Fatty acid uptake by isolated rat heart myocytes represents a carrier-mediated transport process

Abstract

The mechanism by which fatty acids enter cardiomyocytes is unclear. Therefore, the influx kinetics of [3H]oleate into isolated rat heart myocytes were examined. Cells were incubated at 37°C with [3H]oleate bound to albumin in various molar ratios and the initial rate of uptake (V0) was determined as a function of the unbound oleate concentration in the medium. V0 was saturable with increasing oleate concentrations incubated (K(m) 78 nM; V(max) 1.9 nmol x min-1 per 106 cells) and temperature dependent with an optimum at 37°C. Furthermore, binding of [3H]oleate to isolated plasma membranes of cardiomyocytes was saturable, revealing a K(D) of 42 nM, and was inhibited by heat denaturation or trypsin pretreatment of the membranes. From these membranes a single 40-kD protein with high affinity for a variety of long chain fatty acids was isolated. With a monospecific antibody to this membrane protein, binding as well as cellular influx of [3H]oleate was selectively inhibited. These data indicate that at least a portion of myocardial fatty acid uptake is mediated by a specific membrane protein.