Substance P-induced calcium entry in endothelial cells is secondary to depletion of intracellular stores.

Substance P (SP) induces an elevation in cytosolic Ca2+ concentration ([Ca2+]i) in porcine coronary artery endothelial cells by way of Ca2+ influx and release from intracellular stores. We tested the hypothesis that SP-induced Ca2+ influx occurs due to activation of a Ca(2+)-permeable influx pathway coupled to depletion of intracellular stores. With the use of the perforated patch technique and fura 2 microfluorimetry, a fivefold greater increase in [Ca2+]i per unit decrease in membrane potential was obtained in the presence of SP (10 nM) compared with resting state, implying that SP increased Ca2+ conductance. When K+ channels were blocked, SP activated a net inward current with a reversal potential (2.5 +/- 1 mV) not significantly different from that (2 +/- 1 mV) for inward current recorded in response to store depletion by (2,5-di-tert-butylhydroquinone) (BHQ, 10 microM). Increasing bath [Ca2+] induced a similar shift in reversal potential for SP- and BHQ-induced currents. Inositol 1,4,5-trisphosphate (20 microM), applied through the patch pipette, activated an inward current with Ca2+ selectivity similar to SP- and BHQ-activated currents. Dialysis of cells with heparin (5 mg/ml) completely blocked SP-induced inward current but not BHQ-induced current. These results suggest that the SP-induced increase in Ca2+ conductance can be completely explained by activation of a Ca(2+)-permeable influx pathway coupled to depletion of intracellular stores.