Properties of inwardly rectifying K+ channels in ventricular myocytes.

The voltage- and time-dependent properties of whole-cell, multi-channel (outside-out), and single channel inwardly-rectifying K+ currents were studied using adult and neonatal rat, and embryonic chick ventricular myocytes. Inward rectification of the current-voltage relationship was found in the whole-cell and single channel measurements. The steady-state single channel probability of opening decreased with hyperpolarization from EK, as did the mean open time, thereby explaining the time-dependent inactivation of the macroscopic current. Myocytes dialysed with a Mg++-free K+ solution (to remove the property of inward rectification) displayed a quasi-linear current-voltage relationship. The outward K+ currents flowing through the modified inward rectifier channels were able to be blocked by the local anesthetic and anti-arrhythmic agent, lidocaine.