Activation of potassium channels by tempol in arterial smooth muscle cells from normotensive and deoxycorticosterone acetate-salt hypertensive rats

Large-conductance Ca2+-activated potassium (BK) channels modulate vascular tone. Tempol, an O-2(-) dismutase mimetic, causes vasodilation via activation of vascular BK channels. In this study, we investigated the mechanisms underlying tempol-induced activation of BK channels in mesenteric arterial ( MA) myocytes from sham and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. In sham myocytes, whole-cell patch clamp studies showed that tempol enhanced peak outward currents (I-o). This effect was larger in DOCA-salt myocytes. Tempol caused a leftward shift in the activation curve for Io in sham and DOCA-salt myocytes. In DOCA-salt myocytes, the peak Io at +80 mV did not differ from sham myocytes, but iberiotoxin ( BK channel blocker) caused a larger reduction of Io in DOCA-salt compared with sham myocytes. Iberiotoxin but not 4-aminopyridine blocked the Io activated by tempol. Tiron, another O-2(-) scavenger, had no effect on Io. Using inside-out patches, we found that tempol caused a 4-fold increase in open probability (P-o) of BK channels but did not change the mean channel open time in sham and DOCA-salt myocytes. Tempol did not change single channel conductance in sham or DOCA-salt myocytes. Western blot and immunocytochemical studies revealed that BK channel alpha-subunit expression was increased in DOCA-salt MA compared with sham MA. The data indicate that tempol directly activates BK channels by increasing channel Po. We conclude that upregulation of the BK channel alpha-subunit protein and tempol-induced increases in BK channel Po contribute to the enhanced depressor response caused by tempol in DOCA-salt hypertensive rats.