CA2-ACTIVATED K+ CHANNELS REGULATE ACTION-POTENTIAL REPOLARIZATION INURINARY-BLADDER SMOOTH-MUSCLE()

The goal of this study was to examine the role of large conductance Ca 2+-activated K+ channels in the regulation of cell excitability Fn uri nary bladder smooth muscle from the guinea pig. Ca2+-activated K+ chan nels were studied with single-channel recording techniques and found t o be intracellular Ca2+ and voltage dependent and sensitive to externa l tetraethylammonium and blocked by nanomolar concentrations of iberio toxin (apparent dissociation constant of 4 nM). Spontaneous action pot entials recorded from intact tissue strips depended on external Ca2+ a nd were inhibited by Ca2+ channel blockers. Iberiotoxin (100 nM) signi ficantly altered the configuration of the action potential by increasi ng the duration and peak amplitude of the action potential and decreas ing the rate of decay. Iberiotoxin also increased the action potential frequency from 0.11 to 0.29 Hz. This study suggests that Ca2+-activat ed K+ channels play a significant role in the repolarization of the ac tion potential and in the maintenance of the resting membrane potentia l of the urinary bladder smooth muscle.