CaVbeta subunit-mediated up-regulation of CaV2.2 currents triggered by D2 dopamine receptor activation.
Voltage-dependent Ca(2+) channels (VDCCs) are subject to modulation by a number of pathways, including membrane-delimited inhibition by heterotrimeric G-proteins and modulation through phosphorylation by diverse kinases. Here we report that in the Xenopus oocyte expression system Ca(V)2.2 channels undergo a sustained, linear and irreversible run-up lasting up to 30 min, which is potentiated during G-protein-mediated inhibition by activation of co-expressed G-protein coupled receptors (GPCRs). This up-regulation is not a result of receptor desensitization, but is associated with a hyperpolarization of the voltage for activation and depends on the presence of accessory subunits such that beta subunits promote, and alpha2delta subunits oppose the current increase. We have investigated the involvement of G-proteins and found that over-expression of Galpha(o) subunits or Galpha-transducin reduced the amount of agonist-mediated up-regulation. However, we have found no evidence for the involvement of any second messenger pathways in the increase of current run-up in the presence of a GPCR agonist. Taken together, our data suggest that the effect reported herein involves an enhancement of the GTPase activity of endogenous Galpha subunits, which is triggered by GPCR activation and mediated by accessory Ca(V)beta subunits. It may involve an increased association of Ca(V)beta subunits with alpha1 subunits in the plasma membrane or trafficking of channels to the plasma membrane.
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Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK. c.canti@ucl.ac.uk
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D000818:Animals; D015220:Calcium Channels / Q000096:biosynthesis*; D018491:Dopamine Agonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis
D015220:Calcium Channels; D018491:Dopamine Agonists; D017448:Receptors, Dopamine D2