Potassium-depolarization-induced cytoplasmic [Ca²⁺] transients in freshly dissociated pyramidal neurones of the rat dorsal cochlear nucleus

Abstract.

The significance of voltage-activated Ca²⁺ currents in eliciting cytoplasmic Ca²⁺ transients was studied in pyramidal neurones isolated from the rat dorsal cochlear nucleus using combined enzyme treatment/mechanical trituration. Increases in cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) were evoked by K⁺-induced depolarizations (10–50 mM) and monitored by the Fura-2 fluorimetric technique. The acutely dissociated neurones had a resting [Ca²⁺]_i of 17.2±0.5 nM. They possessed caffeine-sensitive Ca²⁺ stores which were empty at rest; these stores could be filled with Ca²⁺ entering from the extracellular space and were re-emptied quickly. The effects of various specific high-voltage-activated (HVA) Ca²⁺ channel antagonists (nifedipine, ω-agatoxin IVA and ω-conotoxin GVIA) on [Ca²⁺]_i transients were tested. Analysis of the blocking effects of these agents on the [Ca²⁺]_i transients indicates that, in the pyramidal neurones of the dorsal cochlear nucleus, N-type Ca²⁺ channels are primarily responsible for producing the depolarization-induced increases in [Ca²⁺]_i.