The Store-operated Calcium Entry Pathways in Human Carcinoma A431 Cells: Functional Properties and Activation Mechanisms

Activation of phospholipase C (PLC)-mediated signaling pathways in nonexcitable cells causes the release of Ca(2+) from intracellular Ca(2+) stores and activation of Ca(2+) influx across the plasma membrane. Two types of Ca(2+) channels, highly Ca(2+)–selective I(CRAC) and moderately Ca(2+)–selective I(SOC), support store-operated Ca(2+) entry process. In previous patch-clamp experiments with a human carcinoma A431 cell line we described store-operated I(min)/I(CRACL) plasma membrane Ca(2+) influx channels. In the present paper we use whole-cell and single-channel recordings to further characterize store-operated Ca(2+) influx pathways in A431 cells. We discovered that (a) I(CRAC) and I(SOC) are present in A431 cells; (b) I(CRAC) currents are highly selective for divalent cations and fully activate within 150 s after initiation of Ca(2+) store depletion; (c) I(SOC) currents are moderately selective for divalent cations (P(Ba/)P(Cs) = 14.5) and require at least 300 s for full activation; (d) I(CRAC) and I(SOC) currents are activated by PLC-coupled receptor agonists; (e) I(SOC) currents are supported by I(min)/I(CRACL) channels that display 8.5–10 pS conductance for sodium; (f) I(CRAC) single channel conductance for sodium is estimated at 0.9 pS by the noise analysis; (g) I(min)/I(CRACL) channels are activated in excised patches by an amino-terminal fragment of InsP(3)R1 (InsP(3)R1N); and (h) InsP(3) binding to InsP(3)R1N is necessary for activation of I(min)/I(CRACL) channels. Our findings provide novel information about store-operated Ca(2+) influx pathways in A431 cells.