Met-enkephalin-induced mobilization of intracellular Ca2+ in rat intracardiac ganglion neurones.
The effects of Met-enkephalin on Ca2+-dependent K+ channel activity were investigated using the cell-attached patch recording technique on isolated parasympathetic neurones of rat intracardiac ganglia. Large-conductance, Ca2+-dependent K+ channels (BK(Ca)) were examined as an assay of agonist-induced changes in the intracellular free calcium ion concentration ([Ca2+]i). These BK(Ca) channels had a conductance of approximately 200 pS and were charybdotoxin- and voltage-sensitive. Caffeine (5 mM), used as a control, evoked a large increase in BK(Ca) channel activity, which was inhibited by 10 microM ryanodine. Met-enkephalin (10 microM) evoked a similar increase in BK(Ca) channel activity, which was dependent on the presence of extracellular Ca2+ and inhibited by either ryanodine (10 microM) or naloxone (1 microM). In Fura-2-loaded intracardiac neurones, Met-enkephalin evoked a transient increase in [Ca2+]i. Met-enkephalin-induced mobilization of intracellular Ca+ may play a role in neuronal excitability and firing behaviour in mammalian intracardiac ganglia.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D018999:Charybdotoxin / Q000494:pharmacology; D004594:Electrophysiology; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D005724:Ganglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006329:Heart Conduction System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology