已确定KRas诱导的肌动蛋白相互作用蛋白(KRAP)对于介导内质网释放Ca2的三磷酸肌醇受体(IP3R)的适当定位和功能至关重要。这里,我们在HeLa和HEK293细胞中使用了KRAP表达的siRNA敲低来研究KRAP在IP3介导的局部Ca2+泡的产生和全局,细胞范围的Ca2+信号。高分辨率Ca2成像显示,KRAP击倒可大大降低抽吸的平均振幅,而单个IP3R通道开口期间的Ca2通量受影响很小。在对照和KRAP敲低细胞中,抽吸位点基础的簇中的功能通道数量是按照泊松关系随机分布的,但是通过KRAP敲除,每个位点的功能通道的平均数量减少了约三分之二.WeconcludedthatKRAPisrequiredforactivityofIP3Rchannelsatpuffsitesandratchally\'licenses\'thefunctionofindividualchannelsonaone-to-onebasis,而不是确定整个抽吸部位的功能。除了抽吸活动(\'点状\'Ca2+释放),全球,由较高水平的IP3引起的细胞范围内的Ca2信号进一步由Ca2释放的离散“扩散”模式组成。通过应用波动分析来隔离全局Ca2信号中的点状成分,我们发现KRAP敲低在野生型细胞和仅表达1型和3型IP3Rs的HEK293细胞中抑制相似程度的点状和弥漫性Ca2+释放。因此,KRAP似乎对于参与弥漫性Ca2释放的IP3R以及产生局部Ca2泡的聚集的IP3R的功能至关重要。
KRas-induced actin-interacting protein (
KRAP) has been identified as crucial for the appropriate localization and functioning of the inositol trisphosphate receptors (IP3Rs) that mediate Ca2+ release from the endoplasmic reticulum. Here, we used siRNA knockdown of
KRAP expression in HeLa and HEK293 cells to examine the roles of
KRAP in the generation of IP3-mediated local Ca2+ puffs and global, cell-wide Ca2+ signals. High resolution Ca2+ imaging revealed that the mean amplitude of puffs was strongly reduced by KRAP knockdown, whereas the Ca2+ flux during openings of individual IP3R channels was little affected. In both control and
KRAP knockdown cells the numbers of functional channels in the clusters underlying puff sites were stochastically distributed following a Poisson relationship, but the mean number of functional channels per site was reduced by about two thirds by
KRAP knockdown. We conclude that KRAP is required for activity of IP3R channels at puff sites and stochastically \'licenses\' the function of individual channels on a one-to-one basis, rather than determining the functioning of the puff site as a whole. In addition to puff activity (\'punctate\' Ca2+ release), global, cell-wide Ca2+ signals evoked by higher levels of IP3 are further composed from a discrete \'diffuse\' mode of Ca2+ release. By applying fluctuation analysis to isolate the punctate component during global Ca2+ signals, we find that KRAP knockdown suppresses to similar extents punctate and diffuse Ca2+ release in wild-type cells and in HEK293 cells exclusively expressing type 1 and type 3 IP3Rs. Thus,
KRAP appears essential for the functioning of the IP3Rs involved in diffuse Ca2+ release as well as the clustered IP3Rs that generate local Ca2+ puffs.