A FLICKERY BLOCK OF A K-SENSING RECEPTORS IN DISPERSED BOVINE PARATHYROID CELLS( CHANNEL MEDIATED BY EXTRACELLULAR CA2+ AND OTHER AGONISTS OF THE CA2+)

Single K+ channel activities in parathyroid cells were studied using t he patch-clamp technique. A K+ channel modulated by external Ca2+ (Ca( 2+)o) was identified. This channel had a unitary conductance of 109pS at 150 mM K(+)o in the pipette solution. An increase in Ca(2+)o from 0 .5-0.75 to 2-3 mM induced a flickery partial block of the channel over a wide voltage range. The mechanism of channel blockade included a si gnificant increase in the number of closings per burst and a reduction of the mean open times. Addition of other divalent and polyvalent ago nists of the Ca2+-sensing receptor (CaR) induced a similar channel blo ckade. With its typical characteristics and flickery block by CaR agon ists, this channel differs from previously described types of K+ chann els. It is probably strongly coupled to the CaR and may contribute to the depolarization of parathyroid cells which is known to occur at ele vated levels of Ca(2+)o. (C) 1997 Academic Press