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

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.