Characteristics and a functional implication of Ca(2+)-activated K(+) current in mouse aortic endothelial cells

We employed the patch-clamp technique to investigate a Ca(2+)-activated K(+) (K(Ca)) current in cultured mouse aortic endothelial cells (MAECs). In the whole-cell mode, an increase in cytosolic [Ca(2+)] ([Ca(2+)](i)) to 2 micro M 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 EC(50) (740 nM) were obtained from the current/[Ca(2+)](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, Ca(2+)-activated K(+) (IK(Ca)) channel blockers charybdotoxin (50 nM), clotrimazole (10 micro M) and econazole (10 micro M) 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 IK(Ca) channel openers chlorzoxazone, zoxazolamine and 1-ethyl-2-benz-imidazolinone and the Ca(2+)-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 IK(Ca) channel blockers inhibited the ATP-induced [Ca(2+)](i) increase in MAECs and the endothelium-dependent relaxation of mouse aortic rings. In addition, the IK(Ca) channel openers augmented ATP-induced [Ca(2+)](i) increase in MAECs and evoked endothelium-dependent relaxation of mouse aorta. These results suggest that an mIK1-like channel mediates the native IK(Ca) current in MAECs and may contribute to endothelium-dependent relaxation by modulating MAEC [Ca(2+)](i).