Characteristics and a functional implication of Ca2+-activated K+ current in mouse aortic endothelial cells

We employed the patch-clamp technique to investigate a Ca2+-activated K+ (K-Ca) current in cultured mouse aortic endothelial cells (MAECs). In the whole-cell mode, an increase in cytosolic [Ca2+] ([Ca2+](i)) to 2 muM activated an outwards current. The [K+](o)-dependent change of the reversal potentials agreed well with the predicted Nernstian relation, suggesting that it was a K-Ca current. The Hill coefficient (4) and EC50 (740 nM) were obtained from the current/[Ca2+](i) relationship. Iberiotoxin (50 nM) or apamin (200 nM) failed to inhibit the current, whereas TEA (10 mM) suppressed the current to 73.6+/-1.6% of control (n=9). The intermediate-conductance, Ca2+-activated K+ (IKCa) channel blockers charybdotoxin (50 nM), clotrimazole (10 muM) and econazole (10 muM) inhibited the K-Ca current to 10.5+/-1.3% (n=6), 16.6+/-3.1% (n=6), and 19.3+/-2.5% (n=5) of control, respectively. The IKCa channel openers chlorzoxazone, zoxazolamine and 1-ethyl-2-benz-imidazolinone and the Ca2+-activated Cl- channel blocker niflumic acid activated the K-Ca current. In inside-out patches, the single-channel conductance was 17.7 pS in symmetrical K+ solutions. RT-PCR analysis showed transcripts of the murine IK1 channel (mIK1) in MAECs. The IKCa channel blockers inhibited the ATP-induced [Ca2+](i) increase in MAECs and the endothelium-dependent relaxation of mouse aortic rings. In addition, the IKCa channel openers augmented ATP-induced [Ca2+](i) increase in MAECs and evoked endothelium-dependent relaxation of mouse aorta. These results suggest that an mIK1-like channel mediates the native IKCa current in MAECs and may contribute to endothelium-dependent relaxation by modulating MAEC [Ca2+](i).