Differential facilitation of N- and P/Q-type calcium channels during trains of action potential-like waveforms.
Inhibition of presynaptic voltage-gated calcium channels by direct G-protein betagamma subunit binding is a widespread mechanism that regulates neurotransmitter release. Voltage-dependent relief of this inhibition (facilitation), most likely to be due to dissociation of the G-protein from the channel, may occur during bursts of action potentials. In this paper we compare the facilitation of N- and P/Q-type Ca(2+) channels during short trains of action potential-like waveforms (APWs) using both native channels in adrenal chromaffin cells and heterologously expressed channels in tsA201 cells. While both N- and P/Q-type Ca(2+) channels exhibit facilitation that is dependent on the frequency of the APW train, there are important quantitative differences. Approximately 20 % of the voltage-dependent inhibition of N-type I(Ca) was reversed during a train while greater than 40 % of the inhibition of P/Q-type I(Ca) was relieved. Changing the duration or amplitude of the APW dramatically affected the facilitation of N-type channels but had little effect on the facilitation of P/Q-type channels. Since the ratio of N-type to P/Q-type Ca(2+) channels varies widely between synapses, differential facilitation may contribute to the fine tuning of synaptic transmission, thereby increasing the computational repertoire of neurons.
Currie
Kevin P M
KP
Department of Neurobiology, Pharmacology and Physiology, University of Chicago, 947 E. 58th Street, MC 0926, Chicago, IL 60637, USA. kevin@drugs.bsd.uchicago.edu
Fox
Aaron P
AP
D000200:Action Potentials / Q000502:physiology; D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D020864:Calcium Channels, N-Type / Q000502:physiology*; D020865:Calcium Channels, P-Type / Q000502:physiology*; D020907:Calcium Channels, Q-Type / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D004558:Electric Stimulation; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011994:Recombinant Proteins / Q000378:metabolism
D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D018377:Neurotransmitter Agents; D011994:Recombinant Proteins