Huang Y, Ho I H
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, NT, Hong Kong.
Chin J Physiol. 1996;39(1):1-8.
Both intracellular Ca2+ release and Ca2+ influx through plasma membrane channels contribute jointly to the elevation of cytoplasmic Ca2+ levels which regulate the contractility of vascular smooth muscle in response to vasoconstrictors. The objective of the present study was to design new protocols to experimentally separate three Ca(2+)-elevating pathways involved in the noradrenaline-induced contractile response, intracellular Ca2+ release, Ca2+ influx through the voltage-dependent (VDCCs) and the receptor-operated (ROCCs) Ca2+ channels with Ca2+ channel blockers in the isolated rat aortic rings. VDCCs were simply activated by membrane depolarization with 60 mM K+ solution and Ca2+ release from internal stores was reflected by the noradrenaline-induced contraction in Ca(2+)-free, high K4 solution. Nifedipine, diltiazem and verapamil concentration-dependently inhibited VDCCs and intracellular Ca2+ release with high affinity. ROCCs were activated by the following procedures: the noradrenaline-induced contractile response due to intracellular Ca2+ release was fully reversed by nifedipine at 100 nM, diltiazem at 3 microM and verapamil at 10 microM, the concentration of each drug was 10-fold greater than that causing a complete inhibition of VDCCs. Under this condition, addition of 1 mM Ca2+ induced a second sustained contraction which was fully reversed by 0.3 microM prazosin. The second contractile response was most likely caused by Ca2+ influx through the noradrenaline-activated ROCCs. Higher concentrations of diltiazem and verapamil were needed to inhibit ROCCs, and nifedipine was without effect. The sensitivity order of Ca2+ channel blockers for three Ca(2+)-elevating pathways was the same: VDCCs > intracellular Ca2+ release > ROCCs. The present results indicate that VDCCs can be functionally separated from ROCCs with the experimental designs used in this study and noradrenaline evoked contractions of rat aorta by activating intracellular Ca2+ release and Ca2+ influx through VDCCs and ROCCs. However, Ca2+ influx via ROCCs makes a small contribution to the noradrenaline-induced contractile response.
细胞内Ca2+释放和通过质膜通道的Ca2+内流共同导致细胞质Ca2+水平升高，这调节了血管平滑肌对血管收缩剂的收缩反应。本研究的目的是设计新的实验方案，以分离去甲肾上腺素诱导的收缩反应中涉及的三种Ca(2+)升高途径，即细胞内Ca2+释放、通过电压依赖性（VDCCs）和受体操纵性（ROCCs）Ca2+通道的Ca2+内流，使用Ca2+通道阻滞剂处理离体大鼠主动脉环。VDCCs可通过用60 mM K+溶液使膜去极化而简单激活，细胞内储存的Ca2+释放可通过去甲肾上腺素在无Ca(2+)的高K4溶液中诱导的收缩来反映。硝苯地平、地尔硫䓬和维拉帕米以浓度依赖性方式高亲和力抑制VDCCs和细胞内Ca2+释放。ROCCs通过以下步骤激活：在100 nM硝苯地平、3 microM地尔硫䓬和10 microM维拉帕米作用下，去甲肾上腺素诱导的由于细胞内Ca2+释放引起的收缩反应完全逆转，每种药物的浓度比导致VDCCs完全抑制的浓度高10倍。在此条件下，加入1 mM Ca2+诱导第二次持续收缩，该收缩被0.3 microM哌唑嗪完全逆转。第二次收缩反应很可能是由Ca2+通过去甲肾上腺素激活的ROCCs内流引起的。抑制ROCCs需要更高浓度的地尔硫䓬和维拉帕米，而硝苯地平无效。Ca2+通道阻滞剂对三种Ca(2+)升高途径的敏感性顺序相同：VDCCs>细胞内Ca2+释放>ROCCs。本研究结果表明，使用本研究中的实验设计，VDCCs可与ROCCs在功能上分离，去甲肾上腺素通过激活细胞内Ca2+释放以及通过VDCCs和ROCCs的Ca2+内流引起大鼠主动脉收缩。然而，通过ROCCs的Ca2+内流对去甲肾上腺素诱导的收缩反应贡献较小。
