Two types of K+ currents underlying inward rectification of rat osteoclast membrane: a single-channel analysis

1) Electrical membrane properties of spread type-osteoclasts were examined using the whole-cell and cell-attached configurations of the patch clamp technique. The membrane potential of the osteoclasts was measured and grouped into two populations: hyperpolarized and depolarized (around -80 and 0 mV, respectively). The current-voltage relation was N-shaped, showing the property of inward rectification which was produced by K+ conductance. Either Na+ or Ca2+ inward currents were not observed. 2) The single-channel recordings were made with osteoclasts of the hyperpolarized population. Two types (slow and fast) of the current were analyzed, which appeared predominantly and had large unit conductances. The reversal potential for both types shifted according to the equilibrium potential for K+. 3) The slow type had high open probabilities (> or = 0.85) at all potentials examined. The mean open time was 349 ms at the resting potential (RP) and had a tendency to become shorter with hyperpolarization of the membrane. The closed time histogram was fitted with a double exponential function, yielding closed times of 8.3 and 55.2 ms at RP, which were not changed by hyperpolarization. The unit conductance was 32.0 pS. No outward currents were recorded at depolarized potentials to RP. 4) The open probability of the fast type was 0.25 at RP and increased with hyperpolarization of the membrane (0.55 at -80 mV to RP). The mean open time was short (2.6 ms at RP), which became longer with hyperpolarization. The channel had two closed times, 2.8 and 15.3 ms at RP, which were not voltage dependent. The unit conductance was 38.8 pS in the range of hyperpolarization from RP. The amplitude of outward currents evoked by voltage pulses beyond RP was small, probably due to rapid flickering of the current. 5) The two types of single-channel K+ currents showed the inwardly rectifying property and may play an important role in the inward rectification seen in the whole-cell configuration.