Inwardly rectifying whole-cell and single-channel K currents in the murine macrophage cell line J774.1

Inward currents in the murine macrophage-like cell line J774.1 were studied using the whole-cell and cell-attached variations of the patch-clamp technique. When cells were bathed in Na Hanks' (KCl = 4.5 mM, NaCl = 145 mM), and the electrode contained Na-free K Hanks' (KCl = 145 mM) single-channel currents were observed at potentials below -40 mV which showed inward rectification, were K-selective, and were blocked by 2.5 mM Ba in the pipette. Single-channel conductance was 29 pS, and was proportional to the square root of [K]o. Channels manifested complex kinetics, with multiple open and closed states. The steady-state open probability of the channel was voltage dependent, and declined from 0.9 to 0.45 between -40 and -140 mV. When hyperpolarizing voltage pulses were repetitively applied in the cell-attached patch mode, averaged single-channel currents showed inactivation. Inactivation of inwardly rectifying whole-cell current was measured in Na Hanks' and in two types of Na-free Hanks': one with a normal K concentration (4.5 mM) and the other containing 145 mM K. Inactivation was shown to have Na-dependent and Na-independent components. Properties of single-channel current were found to be sufficient to account for the behavior of the macroscopic current, except that single-channel current showed a greater degree of Na-independent inactivation than whole-cell current.