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* To whom correspondence should be addressed. E-mail: alimonru{at}uci.edu.
Vestibular-afferent neurons transmit information about linear and angular accelerations during head movements from vestibular end-organs to vestibular nuclei. In situ, these neurons show heterogeneous discharge patterns that may be produced by differences in their intrinsic properties. However, little is known about the ionic currents underlying their different firing patterns. Using the whole-cell patch-clamp technique, we analyzed the expression of Ca2+ and Ca2+-activated K+ currents (IKCa) in primary cultured neurons isolated from young rats (p7 - p10). We found two overlapping subpopulations of vestibular-afferent neurons (VANs) classified according to low threshold Ca2+current (LVA) expression; LVA (-) neurons, formed by small cells, and LVA (+) neurons composed of medium to large cells. The IKCa in both cell-groups was carried through channels of high (BK), intermediate (IK), and low conductance (SK), besides a resistant channel to classical blockers (IR). BK was expressed preferentially in LVA (+) cells, whereas IR expression was preferentially in LVA (-) cells. No correlation between SK and IK expression with the soma size was found. Current clamp experiments showed that BK participates in the adaptation of discharge and in the duration of the action potential, whereas SK and IK did not show a significant contribution to electrical discharge of cultured VANs. However, because of the low number of VANs in culture with repetitive firing it is difficult to interpret our results in terms of discharge patterns. Our results demonstrate that vestibular-afferent neurons possess different Ca2+ activated K+ (KCa) channels and that their expression, heterogeneous among the cells, would contribute to explain some of the differences in the electrical-firing properties of these neurons.
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