Nifedipine blocks calcium-dependent cholinergic depolarization in the guinea pig hippocampus.
The possibility that cholinergic stimulation might directly activate a receptor-operated Ca2+ channel was investigated in the CA1 region of guinea pig hippocampus using intracellular recording techniques. Two cholinergic responses were studied: (1) the plateau depolarization evoked by cholinergic stimulation in the presence of Ba2+; and (2) the Ca2(+)-dependent component of membrane depolarization. Both of these responses were blocked by 1-5 microM of nifedipine, a blocker of voltage-dependent L-type Ca2+ channels. In addition, the plateau response was mimicked by direct postsynaptic depolarization in the presence of Ba2+. We conclude that cholinergic stimulation does not directly activate a Ca2+ conductance in these neurons, but rather leads to the indirect activation of L channels which may be located both pre- and postsynaptically.
Blitzer
R D
RD
Psychiatry Service, Bronx V.A. Medical Center, NY 10468.
Gil
O
O
Omri
G
G
Landau
E M
EM
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D004594:Electrophysiology; D006168:Guinea Pigs; D006624:Hippocampus / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology*; D010275:Parasympathetic Nervous System / Q000502:physiology*; D013997:Time Factors
D001464:Barium; D002217:Carbachol; D009543:Nifedipine; D002118:Calcium