Cooling Reduces cAMP-Stimulated Exocytosis and Adiponectin Secretion at a Ca2+-Dependent Step in 3T3-L1 Adipocytes

We investigated the effects of temperature on white adipocyte exocytosis (measured as increase in membrane capacitance) and short-term adiponectin secretion with the aim to elucidate mechanisms important in regulation of white adipocyte stimulus-secretion coupling. Exocytosis stimulated by cAMP (included in the pipette solution together with 3 mM ATP) in the absence of Ca2+ (10 mM intracellular EGTA) was equal at all investigated temperatures (23 degrees C, 27 degrees C, 32 degrees C and 37 degrees C). However, the augmentation of exocytosis induced by an elevation of the free cytosolic [Ca2+] to similar to 1.5 mu M (9mMCa(2+) + 10 mM EGTA) was potent at 32 degrees C or 37 degrees C but less distinct at 27 degrees C and abolished at 23 degrees C. Adiponectin secretion stimulated by 30 min incubations with the membrane permeable cAMP analogue 8-Br-cAMP (1 mM) or a combination of 10 mu M forskolin and 200 mu M IBMX was unaffected by a reduction of temperature from 32 degrees C to 23 degrees C. At 32 degrees C, cAMP-stimulated secretion was 2-fold amplified by inclusion of the Ca2+ ionophore ionomycin (1 mu M), an effect that was not observed at 23 degrees C. We suggest that cooling affects adipocyte exocytosis/adiponectin secretion at a Ca2+-dependent step, likely involving ATP-dependent processes, important for augmentation of cAMP-stimulated adiponectin release.