Potassium-dependent stimulation of respiration in brown fat cells by fatty acids and lipolytic agents.

The omission of K+ from the buffer used for isolation and it .cubation of rat brown fat cells blocked the large increases in respiration seen after the addition of lipolytic agents. The effect of K+ was on the activation of respiration by free fatty acids rather than upon the lipolytic action of agents such as theophylline. Rb+ and Cs+, but not NH4+, could partially substitute for K+ in the activation of respiration by theophylline. Valinomycin, an antibiotic which activates the uptake of K+ by isolated mitochondria, markedly stimulated respiration in brown fat cells in the presence but not in the absence of K+. Nigericin, another antibiotic which blocks K+ uptake hy mitochondria, also blocked the increase in respiration due L+ valinomycin and theophylline. The effects of lipolytic agents on respiration could be mimicked by addition of albumin-bound free fatty acids to brown fat cells, an effect which was also K+-dependent. The omission of Ca++ a6d Mg++ reduced the activation of respiration by fatty acids or lipolytic agents. These findings indicate that the activation of energy metabolism by fatty acids involves a I(+-dependent process which is influenced by divalent cations. The increased oxygen consumption may be secondary to utilization of high energy intermediates of oxidative phosphorylation for increased K+ flux across membranes.