Measurement of rat heart fatty acid binding protein by ELISA. Tissue distribution, developmental changes and subcellular distribution.

A class of soluble, low molecular weight proteins collectively called fatty acid binding proteins (FABP) are thought to function in the intracellular movement of fatty acids. To understand more clearly the role of FABP in cardiac metabolism, we used ELISA and immunoblotting techniques to study the distribution of heart FABP in several rat tissues, compare male and female rat heart content, quantitate developmental changes, and determine its subcellular distribution. Immunoreactive protein was found in appreciable amounts in rat heart, red skeletal muscle and kidney. Adult rat heart contained about 1.5 mg FABP/g tissue wet weight with the atrial content being approximately 50% of the ventricular concentration. No significant difference was detected between the sexes. The amount of FABP increased progressively during development from fetal to adult animals, and measureable amounts were found in 17-day-old fetal tissue. Comparisons between myoglobin and FABP showed that FABP appeared earlier than myoglobin in development, but myoglobin was more abundant than FABP at birth. Using immunoblots it was determined that rat heart FABP was localized in the cytosol with no detectable intramitochondrial material.