Plasma membrane calcium channels in human carcinoma A431 cells are functionally coupled to inositol 1,4,5-trisphosphate receptor-phosphatidylinositol 4,5-bisphosphate complexes

In most nonexcitable cells, calcium (Ca2+) release from inositol 1,4,5-trisphosphate (InsP(3))-sensitive intracellular Ca2+ stores is coupled to Ca2+ influx (calcium release-activated channels (I-CRAC)) pathway. Despite intense investigation, the molecular identity of I-CRAC and the mechanism of its activation remain poorly understood, InsP(3)-dependent miniature calcium channels (I-min) display functional properties characteristic for I-CRAC. Here we used patch clamp recordings of I-min channels in human carcinoma A431 cells to demonstrate that I-min activity was greatly enchanced in the presence of anti-phosphatidylinositol 4,5-bisphosphate antibody (PIP(2)Ab) and diminished in the presence of PIP2. Anti-PIP2 antibody induced a greater than B-fold increase in I-min,sensitivity for InsP(3) activation and an almost 4-fold change in I-min maximal open probability. The addition of exogenous PIP2 vesicles to the cytosolic surface of inside-out patches inhibited I-min activity. These results lead us to propose an existence of a Ca2+ influx pathway in nonexcitable cells activated via direct conformational coupling with a selected population of InsP(3) receptors, located just underneath the plasma membrane and coupled to PIP2. The described pathway provides for a highly compartmentalized Ca2+ influx and intracellular Ca2+ store refilling mechanism.