Attenuation of G protein-mediated inhibition of N-type calcium currents by expression of caveolins in mammalian NG108-15 cells.
1. Caveolins are integral proteins of glycolipid/cholesterol-rich plasmalemmal caveolae domains, where, they may function as a plasma membrane scaffold onto which many classes of signalling molecules, including receptors and heterotrimeric G proteins, can assemble. To ascertain whether caveolins influence G protein-mediated signal transduction, we stably expressed caveolin-1 and -3 isoforms in the neuroblastoma x glioma NG108-15 hybrid cell line, lacking endogenous caveolins. Subsequently, using whole-cell voltage clamp methods, we examined whether the modulation of N-type voltage-gated Ca2+ channels by G(o) protein-coupled, delta-type opioid receptors might be affected by recombinant caveolin expression. 2. In transfected NG108-15 cells, caveolins localized at the plasma membrane and, upon subcellular fractionation on sucrose density gradients, they co-localized in Triton-resistant, low buoyancy fractions, with endogenous G(o) protein alpha-subunits. 3. The voltage-dependent inhibition of omega-conotoxin GVIA-sensitive Ba2+ currents following either activation of delta-opioid receptors by the agonist [o-pen2,o-pen5]-enkephalin (DPDPE), or direct stimulation of G proteins with guanosine 5'-O-(thiotriphosphate) (GTPgammaS) was significantly attenuated in caveolin-expressing cells. The kinetics of Ca2+ channel inhibition were also modified by caveolins. 4. Overall, these results suggest that caveolins may negatively affect G protein-dependent regulation of voltage-gated N-type Ca2+ channels, presumably by causing a reduction of the available pool of activated G proteins.
Toselli
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Department of Cellular and Molecular Physiological and Pharmacological Sciences, and INFM, University of Pavia, Via Forlanini 6, I-27100 Pavia, Italy. mtoselli@unipv.it
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D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D051242:Caveolin 1; D051244:Caveolin 3; D022461:Caveolins / Q000235:genetics* / Q000378:metabolism*; D004594:Electrophysiology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D005910:Glioma; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006822:Hybrid Cells; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009447:Neuroblastoma; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D000701:Analgesics, Opioid; D020864:Calcium Channels, N-Type; C495537:Cav1 protein, rat; C495549:Cav3 protein, rat; D051242:Caveolin 1; D051244:Caveolin 3; D022461:Caveolins; D011994:Recombinant Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020881:Enkephalin, D-Penicillamine (2,5)-; D019204:GTP-Binding Proteins