Activation of enkephalin receptors reduces calcium conductance in neuroblastoma cells.
Enkephalin actions on the voltage-gated Ca channel were studied under voltage clamp in the neuroblastoma X glioma hybrid cell line, NG 108-15. We found that in sodium-free external solutions containing Ba2+ (20 mM), a depolarizing step pulse from a holding potential of -50 mV evoked both a rapidly decaying inward current and a sustained inward current similar to those described in other preparations. External application of 1 microM [D-Thr2,Leu5]enkephalin-Thr (DTLET), an agonist at the delta-opioid receptors specifically inhibited the sustained inward current. Naloxone, an antagonist at this receptor, blocked the effect of DTLET. Furthermore, this effect of DTLET was not observed if the cells were dialyzed with a low Ca2+ internal buffer solution [( Ca2+]i less than 10(-9) M). We conclude that in neuroblastoma cells: (1) there is a functional coupling between delta-receptors and voltage-gated sustained Ca channels, and (2) the coupling is mediated by intracellular free Ca ions.
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009447:Neuroblastoma; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D011957:Receptors, Opioid / Q000502:physiology*; D017465:Receptors, Opioid, delta
D007473:Ion Channels; D009842:Oligopeptides; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; C037653:deltakephalin; D002118:Calcium