Calcium-release-activated calcium influx in endothelium

Signaling pathways activated by the tachykinin substance P (SP) were investigated in pig coronary artery endothelial cells (PCAECs). Single cells were obtained after enzymatic digestion of coronary arteries. Intracellular Ca2+ ([Ca2+]i) was measured from fura-2 fluorescence while membrane potential or ionic current was measured using patch-clamp techniques. In physiological saline solution, SP induced hyperpolarizations or outward currents which coincided with biphasic [Ca2+]i increases representing store release of Ca2+ and Ca2+ influx. Single channel recording protocols showed that both sources of Ca2+ activated a small conductance K+ channel, resulting in cell hyperpolarization. When outward currents were blocked by d-tubocurare, Cs+, or BAPTA, an inward current was unmasked. Ion substitution protocols showed that the SP-induced inward current was (1) carried by a mixture of Ca2+ and Na+, (2) blocked by La3+, and (3) inactivated by high extracellular [Ca2+]. Tyrosine kinase inhibitors also blocked the inward current. The same current was activated by bath application of BHQ, an inhibitor of the endoplasmic reticulum Ca2+ ATPase, or by cell dialysis with IP3. These results suggest that the plateau phase of the agonist-activated [Ca2+]i increase in PCAECs reflects Ca2+ entry through a depletion-activated Ca2+ channel. The characteristics of this channel are compared to those of Ca2+ channels found in other nonexcitable cells.