）,h组（环糊精-β10mmol／L＋异丙酚300μmol／L）。e,f,g,h4组气管平滑肌条浸于浓度为50μg／L肿瘤坏死因子-α溶液里,并通以95％O2和5％CO2在4℃恒温冰箱冷藏12h以供试验。用Medlab生物采集系统记录平滑肌条不同时间点张力值变化。免疫组化法测定小窝蛋白-1表达。结果与a组（1．28±0．12、1．25±0．13、1．23±0．16、1．22±0．19）比较,b组（0．86±0．13、0．61±0．11、0．51±0．17、0．51±0．18）、c组（1．18±0．15、1．08±0．13、0．98±0．15、0．89±0．16）、d组（0．98±0．12、0．84±0．14、0．80±0．14、0．78±0．17）T1。时间点张力值降低,差异有统计学意义（P〈0．05）;与b组比较c,d两组T1-4各时间点张力值高,差异有统计学意义（P〈0．05）;与e组（0．92±0．16、0．91±0．12、0．89±0．13、0．81±0．16）比较,f组（0.41±0．12、0．22±0．14、0．13±0．14、0．12±0．14）、g组（0．80±0．15、0．78±0．13、0．75±0．15、0．72±0．17）、h组（0．79±0．12、0．70±0．12、0．68±0．16、0．68±0．19）T1-4时间点张力值降低,差异有统计学意义（P〈0．05）;与f组比较g、h两组T1-4时间点张力值高,差异有统计学意义（P〈0．05）;8xe两组小窝蛋白-1为高表达;b、f两组小窝蛋白．1为低表达;c、d、g、h4组小窝蛋白-1为阴性。结论异丙酚直接舒张气管平滑肌的机制可能与其抑制小窝蛋白-1的表达有关。     

异丙酚对兔离体气管平滑肌收缩力的影响

目的 探讨异丙酚对气管平滑肌的直接影响,为有气管高反应患者临床选择用药提供实验参考依据。方法 采用电刺激兔离体气管平滑肌的方法研究异丙酚对其的影响。结果 10^-4mol/L的异丙酚可使电刺激诱发的兔离体气管平滑肌收缩力下降21．6％,10^-2mol/L的异丙酚可使电刺激诱发的兔离体气管平同收缩力下降35．4％。结论 异丙酚有舒张兔离体气管平滑肌的作用。     

Mechanisms of direct inhibitory action of ketamine on vascular smooth muscle in mesenteric resistance arteries

BACKGROUND: Ketamine was previously suggested to relax vascular smooth muscle by reducing the intracellular Ca2+ concentration ([Ca2+]i). However, no direct evidence is available to indicate that ketamine reduces the [Ca2+]i in vascular smooth muscle of systemic resistance arteries. METHODS: Endothelium-intact or -denuded smooth muscle strips were prepared from rat small mesenteric arteries. Isometric force and [Ca2+]i were measured simultaneously in the fura-2-loaded, endothelium-denuded strips. In some experiments, only isometric force was measured in either the endothelium-intact or beta-escin-treated, endothelium-denuded strips. RESULTS: In the endothelium-intact strips, lower concentrations (< or = 30 microm) of ketamine slightly enhanced norepinephrine-induced contraction, whereas higher concentrations (> or = 100 microM) of ketamine inhibited both norepinephrine- and KCl-induced contractions. In the fura-2-loaded strips, ketamine (> or = 100 microM) inhibited the increases in both [Ca2+]i and force induced by either norepinephrine or KCl. Ketamine also inhibited the norepinephrine-induced increase in [Ca2+]i after treatment with ryanodine. In the absence of extracellular Ca2+, ketamine notably inhibited the norepinephrine-induced increase in [Ca2+]i, whereas it only minimally inhibited caffeine-induced increase in [Ca2+]i. Ketamine had little influence on the [Ca2+]i-force relation during force development to stepwise increment of extracellular Ca2+ concentration during either KCl depolarization or norepinephrine stimulation. Ketamine did not affect Ca2+-activated contractions in the beta-escin membrane-permeabilized strips. CONCLUSIONS: The action of ketamine on contractile response to norepinephrine consists of endothelium-dependent vasoconstricting and endothelium-independent vasodilating components. The direct vasorelaxation is largely a result of reduction of[Ca2+]i in vascular smooth muscle cells. The [Ca2+]i-reducing effects are caused by inhibitions of both voltage-gated Ca2+ influx and norepinephrine-induced Ca2+ release from the intracellular stores.     

Relaxation effects of adrenomedullin in isolated rabbit corpus cavernosum smooth muscle

OBJECTIVES: To clarify the pharmacological effects of adrenomedullin, a potent vasodilator and hypotensive peptide isolated from human phaeochromocytoma cells, on corpus cavernosal smooth muscle in vitro, as the intracavernosal injection of adrenomedullin induces penile erection in the anaesthetized cat. MATERIALS AND METHODS: The effects of adrenomedullin were investigated in isolated muscle strips from New Zealand rabbit corpus cavernosum smooth muscle pre-contracted with phenylephrine alone, in the presence of indomethacin (cyclooxygenase inhibitor), Nomega-nitro l-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), and K+-channel blockers. RESULTS: Adrenomedullin caused relaxation of isolated pre-contracted rabbit corpus cavernosum strips in a concentration-dependent manner. The response of corpus cavernosum was unaffected L-NAME, indomethacin and K+-channel blockers. CONCLUSION: The relaxation exerted by adrenomedullin in rabbit corporal tissue may arise from the effect of the drug on its specific receptors and/or calcitonin gene-related peptide-1 receptors. The relaxant effect of adrenomedullin might lead to novel clinical applications for erectile dysfunction.     

兔血管平滑肌细胞和聚羟基丁酯(PHB)的细胞相容性实验研究

目的：探索血管平滑肌细胞和新型可降解材料聚羟基丁酯（PHB）的细胞相容性，为组织工程血管的构建寻找理想的支架材料。方法：将组织块法体上培养与兔血管平滑肌细胞种植在PHB膜片和PHB三维微孔支架上，在相差显微镜下观察细胞的粘附和生长情况。用MTT法测定细胞粘附率和细胞增殖指数，复合培养7天后进行扫描电镜观察并用流式细胞仪（FCM）的测定细胞周期，DNA指数。结果：兔血管平滑肌细胞在PHB膜片上粘附率为77％，细胞增殖符合细胞的生长曲线，在PHB三维微孔支架上生长情况良好，并被证实为二倍体细胞。结论：兔血管平滑肌细胞和聚羟基丁酯（PHB）的细胞相容性较好，但细胞与材料间的粘附有待进一步改善。     

Effects of thiobarbiturates on smooth muscle reactivity in isolated aortas from spontaneously hypertensive rats

The direct effects of thiobarbiturates on helical strips of aortas from spontaneously hypertensive (SH) rats were compared with those from Wistar-Kyoto (WKY) rats. At 5-6 wk of age, the arterial pressure of SH and WKY rats did not differ, and the effects of thiobarbiturates on aortic strips from SH and WKY rats were similar. By contrast, at the age of 10-12 or 20-21 wk arterial pressure was higher in SH than in WKY rats, and responses to thiobarbiturates differed in aortic strips from SH and WKY rats: contractile responses were greater in WKY than in SH rats, and relaxing effects were greater in SH than in WKY rats. Responses to sodium nitroprusside did not differ in the aortas of SH and WKY rats, but the effects of nifedipine were greater in strips from SH rats than from WKY rats at the age of 10-12 wk. Ca2(+)-induced contractions of strips exposed to Ca2(+)-free media and depolarized by high K+ were inhibited by treatment with thiamylal; the inhibition was greater in SH than in WKY rats. The increase in smooth-muscle relaxation induced by thiobarbiturates in strips from SH rats may be due to increased sensitivity to the Ca2(+)-channel blocking action of thiobarbiturates.