G-protein-independent modulation of P-type calcium channels by mu-opioids in Purkinje neurons of rat.
P-type calcium channels play a key role in the synaptic transmission between mammalian central neurons since a major part of calcium entering pre-synaptic terminals is delivered via these channels. Using conventional whole-cell patch clamp techniques we have studied the effect of mu-opioids on P-type calcium channels in acutely isolated Purkinje neurons from rat cerebellum. The selective mu-opioid agonist DAMGO (10nM) produced a small, but consistent facilitation of current through P-type calcium channels (10+/-1%, n=27, p<0.001). The effect of DAMGO was rapid (less than 10s) and fully reversible. This effect was both concentration and voltage-dependent. The EC(50) for the effect of DAMGO was 1.3+/-0.4nM and the saturating concentration was 100nM. The endogenous selective agonist of mu-opioid receptors, endomorphin-1 demonstrated similar action. Intracellular perfusion of Purkinje neurons with GTPgammaS (0.5mM) or GDPbetaS (0.5mM), as well as strong depolarizing pre-pulses (+50mV), did not eliminate facilitatory action of DAMGO on P-channels indicating that this effect is not mediated by G-proteins. Furthermore, the effect of DAMGO was preserved in the presence of a non-specific inhibitor of PKA and PKC (H7, 10microM) inside the cell. DAMGO-induced facilitation of P-current was almost completely abolished by the selective mu-opioid antagonist CTOP (100nM). These observations indicate that mu-type opioid receptors modulate P-type calcium channels in Purkinje neurons via G-protein-independent mechanism.
Iegorova
Olena
O
Bogomoletz Institute of Physiology, Department of Cellular Membranology, 4 Bogomoletz Street, Kiev 01024, Ukraine.
Fisyunov
Alexander
A
Krishtal
Oleg
O
D000818:Animals; D020865:Calcium Channels, P-Type / Q000502:physiology*; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011689:Purkinje Cells / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017450:Receptors, Opioid, mu / Q000819:agonists* / Q000037:antagonists & inhibitors; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D020865:Calcium Channels, P-Type; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; D013873:Thionucleotides; C105293:endomorphin 1; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C049352:phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013004:Somatostatin; C023427:guanosine 5'-O-(2-thiodiphosphate); D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019204:GTP-Binding Proteins