INTRACELLULAR PH IN ADIPOCYTES - EFFECTS OF FREE FATTY-ACID DIFFUSIONACROSS THE PLASMA-MEMBRANE, LIPOLYTIC AGONISTS, AND INSULIN

The main function of white adipose tissue is to store nutrient energy in the form of triglycerides. The mechanism by which free fatty acids (FFA) move into and out of the adipocyte has not been resolved, We sho w here that changes in intracellular pH (pH(i)) in adipocytes correlat e with the movement of FFA across cellular membranes as predicted by t he Kamp and Hamilton model of passive diffusion of FFA, Exposure of fa t cells to lipolytic agents or external FFA results in a rapid intrace llular acidification that is reversed by metabolism of the FFA or its removal by albumin, In contrast, insulin causes an alkalinization of t he cell, consistent with its main function to promote esterification, Inhibition of Na+/H+ exchange in adipocytes does not prevent the chang es in pH(i) caused by FFA, lipolytic agents, or insulin. A fatty acid dimer, which diffuses into the cell but is not metabolized, causes an irreversible acidification, Taken together, the data suggest that chan ges in pH(i) occur in adipocytes in response to the passive diffusion of un-ionized FFA (flip-flop) into and out of the cell and in response to their metabolism and production within the cell. These changes in pH(i) may, in turn, modulate hormonal signaling and metabolism with si gnificant impact on cell function.