Abstract
In many cell types, the rise in cytosolic Ca(2+) due to opening of Ca(2+) release-activated Ca(2+) (CRAC) channels drives a plethora of responses, including secretion, motility, energy production, and gene expression. The amplitude and time course of the cytosolic Ca(2+) rise is shaped by the rates of Ca(2+) entry into and removal from the cytosol. However, an extended bulk Ca(2+) rise is toxic to cells. Here, we show that the plasma membrane Ca(2+) ATPase (PMCA) pump plays a major role in preventing a prolonged cytosolic Ca(2+) signal following CRAC channel activation. Ca(2+) entry through CRAC channels leads to a sustained sub-plasmalemmal Ca(2+) rise but bulk Ca(2+) is kept low by the activity of PMCA4b. Despite the low cytosolic Ca(2+), membrane permeability to Ca(2+) is still elevated and Ca(2+) continues to enter through CRAC channels. Ca(2+)-dependent NFAT activation, driven by Ca(2+) nanodomains near the open channels, is maintained despite the return of bulk Ca(2+) to near pre-stimulation levels. Our data reveal a central role for PMCA4b in determining the pattern of a functional Ca(2+) signal and in sharpening local Ca(2+) gradients near CRAC channels, whilst protecting cells from a toxic Ca(2+) overload.