Functional coupling between human E-type Ca2+ channels and mu opioid receptors expressed in Xenopus oocytes

Neuronal alpha(1E) Ca2+ channels were expressed in Xenopus laevis oocytes alone and in combination with the mu opioid receptor. Macroscopic currents were recorded under voltage clamp conditions. The stimulation of the morphine receptor by the synthetic [D-Ala(2),N-Me-Phe(4),Gly-ol(5)] enkephalin (DAMGO) produced a 20% reduction in the alpha(1E) ionic current. This effect was associated with a large change in the decay phase of the Ba2+ current. The effect of 1 mu M DAMGO was fully antagonized by the universal mu opioid receptor antagonist naloxone and by the selective antagonist beta-funaltrexamine, The ionic current inhibition induced by DAMGO was partially recovered by preceding strong depolarizations. The injection of the catalytic subunit of pertussis toxin (A-protomer) abolished the effect of DAMGO, suggesting the involvement of a GTP binding protein in the alpha(1E) modulation. The coexpression of the regulatory beta(2a) Ca-2a channel subunit, together with the alpha(1E) subunit and the mu opioid receptor, prevented the reduction of the ionic current following the receptor stimulation with DAMGO, whereas the coexpression with the beta 3 subunit reduced by similar to 50% the modulatory effect of DAMGO. The effect produced by the stimulation of the opioid receptor could be mimicked by coexpressing the alpha(1E) channel with the G-protein beta gamma subunits, (C) 1998 Federation of European Biochemical Societies.