A-and Fl-adrenergic Mediation of Changes in Metabolism and Na/k Exchange in Rat Brown Fat

Doubleand triple-barreled ion-sensitive microelectrodes were used to measure changes in extracellular K+ and Na' concentrations ([K+]o, [Na'].) in brown fat . Redox states of different respiratory enzymes were measured simultaneously in order to correlate ion movements with metabolic activity . Trains of stimuli applied to the efferent nerves evoked two distinct increases in [K']o . A first, small, rapid increase occurred within 10 s and accompanied a first, rapid membrane depolarization . A second, slow increase of [K*]a occurred several minutes after stimulation and accompanied a second, slow depolarization . A few seconds after stimulation onset, while the membrane was repolarizing and shifts in redox states indicated increases in lipolysis and respiration, [K''] o decreased . The [K+ ]o decrease was accompanied by an increase in [Nay']o, and could be partly blocked by ouabain . Phentolamine, an a-antagonist that blocks the first depolarization, also blocked the first, rapid [K* ]o increase and part of the subsequent decrease. Propranolol, a S-antagonist, had little effect on the first depolarization and the first increase in [K''']o, but blocked part of the subsequent [K+]o decrease and the second, slow [K+ ]o increase . The changes in [K+ ]o were almost completely abolished in the presence of both antagonists . It is concluded that brown adipocytes take up K+ and simultaneously lose Na' in response to the interaction of noradrenaline with aand Sreceptors, and this indicates a very early stimulation of the Na' pump.