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The Store-operated Calcium Entry Pathways in Human Carcinoma A431 Cells
Functional Properties and Activation Mechanisms
2 Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390
Address correspondence to Dr. Ilya Bezprozvanny, Department of Physiology, K4.112, UT Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75390-9040. Fax: (214) 648-2974; E-mail: Ilya.Bezprozvanny{at}UTSouthwestern.edu
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 ICRAC and moderately Ca2+–selective ISOC, support store-operated Ca2+ entry process. In previous patch-clamp experiments with a human carcinoma A431 cell line we described store-operated Imin/ICRACL 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) ICRAC and ISOC are present in A431 cells; (b) ICRAC currents are highly selective for divalent cations and fully activate within 150 s after initiation of Ca2+ store depletion; (c) ISOC currents are moderately selective for divalent cations (PBa/PCs = 14.5) and require at least 300 s for full activation; (d) ICRAC and ISOC currents are activated by PLC-coupled receptor agonists; (e) ISOC currents are supported by Imin/ICRACL channels that display 8.5–10 pS conductance for sodium; (f) ICRAC single channel conductance for sodium is estimated at 0.9 pS by the noise analysis; (g) Imin/ICRACL channels are activated in excised patches by an amino-terminal fragment of InsP3R1 (InsP3R1N); and (h) InsP3 binding to InsP3R1N is necessary for activation of Imin/ICRACL channels. Our findings provide novel information about store-operated Ca2+ influx pathways in A431 cells.
Key Words: calcium signaling • patch-clamp • inositol 1,4,5-trisphosphate • calcium channels • whole-cell
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