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 Ca2+ from intracellular Ca2+ stores and activation of Ca2+ influx across the plasma membrane. Two types of Ca2+ channels, highly Ca2+-selective I-CRAC and moderately Ca2+-selective I-SOC, support store-operated Ca2+ entry process. In previous patch-clamp experiments with a human carcinoma A431 cell line we described store-operated I-min/I-CRACL plasma membrane Ca2+ influx channels. In the present paper we use whole-cell and single-channel recordings to further characterize store-operated Ca2+ 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 Ca2+ store depletion; (c) I-SOC currents are moderately selective for divalent cations (PBa/PCs = 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 Ca2+ influx pathways in A431 cells.