Abstract
The possibility that cholinergic stimulation might directly activate a receptor-operated Ca 2+ 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 Ba 2+; and (2) the Ca 2+-dependent component of membrane depolarization. Both of these responses were blocked by 1–5 μM of nifedipine, a blocker of voltage-dependent L-type Ca 2+ channels. In addition, the plateau response was mimicked by direct postsynaptic depolarization in the presence of Ba 2+. We conclude that cholinergic stimulation does not directly activate a Ca 2+ conductance in these neurons, but rather leads to the indirect activation of L channels which may be located both pre- and postsynaptically.
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