2 TYPES OF K- A SINGLE-CHANNEL ANALYSIS( CURRENTS UNDERLYING INWARD RECTIFICATION OF RAT OSTEOCLAST MEMBRANE )

1) Electrical membrane properties of spread type-osteoclasts were exam ined using the whole-cell and cell-attached configurations of the patc h clamp technique. The membrane potential of the osteoclasts was measu red 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 produc ed by K+ conductance. Either Na+ or Ca2+ inward currents were not obse rved. 2) The single-channel recordings were made with osteoclasts of t he hyperpolarized population. Two types (slow and fast) of the current were analyzed, which appeared predominantly and had large unit conduc tances. The reversal potential for both types shifted according to the equilibrium potential for K+. 3) The slow type had high open probabil ities (greater than or equal to 0.85) at all potentials examined. The mean open time was 349 ms at the resting potential (RP) and had a tend ency to become shorter with hyperpolarization of the membrane. The clo sed time histogram was fitted with a double exponential function, yiel ding 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 curren ts were recorded at depolarized potentials to RP. 4) The open probabil ity of the fast type was 0.25 at RP and increased with hyperpolarizati on of the membrane (0.55 at -80 mV to RP). The mean open time was shor t (2.6 ms at RP), which became longer with hyperpolarization. The chan nel had two closed times, 2.8 and 15.3 ms at RP, which were not voltag e dependent. The unit conductance was 38.8 pS in the range of hyperpol arization from RP. The amplitude of outward currents evoked by voltage pulses beyond RP was small, probably due to rapid flickering of the c urrent. 5) The two types of single-channel K+ currents showed the inwa rdly rectifying property and may play an important role in the inward rectification seen in the whole-cell configuration.