Uptake and esterification of palmitrate by rat diaphragm in vitro.

The contribution of exogenously supplied palmitate to the intracellular palmitate pool and its role in esterification were studied for the intact rat diaphragm in vitro. Palmitate-1-(14)C attached to albumin in various molar ratios (nu) was taken up by the tissue in an initial rapid phase which led, after 4 min, to a steady-state level of tissue free fatty acid. The level was determined by nu but also by the albumin concentration below 2 g/100 ml. The exogenous palmitate taken up constitutes one-quarter to three-quarters of the intracellular palmitate pool as nu is increased from 0.5 to 5.5 (albumin concentration 2 g/100 ml). Turnover rates of intracellular palmitate at a given nu are stable over 35 min of incubation, as indicated by constant rates of esterification (largely to triglyceride, but also to phospholipids) and by the unchanging specific activity ratios between intracellular and medium palmitate-1-(14)C. These ratios also indicate that only a portion of the palmitate taken up is available for exchange with the albumin complex in the medium. Calculation of esterification rates at various nu values suggests that not all of the palmitate is in a pool that is available for esterification.