Nociceptin is a potent inhibitor of N-type Ca(2+) channels in rat sympathetic ganglion neurons

Nociceptin, an endogenous agonist of the opioid receptor-like(1) (ORL(1)) receptor, is implicated in a wide range of physiological functions including cardiovascular control. However, the effect of nociceptin on peripheral sympathetic ganglion neurons has not been studied. Whole-cell voltage clamp was used to study Ca(2+) currents on freshly dissociated sympathetic superior cervical ganglion neurons from juvenile rats. Nociceptin (1 microM) caused a fast inhibition of the peak currents by 69+/-3% in all neurons. Strong positive prepulses counteracted the inhibition of the peak current by 64% and no effect of nociceptin was observed when the cells were pre-incubated with Pertussis toxin. The inhibition was reversible and dose-dependent with an EC(50) of 508+/-50 pM. Blockade of N-type channels by 1 microM omega-conotoxin GVIA reduced the peak currents by 83+/-1% and abolished the action of nociceptin. Naloxone could not prevent the inhibition by nociceptin and [D-Ala(2), N-Me-Phe(4), Gly(5)-ol] enkephalin (DAMGO) only depressed a small proportion of the current in 1/7 neurons. These data suggests that nociceptin inhibits transmitter release from sympathetic neurons by a selective blockade of N-type channels, which may be of importance for its depressive effect on the cardiovascular system.