Suppression of β-adrenergic responsiveness of L-type Ca2+current by IL-1β in rat ventricular myocytes

The possible mechanism by which interleukin-1beta (IL-1beta) affects beta-adrenergic responsiveness of L-type Ca2+ current (ICa,L) was examined in adult rat ventricular myocytes by use of whole cell patch-clamp techniques. In the presence of isoproterenol (Iso), exposure for 3 min to IL-1beta suppressed the Iso-activated ICa,L. In the presence of IL-1beta, the response of ICa,L to Iso was decreased, and the EC50 for Iso stimulation was increased. However, IL-1beta had no effect on [3H]CGP-12177 binding, displacement of [3H]CGP-12177 binding by Iso, or on basal and Iso-enhanced cAMP content. When ICa,L was activated by extracellular application of forskolin or 8-(4-chlorophenylthio)-cAMP, a membrane-permeable cAMP analog, or by intracellular dialysis with cAMP, IL-1beta had little effect on ICa,L. In contrast, in the presence of cAMP, IL-1beta still suppressed the Iso-enhanced ICa,L. These results show that the IL-1beta-induced decrease in beta-adrenergic responsiveness of ICa,L does not result from inhibition of beta-adrenoceptor binding, adenylyl cyclase activity, or cAMP-mediated pathways, suggesting a cAMP-independent mechanism.