Mechanisms of cytosolic Ca^<2+> oscillations following muscarinic receptor activation in single smooth muscle cells

本研究旨在阐明豚鼠回肠单个平滑肌细胞M受体激活后胞浆钙离子浓度([Ca^&lt；2+&gt；]i)振荡的可能机制，以期对[Ca^&lt；2+&gt；]i振荡的功能作用提供一定的认识。使用钙敏感染料直接测量[Ca^&lt；2+&gt；]i的变化，或通过膜片钳技术记录依赖于[Ca^&lt；2+&gt；]i的离子电流来间接测量[Ca^&lt；2+&gt；]i的变化。1.毒鼠强激动剂诱导的[Ca^&lt；2+&gt；]i振荡是由内部钙离子库周期性释放钙引起的。同样的机制也可以在G蛋白被GTP-Gamma S激活后诱导[Ca^&lt；2+&gt；]i振荡。2.肌醇1，4，5-三磷酸(InsP3)作为释放[Ca^&lt；2+&gt；]i振荡的第二信使，随着[Ca^&lt；2+&gt；]i升高到一定程度而抑制InsP3的释放作用]我和随着时间的推移，允许InsP3采取行动。这种对InsP3作用的[Ca^&lt；2+]i依赖的抑制可能有助于在M受体激活的过程中周期性地从细胞内释放钙。4.跨质膜的钙内流在调节[Ca^&lt；2+]i振荡的频率中起关键作用，这种作用是通过一种不依赖于细胞内钙离子补充的机制来实现的。电压门控性钙离子通道和一种未知的钙离子通道都参与了[Ca^&lt；2+&gt；]i振荡的调节。5.除INS-P3诱导的[Ca^&lt；2+&gt；]i振荡外，电压门控性钙离子通道还存在钙离子释放机制，但前者对[Ca^&lt；2+&gt；]i振荡的产生贡献不大。

The present study was made to elucidate the underlying mechanism of oscillations in cytosolic calcium concentration ([Ca^<2+>]i) following activation of muscarinic receptors in single smooth muscle cells of guinea-pig ileum, in an attempt to provide some insights into functional roles of [Ca^<2+>]i oscillations. Changes in [Ca^<2+>]i were measured directly using a Ca^<2+>-sensitive dye or indirectly by recording [Ca^<2+>]i-dependent ionic currents by the patch clamp technique.1.Muscarinic agonist-induced [Ca^<2+>]i oscillations occur as a result of periodic release of Ca^<2+> from internal Ca^<2+> stores. The same mechanism can be operated to induce [Ca^<2+>]i oscillations after activation of G proteins by GTPgammaS.2.Inositol 1,4,5-trisphosphate (InsP3) functions as a Ca^<2+>-releasing second messenger for generation of muscarinic [Ca^<2+>]i oscillations.3.Ca^<2+>-releasing action of InsP3 is inhibited by a rise of [Ca^<2+>]i to a certain level, and loss of the inhibition with falling [Ca^<2+>]i and with time allows InsP3 to act. This [Ca^<2+>]i-dependent inhibition of InsP3 action may contribute to periodic Ca^<2+> release from the stores during muscarinic receptor activation.4.Ca^<2+> influx across the plasma membrane has a crutial role to play in regulation of the frequency of [Ca^<2+>]i oscillations, and the effect is brought about through a mechanism independent of Ca^<2+> store replenishment. The voltage-gated Ca^<2+> channel and an as yet unidentified channel are both involved in Ca^<2+> entry responsible for modulation of [Ca^<2+>]i oscillations.5.Ca^<2+> stores have a Ca^<2+>-induced Ca^<2+> release mechanism in addition to the Ins-P3 induced Ca^<2+> release mechanism, but the former mechanism may little contribute to the generation of muscarinic [Ca^<2+>]i oscillations.