INWARDLY RECTIFYING K+ CHANNELS IN DISPERSED BOVINE PARATHYROID CELLS

Excitation-secretion coupling in various endocrine cells is dependent on membrane voltage which is controlled by ion channels. In order to c haracterize and determine the functional significance of voltage-gated ion channels in the parathyroid cell, the patch clamp technique was u sed in cell-attached and whole cell configurations to study single cha nnel and whole cell currents in dispersed bovine parathyroid cells. Wh ole cell voltage clamp recordings from dissociated bovine parathyroid cells were obtained in a physiologic solution containing (in mM): 140 NaCl, 5.4 KCl 2 CaCl2, and 2 MgCl2. The pipette (intracellular) soluti on contained tin mM) 145 KAsp, 10(-5) CaCl2, and 2 MgCl2. Currents wer e recorded in response to 20-mV incremental changes in voltage of 300- ms duration every 3 s from -80 to +40 mV and from -40 to -140 mV. Ther e was a small outward current recorded in response to 300-ms pulses of 20-mV increments from -80 to +40 mV, A large inward current was recor ded following hyperpolarization of the parathyroid cell from -40 to -1 40 mV, The reversal potential for the current was -60 to -65 mV, sugge sting that the majority of the current is carried by a channel that is K+ selective. Our results suggest that the whole cell currents of dis persed bovine parathyroid cells in physiologic extracellular solution include an in inwardly rectifying K+ current which is open at low intr acellular calcium concentration. This inwardly rectifying K+ channel i s likely to play a major role in maintaining negative membrane potenti al by opposing calcium-induced depolarization of the parathyroid cell and, as a result, may have an important role in regulation of PTH secr etion. (C) 1998 Academic Press.