Substance P and bradykinin activate different types of K-Ca currents to hyperpolarize cultured porcine coronary artery endothelial cells

1. Substance P and bradykinin, endothelium-dependent vasodilators of pig co ronary artery, trigger in endothelial cells a rise in cytosolic Ca2+ concen tration ([Ca2+](i)) and membrane hyperpolarization. The aim of the present study was to determine the type of Ca2+-dependent K+ (K-Ca) currents underl ying the endothelial cell hyperpolarization. 2. The substance P-induced increase in [Ca2+](i) was 30% smaller than that induced by bradykinin, although the two peptides triggered a membrane hyper polarization of the same amplitude. The two agonists evoked a large outward K+ current of the same conductance at maximal stimulation. Agonists applie d together produced the same maximal current amplitude as either one applie d alone. 3. Iberiotoxin (50 nM) reduced by about 40% the K+ current activated by bra dykinin without modifying the substance P response. Conversely, apamin (1 m u M) inhibited the substance P-induced K+ current by about 65%, without aff ecting the bradykinin response. Similar results were obtained on peptide-in duced membrane hyperpolarization. 4. Bradykinin-induced, but not substance P-induced, endothelium-dependent r elaxation resistant to N-G-nitro-L-arginine and indomethacin was partly inh ibited by 3 mu M 17-octadecynoic acid (17-ODPA), an inhibitor of cytochrome P450 epoxygenase. Similarly the bradykinin-induced K+ current was reduced by 17-ODYA. 5. Our results show that responses to substance P and bradykinin result in a hyperpolarization due to activation of different K-Ca currents. A current consistent with the activation of large conductance (BKCa) channels was ac tivated only by bradykinin, whereas a current consistent with the activatio n of small conductance (SKCa) channels was stimulated only by substance P. The observation that a similar electrical response is produced by different pools of channels implies distinct intracellular pathways leading to K-Ca current activation.