Abstract
Abstract The omission of K+ from the buffer used for isolation and incubation 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 by mitochondria, also blocked the increase in respiration due to 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++ and 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 K+-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.
Highlights
We have suggested that respiration is coupled to phosphorylation in brown fat cells under basal conditions but that the large increase in respiration seenafter the addition of lipolytic agents is due to an uncoupling action of lipolytic agents [5]
Fain found that potassium was not essential for the action of insulin on white fat cells [11] and that the activation of lipolysis by lipolytic agents could be influenced but was not dependent upon the presence of Kf in the medium [12]
If K+ was omitted from the phosphate buffer used for isolation, washing, and incubation of brown fat cells, there was no acceleration of respiration by epinephrine (Fig. 1) or theophylline (Table II) but basal respiration was only slightly affected
Summary
Brown fat cells were isolated from the dorsal interscapular brown adipose tissue of Sprague-Dawley female rats deprived of food for 18 hours prior to death. Brown fat cells were isolated by collagenase digestion of brown fat as described previously [5, 8]. The phosphate buffer was made up fresh daily and adjusted to pH 7.4 after the addition of 4~~ bovine Fraction V albumin powder (Pentex No 55). In some experiments (Tables VI to VIII) albumin defatted by the procedure of Guillory and Racker was used [3]. The regular phosphate buffer contained the following: NaCI, 128 mM; CaC!&, 1.4 mM; MgS04, 1.4 mM; KCl, 5.2 mM; and NazHPO+ 10 mM (pH adjusted to 7.4 with HCl). Buffers deficient in K+, Ca++, or Mg+f were made in the same manner, but with the appropriate cation omitted
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
