The slowly activating potassium current, termed I(Ks) , was measured in guinea pig ventricular myocytes with the whole-cell patch clamp configuration. With low concentrations of Ca2+ buffer (0.1 mM EGTA or BAPTA) in the recording pipette, a temperature increase from 21 to 31 °C dramatically accelerated activation of I(Ks). Isoproterenol increased I(Ks) under such conditions 2- to 3-fold at both temperatures. With high internal Ca buffer concentrations (EGTA or BAPTA ≥ 10 mM), I(Ks) was regulated by isoproterenol at 31 °C but not at 21 °C. We conclude that β-receptor regulation of I(Ks) is temperature and [Ca2+](i) dependent. A mechanism consistent with the results is that Ca2+ and temperature increase the availability of subunits for channel formation and regulation by the β- adrenergic pathway.
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