Miyakawa T, Kojima M, Ui M
The Ui Laboratory, Institute of Physical and Chemical Research, Hirosawa 2-1, Wako-shi 351-01, Japan.
Biochem J. 1998 Jan 1;329 ( Pt 1)(Pt 1):107-14. doi: 10.1042/bj3290107.
Ca2+ influx into cells in response to stimulation of various receptors was studied with Swiss 3T3 fibroblasts. The mechanisms involved were found to be so diverse that they were classified into four groups, Type I to IV. Type-I influx occurred, via pertussis toxin-susceptible G-proteins, immediately after internal Ca2+ mobilization by bradykinin, thrombin, endothelin, vasopressin or angiotensin II. Type-II influx induced by bombesin differed from Type I in its insusceptibility to pertussis toxin treatment. Ca2+ influx induced by prostaglandin E1, referred to as Type-III influx, was unique in that phospholipase C was apparently not activated without extracellular Ca2+, strongly suggesting that the Ca2+ influx preceded and was responsible for InsP3 generation and internal Ca2+ mobilization. More Ca2+ entered the cells more slowly via the Type-IV route opened by platelet-derived and other growth factors. These types of Ca2+ influx could be differentiated by their different susceptibilities to protein kinase C maximally activated by 1 h of exposure of cells to PMA, which inhibited phospholipase Cbeta coupled to receptors involved in Type-I and -II influx but did not inhibit growth-factor-receptor-coupled phospholipase Cgamma. Type-I and -II Ca2+ influxes, together with store-operated influx induced by thapsigargin, were not directly inhibited by exposure of cells to PMA, but Type-III and -IV influxes were completely inhibited. In addition, stimulation of receptors involved in Type-I and -IV Ca2+ influx, but not Type-II and -III influx, led to phospholipase A2 activation in the presence of extracellular Ca2+. Inhibition of Type-I and -IV Ca2+ influxes by their respective inhibitors, diltiazem and nifedipine, resulted in abolition of phospholipase A2 activation induced by the respective receptor agonists, in agreement with the notion that Ca2+ influx via these routes is responsible for receptor-mediated phospholipase A2 activation.
利用瑞士3T3成纤维细胞研究了细胞因各种受体受刺激而发生的Ca2+内流。发现其中涉及的机制非常多样，因此被分为四组，即I型至IV型。I型内流通过对百日咳毒素敏感的G蛋白，在缓激肽、凝血酶、内皮素、血管加压素或血管紧张素II动员细胞内Ca2+后立即发生。蛙皮素诱导的II型内流与I型的不同之处在于，它对百日咳毒素处理不敏感。前列腺素E1诱导的Ca2+内流（称为III型内流）很独特，因为在没有细胞外Ca2+的情况下，磷脂酶C显然不会被激活，这强烈表明Ca2+内流先于肌醇三磷酸（InsP3）的生成并对其负责，以及细胞内Ca2+的动员。更多的Ca2+通过血小板衍生生长因子和其他生长因子打开的IV型途径更缓慢地进入细胞。这些类型的Ca2+内流可以通过它们对蛋白激酶C的不同敏感性来区分，细胞暴露于佛波酯（PMA）1小时可使蛋白激酶C最大程度地激活，这抑制了与I型和II型内流相关受体偶联的磷脂酶Cβ，但不抑制生长因子受体偶联的磷脂酶Cγ。I型和II型Ca2+内流，以及毒胡萝卜素诱导的钙库操纵性内流，不会因细胞暴露于PMA而直接受到抑制，但III型和IV型内流则被完全抑制。此外，刺激参与I型和IV型Ca2+内流的受体（而不是II型和III型内流的受体），在存在细胞外Ca2+的情况下会导致磷脂酶A2激活。用各自的抑制剂地尔硫䓬和硝苯地平抑制I型和IV型Ca2+内流，导致各自受体激动剂诱导的磷脂酶A2激活被消除，这与通过这些途径的Ca2+内流负责受体介导的磷脂酶A2激活的观点一致。
