Modulation of Substance P-Induced K+ Current in Coronary Endothelium

Substance P (SP) activates an outward K+ current, membrane hyperpolarization and increases cytosolic Ca2+ ([Ca2+],) in porcine coronary artery endothelial cells (PCAECs). We tested the importance of Ca2+, CAMP, cGMP, arachidonic acid and G protein-linked pathways in modulating whole-cell K+ currents activated by SP. Current or membrane potential and [Ca2+], were measured simultaneously in single cells in response to SP (10 nM), using the perforated patch technique and fura-2 microfluorimetry. Partial block of Kcachannels by D-tubocurarine resulted in a significant reduction in SP-induced membrane hyperpolarization and the plateau phase of the cell [Ca2+]i response. In PCAECs preloaded with BAPTA, SP failed to elevate [Ca2+]i or activate outward current. In Ca2+-free bath solution, SP induced transient elevations in [Ca2+]i and outward current. With SP still present, addition of 1 mM Ca2+ to the bath after [Ca2+]i returned to resting levels elevated [Ca2+]i and elicited outward current. Acute application o...