CA2-TRAINED RATS( AND LIPOLYSIS IN ADIPOCYTES FROM EXERCISE)

The effects of Ca2+ on lipolysis and protein kinase activity in adipoc ytes from exercise-trained rats were investigated. Chronic exercise si gnificantly increased lipolytic responses to norepinephrine and dibuty ryl adenosine 3',5'-cyclic monophosphate (cAMP). The inhibitory effect s of N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7), a calu modulin inhibitor, on norepinephrine- and dibutyryl cAMP-stimulated li polysis were significantly greater in trained than in sedentary rats. Training did not alter cAMP-dependent protein kinase activity. However , the inhibitory effect of W-7 on cAMP-dependent protein kinase activi ty was much greater in trained than in sedentary rats. The basal intra cellular free Ca2+ concentration ([Ca2+](i)) was significantly higher in trained than in sedentary rats. The rapid and transient increases i n [Ca2+](i) due to adrenocorticotropic hormone and phenylephrine from basal levels were significantly lower in trained than in sedentary rat s. However, the higher basal [Ca2+](i) level in trained rats led to in creases in sustained [Ca2+](i) levels after stimulation. We concluded that in trained rats the regulation of protein kinase activity by cAMP depends to a greater degree on Ca2+-calmodulin complex than it does i n sedentary rats and that training alters adipocyte intracellular Ca2 homeostasis, including [Ca2+](i) responsiveness to hormones.