Single channel kinetic analysis of the cAMP effect on I(Ks) mutants, S209F and S27D/S92D

The I(Ks) current is important in the heart’s response to sympathetic stimulation. β-adrenergic stimulation increases the amount of I(Ks) and creates a repolarization reserve that shortens the cardiac action potential duration. We have recently shown that 8-CPT-cAMP, a membrane-permeable cAMP analog, changes the channel kinetics and causes it to open more quickly and more often, as well as to higher subconductance levels, which produces an increase in the I(Ks) current. The mechanism proposed to underlie these kinetic changes is increased activation of the voltage sensors. The present study extends our previous work and shows detailed subconductance analysis of the effects of 8-CPT-cAMP on an enhanced gating mutant (S209F) and on a double pseudo-phosphorylated I(Ks) channel (S27D/S92D). 8-CPT-cAMP still produced kinetic changes in S209F + KCNE1, further enhancing gating, while S27D/S92D + KCNE1 showed no significant response to 8-CPT-cAMP, suggesting that these last two mutations fully recapitulate the effect of channel phosphorylation by cAMP.