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 -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 μM ryanodine. Met-enkephalin (10 μM) evoked a similar increase in BK(Ca) channel activity, which was dependent on the presence of extracellular Ca2+ and inhibited by either ryanodine (10 μM) or naloxone (1 μM). In Fura-2-loaded intracardiac neurones, Met-enkephalin evoked a transient increase in [Ca2+](i), Met-enkephalin-induced mobilization of intracellular Ca2+ may play a role in neuronal excitability and firing behaviour in mammalian intracardiac ganglia.