INWARDLY RECTIFYING POTASSIUM CURRENT IN RABBIT OSTEOCLASTS - A WHOLE-CELL AND SINGLE-CHANNEL STUDY

Ionic conductances of rabbit osteoclasts were investigated using both whole-cell and cell-attached configurations of the patch-clamp recordi ng technique. The predominant conductance found in these cells was an inwardly rectifying K+ conductance. Whole-cell currents showed an N-sh aped current-voltage (I-V) relation with inward current activated at p otentials negative to E(K). When external K+ was varied, I-V curves sh ifted 53 mV/10-fold change in [K+]out, as predicted for a K+-selective channel. Inward current was blocked by Ba2+ and showed a time-depende nt decline at negative potentials, which was reduced in Na+-free exter nal solution. Inward single-channel currents were recorded in the cell -attached configuration. Single-channel currents were identified as in ward-rectifier K+ channels based on the following observations: (i) Un itary I-V relations rectified, with only inward current resolved. (ii) Unitary conductance (gamma) was 31 pS when recorded in the cell-attac hed configuration with 140 mM K+ in the pipette and was found to be de pendent on [K+]. (iii) Addition of Ba2+ to the pipette solution abolis hed single-channel events. We conclude that rabbit osteoclasts possess inwardly rectifying K+ channels which give rise to the inward current recorded at negative potentials in the whole-cell configuration. This inwardly rectifying K+ current may be responsible for setting the res ting membrane potential and for dissipating electrical potential diffe rences which arise from electrogenic transport of protons across the o steoclast ruffled border.