Journal of Neuroscience, Vol 15, 5719-5726, Copyright © 1995 by Society for Neuroscience
Toxin-insensitive Ca current in dorsal raphe neurons
NJ Penington and AP Fox
Department of Pharmacology, State University of New York, Brooklyn 11203-2098, USA.
About 54% of the whole-cell Ca current recorded in dorsal raphe neurons
cannot be categorized as N-, L-, or P-type Ca current. This current,
ICa-Raphe, was not blocked by a combination of nimodipine, omega-CgTx-
GVIA, and omega-AGA-IVA. Differences in toxin sensitivity and voltage
dependence suggest that ICa-Raphe is distinct from Q- or R-type Ca
currents. In raphe neurons activation of 5-HT1A receptors by 5-HT inhibits
approximately 50% of the Ca current and slows activation. 5-HT inhibits
both N-type Ca channels and ICa-Raphe channels by approximately 50% and
slows the activation of both currents to a similar extent. Other
similarities between ICa-Raphe and N-type Ca current were observed; they
are both blocked to a similar extent by Ni2+, their activation properties,
their current kinetics and channel availability as a function of holding
potential are almost identical. Thus, ICa-Raphe represents a current that
is not sensitive to known antagonists, but which is similar to N-type Ca
current. Although it is possible that ICa-Raphe belongs to a heretofore
undiscovered family of Ca channels it is also possible that it represents
an omega-CgTx GVIA- insensitive isoform of the N-type Ca channel family.