KRAP is required for diffuse and punctate IP < sub > 3 < /sub > -mediated Ca < sup > 2+ < /sup > liberation and determines the number of functional IP < sub > 3 < /sub > R channels within clusters

Cell Calcium. 2022 Aug 19;107:102638. doi: 10.1016/j.ceca.2022.102638. Online ahead of print.ABSTRACTKRas-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...

Source: Cell Calcium - August 28, 2022 Category: Cytology Authors: Irene Vorontsova Jeffrey T Lock Ian Parker Source Type: research