Outward currents in normal and hypertrophied feline ventricular myocytes

The properties of the inward rectifier K current (IK1) and the delayed rectifier K current (IK) were studied in single feline myocytes isolated from the right ventricle of normal cats and cats with experimentally induced right ventricular hypertrophy (RVH). IK1 demonstrated time-dependent decay during hyperpolarizations and showed inward rectification with a prominent negative-slope region between -30 and -10 mV. Both IK1 and IK was carried primarily by K ions. The activation of IK during depolarizations followed a monoexponential time course, whereas the deactivation of IK tail currents was either mono- or biexponential depending on the repolarization potential. IK showed marked rectification at positive potentials. A comparison of these currents in normal and hypertrophy myocytes revealed that in RVH the magnitude of IK1 is increased, whereas the magnitude of IK is decreased. IK showed steeper rectification, had slower activation, and had more rapid deactivation in RVH. These abnormalities of the IK may contribute to the prolongation of action potential duration, which characterizes pressure-overload cardiac hypertrophy.