Toxin-insensitive Ca current in dorsal raphe neurons.
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.
Penington
N J
NJ
Department of Pharmacology, State University of New York, Brooklyn 11203-2098, USA.
Fox
A P
AP
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D004553:Electric Conductivity; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D009553:Nimodipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D011903:Raphe Nuclei / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology; D014118:Toxins, Biological / Q000494:pharmacology*; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D013111:Spider Venoms; D014118:Toxins, Biological; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; D009553:Nimodipine; D020866:omega-Conotoxin GVIA; D002118:Calcium