Cyclic-AMP regulation of calcium-dependent K channels in an insect central neurone

Abstract In the cockroach fast coxal depressor motoneurone, either the muscarinic agonist McN-A-343 or dibutyryl cAMP (Db-cAMP) induced a reduction in voltage-dependent outward current. The response to McN is due to suppression of a calcium-dependent potassium current ( I K,Ca ) produced secondarily to a reduction in voltage-dependent calcium current ( I ca ). The response to Db-cAMP was investigated in order to establish whether cAMP might mediate the response to McN. I ca was suppressed by 3-isobutyl-l-methylxanthine (IBMX) but not by Db-cAAMP The effects of IBMX were therefore unlikely to be the result of phosphodiesterase inhibition. Since caffeine also suppressed I ca , the observed effect of IBMX is probably due to release of Ca 2+ from intracellular stores. I K,Ca , evoked by injection of Ca 2+ was reduced by Db-cAMP or forskolin but not by McN. These results indicate that the electrical response to McN in this neurone is not mediated by changes in cAMP.