The regulating manner of opioid receptors on distinct types of calcium channels in hamster submandibular ganglion cells

It is well known that opioids produce inhibitory effects on neuronal activity and on synaptic transmission at most synapses. In this study, we have investigated the effects of opioids on the low voltage and high voltage activated calcium channels in acutely dissociated submandibular ganglion (SMG) neurons, using the whole-cell configuration of the patch clamp technique. The κ-opioid-receptor agonist U-50488H, the δ-opioid-receptor agonist [D-Pen2,5]- enkephalin and the μ-opioid-receptor agonist [D-Ala2, N-Me-Phe4, Gly5 -ol]-enkephalin inhibited L-, N- and P/Q-type calcium-current components in a dosedependent manner at 10 nM–1 mM, respectively, but not the T-type calcium current. These inhibitory effects were antagonized by naloxone (1 mM). The results showed that three types of opioid receptors regulate the L-, N- and P/Q-types of calcium channels, respectively, but not the T-type, in SMG neurones.