We have shown previously that insulin attenuates β1-adrenergic receptor (β1-AR)-mediated lipolysis viaactivation of protein kinase C (PKC) in rat adipocytes. This antilipolysis persists after removal of insulin and isindependent of the phosphodiesterase 3B activity, and phorbol 12-myristate 13-acetate (PMA) couldsubstitute for insulin to produce the same effect. Here, we attempted to identify the PKC isoform responsiblefor antilipolysis. Isolated adipocytes were treated with high and low concentrations of PMA for up to 6 h todegrade specific PKC isoforms. In the PMA-treated cells, the downregulation profiles of PKC isoforms α and βI,but not βII, δ, ɛ, or ζ, correlated well with a decrease of lipolysis-attenuating effect of PMA. After rats fastedfor 24 h, adipocyte expression of PKC isoform α increased, while expression of PKCδ decreased. Fasting didnot change the potency of PMA to attenuate lipolysis, however. The lipolysis-attenuating effect of PMA wasblocked by the PKCβI/βII inhibitor LY 333531, but not by the PKCβII inhibitor CGP 53353 or the PKCδ inhibitorrottlerin. These data suggest that PKCβI interacts with β1-AR signaling and attenuates lipolysis in ratadipocytes
