Zavecz J H, Anderson W M
Department of Pharmacology, Louisiana State University Medical Center, Shreveport.
J Appl Physiol (1985). 1992 Jul;73(1):30-5. doi: 10.1152/jappl.1992.73.1.30.
The effects of zero extracellular Ca2+ on the contractility of rat diaphragmatic strips in vitro were studied in conjunction with various pharmacological agents known to influence the intracellular Ca2+ concentration: the Na+ ionophore, monensin, and the Na(+)-K+ pump inhibitor, ouabain, which enhance [Ca2+]i, caffeine, which induces Ca2+ release from the sarcoplasmic reticulum (SR), and ryanodine, which prevents Ca2+ retention by the SR. The effect of increasing [Ca2+]i on diaphragmatic contraction was assessed by comparing contractions induced by 120 mM K+ in the small muscle strips before and after the addition of ouabain or monensin. Monensin (20 microM) and ouabain (1-100 microM) augmented contractions up to threefold. Treatment of diaphragm strips with 3 nM ryanodine increased baseline tension 360% above the original resting tension but only if the diaphragm was electrically stimulated concurrently; 100 microM ryanodine induced contracture in quiescent tissue. High K+ contractures were of greater magnitude in the presence of ryanodine compared with control, and relaxation time was prolonged by greater than 200%. Ca(2+)-free conditions ameliorated these actions of ryanodine. Ryanodine reduced contractions induced by 10 mM caffeine and nearly abolished them in Ca(2+)-free solution. The data demonstrate that extracellular Ca2+ is important in certain types of contractile responses of the diaphragm and suggest that the processes necessary to utilize extracellular Ca2+ are present in the diaphragm.
结合已知会影响细胞内钙离子浓度的各种药理试剂，研究了细胞外零钙离子浓度对体外大鼠膈肌条收缩性的影响：增强细胞内钙离子浓度的钠离子载体、莫能菌素以及钠钾泵抑制剂哇巴因；诱导肌浆网释放钙离子的咖啡因；以及阻止肌浆网储存钙离子的兰尼碱。通过比较添加哇巴因或莫能菌素前后，120 mM钾离子在小肌条中诱导的收缩，评估细胞内钙离子浓度升高对膈肌收缩的影响。莫能菌素（20 microM）和哇巴因（1 - 100 microM）可使收缩增强达三倍。用3 nM兰尼碱处理膈肌条，仅在同时进行电刺激时，基线张力比原始静息张力增加360%；100 microM兰尼碱在静止组织中诱导挛缩。与对照组相比，在存在兰尼碱的情况下，高钾挛缩幅度更大，松弛时间延长超过200%。无钙条件可改善兰尼碱的这些作用。兰尼碱可降低10 mM咖啡因诱导的收缩，在无钙溶液中几乎完全消除收缩。数据表明，细胞外钙离子在膈肌的某些类型收缩反应中很重要，并提示膈肌中存在利用细胞外钙离子的必要过程。
