Giovannucci David R, Bruce Jason I E, Straub Stephen V, Arreola Jorge, Sneyd James, Shuttleworth Trevor J, Yule David I
Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, 601 Elmwood Avenue, Rochester, NY 14642, USA.
J Physiol. 2002 Apr 15;540(Pt 2):469-84. doi: 10.1113/jphysiol.2001.013453.
The dynamics of Ca(2+) release and Ca(2+)-activated Cl(-) currents in two related, but functionally distinct exocrine cells, were studied to gain insight into how the molecular specialization of Ca(2+) signalling machinery are utilized to produce different physiological endpoints: in this case, fluid or exocytotic secretion. Digital imaging and patch-clamp methods were used to monitor the temporal and spatial properties of changes in cytosolic Ca(2+) concentration (Ca(2+)) and Cl(-) currents following the controlled photolytic release of caged-InsP(3) or caged-Ca(2+). In parotid and pancreatic acinar cells, changes in Ca(2+) and activation of a Ca(2+)-activated Cl(-) current occurred with close temporal coincidence. In parotid, a rapid global Ca(2+) signal was invariably induced, even with low-level photolytic release of threshold amounts of InsP(3). In pancreas, threshold stimulation generated an apically delimited Ca(2+) signal, while a stronger stimulus induced a global Ca(2+) signal which exhibited characteristics of a propagating wave. InsP(3) was more effective in parotid, where Ca(2+) signals initiated with shorter latency and exhibited a faster time-to-peak than in pancreas. The increased potency of InsP(3) in parotid probably results from a four-fold higher number of InsP(3) receptors as measured by radiolabelled InsP(3) binding and western blot analysis. The Ca(2+) sensitivity of the Cl(-) channels in parotid and pancreas was determined from the [Ca(2+)]-current relationship measured during a dynamic 'Ca(2+) ramp' produced by the continuous, low-level photolysis of caged-Ca(2+). In addition to a greater number of InsP(3) receptors, the Cl(-) current density of parotid acinar cells was more than four-fold greater than that of pancreatic cells. Whereas activation of the current was tightly coupled to increases in Ca(2+) in both cell types, local Ca(2+) clearance was found to contribute substantially to the deactivation of the current in parotid. These data reveal specializations of common modules of Ca(2+)-release machinery and subsequent effector activation that are specifically suited to the distinct functional roles of these two related cell types.
研究了两种相关但功能不同的外分泌细胞中Ca(2+)释放和Ca(2+)激活的Cl(-)电流的动力学，以深入了解Ca(2+)信号传导机制的分子特化是如何被用于产生不同的生理终点的：在这种情况下，即液体分泌或胞吐分泌。使用数字成像和膜片钳方法来监测在笼锁肌醇三磷酸（caged-InsP(3)）或笼锁钙（caged-Ca(2+)）的可控光解后，胞质Ca(2+)浓度（[Ca(2+)]c）变化和Cl(-)电流的时间和空间特性。在腮腺和胰腺腺泡细胞中，[Ca(2+)]c的变化和Ca(2+)激活的Cl(-)电流的激活在时间上紧密重合。在腮腺中，即使是低水平光解阈值量的InsP(3)，也总是会诱导出快速的全局Ca(2+)信号。在胰腺中，阈值刺激产生顶端限定的[Ca(2+)]c信号，而更强的刺激诱导出表现出传播波特征的全局[Ca(2+)]c信号。InsP(3)在腮腺中更有效，在腮腺中[Ca(2+)]c信号起始潜伏期更短，达到峰值的时间比胰腺更快。通过放射性标记的InsP(3)结合和蛋白质免疫印迹分析测量，腮腺中InsP(3)受体数量高出四倍，这可能导致了InsP(3)在腮腺中的效力增加。通过在笼锁钙的连续低水平光解产生的动态“Ca(2+)斜坡”过程中测量的[Ca(2+)]-电流关系，确定了腮腺和胰腺中Cl(-)通道的Ca(2+)敏感性。除了InsP(3)受体数量更多外，腮腺腺泡细胞的Cl(-)电流密度比胰腺细胞高出四倍多。虽然在两种细胞类型中电流的激活都与Ca(2+)的增加紧密耦合，但发现局部Ca(2+)清除对腮腺中电流的失活有很大贡献。这些数据揭示了Ca(2+)释放机制和随后效应器激活的共同模块的特化，这些特化特别适合这两种相关细胞类型的不同功能作用。
