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The Journal of Neuroscience, May 1, 2000, 20(9):3115-3128
Reluctant Gating of Single N-Type Calcium Channels during Neurotransmitter-Induced Inhibition in Bullfrog Sympathetic Neurons
Hye Kyung Lee2 and Keith S. Elmslie1 1 Department of Physiology, Tulane University Medical School, New Orleans, Louisiana 70112, and 2 Department of Pharmacology, Chonbuk University Dental School, Chonju, Korea 561-756
Whole-cell recordings have been used to extensively characterize the voltage-dependent inhibition of N-type calcium current induced by various neurotransmitters. Results from these studies have yielded several predictions on the effect of inhibition on N-channel gating, namely delayed channel opening and inhibition-induced reluctant openings. Previous single N-channel studies observed delayed channel opening but failed to find reluctant openings. However, strong depolarizations may be necessary to see reluctant openings, but this was not tested. We have examined N-channel gating at voltages depolarized to those used previously and found a neurotransmitter-induced open state that has properties predicted for the reluctant open state. The openings had lower open probability (Po) and brief open times compared to the dominant gating state observed in control (high Po). These reluctant events were reduced after strong depolarizing pulses used to reverse inhibition. The threshold voltage for activation of reluctant events was ~30 mV depolarized to that of the normal gating state (high Po). However, an action potential will provide sufficient depolarization to open reluctant N-channels.
Key words: cell-attached; patch-clamp; single Ca2+ channel; N-type calcium current; norepinephrine; willing-reluctant model
Copyright © 2000 Society for Neuroscience 0270-6474/00/2093115-14$05.00/0
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