title: Selective inhibition of Cav3.3 T-type calcium channels by Galphaq/11-coupled muscarinic acetylcholine receptors.
abstract: T-type calcium channels play critical roles in controlling neuronal excitability, including the generation of complex spiking patterns and the modulation of synaptic plasticity, although the mechanisms and extent to which T-type Ca(2+) channels are modulated by G-protein-coupled receptors (GPCRs) remain largely unexplored. To examine specific interactions between T-type Ca(2+) channel subtypes and muscarinic acetylcholine receptors (mAChRS), the Cav3.1 (alpha(1G)), Cav3.2 (alpha(1H)), and Cav3.3 (alpha) T-type Ca(2+)(1I)channels were co-expressed with the M1 Galpha(q/11)-coupled mAChR. Perforated patch recordings demonstrate that activation of M1 receptors has a strong inhibitory effect on Cav3.3 T-type Ca(2+) currents but either no effect or a moderate stimulating effect on Cav3.1 and Cav3.2 peak current amplitudes. This differential modulation was observed for both rat and human T-type Ca(2+) channel variants. The inhibition of Cav3.3 channels by M1 receptors is reversible, use-independent, and associated with a concomitant increase in inactivation kinetics. Loss-of-function experiments with genetically encoded antagonists of Galpha and Gbetagamma proteins and gain-of-function experiments with genetically encoded Galpha subtypes indicate that M1 receptor-mediated inhibition of Cav3.3 occurs through Galpha(q/11). This is supported by experiments showing that activation of the M3 and M5 Galpha(q/11)-coupled mAChRs also causes inhibition of Cav3.3 currents, although Galpha(i)-coupled mAChRs (M2 and M4) have no effect. Examining Cav3.1-Cav3.3 chimeric channels demonstrates that two distinct regions of the Cav3.3 channel are necessary and sufficient for complete M1 receptor-mediated channel inhibition and represent novel sites not previously implicated in T-type channel modulation.
authors.affiliation: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hildebrand
authors.forename: Laurence S
authors.initials: LS
authors.lastname: David
authors.forename: Jawed
authors.initials: J
authors.lastname: Hamid
authors.forename: Kirk
authors.initials: K
authors.lastname: Mulatz
authors.forename: Esperanza
authors.initials: E
authors.lastname: Garcia
authors.forename: Gerald W
authors.initials: GW
authors.lastname: Zamponi
authors.forename: Terrance P
authors.initials: TP
authors.lastname: Snutch
mesh_terms: D000818:Animals; D001703:Biophysics / Q000379:methods; D002118:Calcium / Q000378:metabolism; D020747:Calcium Channels, T-Type / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D004594:Electrophysiology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
chemical_list: C469757:CACNA1I protein, human; D020747:Calcium Channels, T-Type; D026901:Membrane Transport Proteins; D011976:Receptors, Muscarinic; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D002118:Calcium