Characterization of a calcium current in a vertebrate cholinergic presynaptic nerve terminal.
Calcium currents were recorded from a cholinergic presynaptic nerve terminal in the chick ciliary ganglion using the whole-cell voltage-clamp technique. The presynaptic element of this synapse is in the form of a calyx that envelops the postsynaptic ciliary neuron. A method was developed to isolate the ciliary neuron, expose the calyx, and apply patch-clamp electrodes under visual control. The presynaptic Ca current activated at +30 mV with a fast time constant of about 1.5 msec and deactivated at -80 mV with a time constant of about 0.5 msec, values that are consistent with a role in action-potential-dependent transmitter release. The calyx Ca current was blocked by 0.1 mM Cd or 2 microM omega-conotoxin and was resistant to voltage-dependent inactivation. The presynaptic Ca channel exhibits similarities to the N-type group but differs from these by the minimal voltage-dependent inactivation. This type of channel, designated CaN-PT (N-like, presynaptic terminal), may play a key role in transmitter release at many vertebrate fast-transmitting synapses.
Stanley
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EF
NINDS Biophysics Laboratory, National Institutes of Health, Bethesda, Maryland 20892.
Goping
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G
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002642:Chick Embryo; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D005726:Ganglia, Parasympathetic / Q000166:cytology; D006652:Histological Techniques; D009411:Nerve Endings / Q000502:physiology*; D009474:Neurons / Q000166:cytology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D012583:Schwann Cells; D013569:Synapses / Q000502:physiology*
D002104:Cadmium; D002118:Calcium