AN INTERMEDIATE CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNEL IN RAT VISCERAL SENSORY AFFERENT NEURONS

Whole-cell and single channel recordings were used to characterize an intermediate conductance calcium-activated potassium (KCa) channel in sensory neurons of the nodose ganglion. From a -80 mV holding potential, the total outward current in these neurons was increased when extracellular calcium was raised from 0.02 to 5 mM. This calcium-evoked outward current was not blocked by either charybdotoxin (50 nM) or apamine (40 nM). In the inside-out patch configuration, the current-voltage relationship for this channel was linear between -60 and +60 mV in symmetrical 145 mM potasssium aspartate (KAsp) and possessed a conductance of approximately 60 picosiemens (pS). Increasing [Ca2+](i) from 0.01 mu M to 1.0 mu M markedly increased the cumulative open probability of this channel and the effect of increasing [Ca2+](i) on these channels was not voltage dependent. In the outside-out patch configuration, neither tetraethylammonioum (TEA), (1 mM), apamine (40 nM) or charybdotoxin (ChTx) (50 nM) had any effect on the activity of this channel. These results provide new evidence for the existence of pharmacologically distinct intermediate conductance KCa channel in sensory afferent neurons.