Arachidonic acid may mediate the galanin-induced hyperpolarization in parasympathetic neurons from Necturus maculosus

The effects of arachidonic acid (AA) and compounds that inhibit intracellular signalling pathways on membrane potential and galanin-induced hyperpolarizations were investigated in parasympathetic neurons from Necturus maculosus. Treatment for 10-90 min with 10-20 microM 4-bromophenacylbromide or 10 microM cyclosporin A caused a progressive decrease in the amplitude of galanin-induced hyperpolarizations without any change in resting membrane potential. The galanin-induced hyperpolarization was not altered following a 10-120 min treatment with the protein kinase inhibitor H-7. These results indicated that phospholipase A2 activation, but not protein kinase activation, may be required for the galanin-induced hyperpolarization. Arachidonic acid (20-100 microM) caused a concentration-dependent membrane hyperpolarization of the parasympathetic neurons and a decrease in the amplitude of the galanin-induced hyperpolarization. These data indicate that phospholipase A2-catalyzed liberation of AA may be involved in the galanin-induced membrane hyperpolarization observed in mudpuppy parasympathetic neurons.