Multiple voltage-dependent calcium currents in acutely isolated mouse vestibular neurons.

ABSTRACT

We investigated the presence of voltage-gated calcium currents in vestibular neurons acutely isolated from postnatal mice vestibular ganglions using the whole-cell patch-clamp technique. The neuronal origin of the recorded cells was confirmed by immunohistochemical detection of neurofilaments and calretinin. High and low voltage-activated calcium currents were recorded. High voltage-activated currents were present in all investigated neurons. Low voltage-activated currents were recorded in only a few large vestibular neurons. High and low voltage-activated currents were distinguished by their thresholds of activation and their ability to run-up during early recordings. Among high voltage-activated currents. L-, N- and P-type currents were identified by their sensitivity to, respectively, the dihydropyridines agonist Bay K 8644 (3 microM) and antagonist nitrendipine (3 microM), the co-conotoxin GVIA (3 microM) and the omega-agatoxin IVA at low concentration (50 nM). An inactivating current sensitive to 1 microM omega-agatoxin IVA with characteristics similar to those of the Q-type current was also recorded in vestibular neurons. When L-, N-, P-, Q-type barium currents were blocked, a residual high voltage-activated current defined by its resistance to saturating concentrations of all above blockers was detected. This residual current was completely blocked by 0.5 mM nickel and cadmium. Our results reveal that primary vestibular neurons express a variety of voltage-activated calcium currents with distinct physiological and pharmacological properties. This diversity could be related both with their functional synaptic characteristic, and with the intrinsic physiological properties of each class of vestibular afferents.