Muscle palmitate uptake and binding are saturable and inhibited by antibodies to FABP(PM)

Studies show that uptake of long-chain fatty acids (LCFA) across the plasma membranes (PM) may occur partly via a carrier-mediated process and that th e plasma membrane fatty acid-binding protein (FABP(PM)) may be a component of this system. To test the hypothesis that FABP(PM) is involved in transsa rcolemmal transport of LCFA in muscle, we measured palmitate uptake in gian t sarcolemmal vesicles and palmitate binding to PM proteins in rat muscles, (1) in the presence of increasing amounts of unbound palmitate and (2) in the absence or presence of antibody to FABP(PM). Both palmitate uptake and binding were found to be saturable functions of the unbound palmitate conce ntration with calculated V-max values of 10.5 +/- 1.2 pmol/mg protein/15 se c and 45.6 +/- 2.9 nmol/mg protein/15 min and K-m values of 12.8 +/- 3.8 an d 18.4 +/- 1.8 nmol/L, respectively. The V-max values for both palmitate up take and binding were significantly decreased by 75-79% in the presence of a polyclonal antibody to the rat hepatic FABP(PM). Antibody inhibition was found to be dose-dependent and specific to LCFA. Glucose uptake was not aff ected by the presence of the antibody to FABP(PM). Palmitate uptake and bin ding were also inhibited in the presence of trypsin and phloretin. These re sults support the hypothesis that transsarcolemmal LCFA transport occurs in part by a carrier-mediated process and that FABP(PM) is a component of thi s process in muscle.