Inwardly rectifying K+ current in osteoclasts

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Abstract
Membrane properties of freshly isolated rat osteoclasts were studied using the whole cell patch-clamp recording technique. The membrane potential could switch between two stable levels, approximately -70 and -15 mV. Voltage-clamp studies indicated that osteoclasts exhibited marked inward rectification, with hyperpolarizing voltage commands from -70 mV activating large inward currents. No voltage-dependent currents were observed in response to depolarization. An increase in external K+ concentration shifted the current-voltage relationship positive in a manner predicted for K+ current. Furthermore, barium and cesium reversibly suppressed the inward current. Thus the dominant current evident in osteoclasts was inwardly rectifying K+ current, resembling that found in a number of cell types, including cardiac and skeletal muscle and oocytes. The current-voltage relationship of osteoclasts was "N-shaped" and could intersect the zero-current level at three potentials, accounting for two stable membrane potentials. Switching of membrane potential between these two levels may regulate a number of the cellular processes involved in bone resorption.