Metabolism of C¹³-Carboxyl-Labeled Propionate by the Isolated, Perfused Dog Gastrocnemius

¹ From the Department of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota

The metabolism of C¹³-carboxyl-labeled propionate was studied in the isolated perfused dog gastrocnemius muscle, both resting and contracting. Under the conditions employed, 9–13% of the respiratory CO₂ was derived from the carboxyl carbon of propionate in the resting skeletal muscle preparation, and only 3–5% in the repetitively contracting gastrocnemius. Thus, during muscle activity, the carboxyl carbon of propionate contributed proportionally less to the metabolic mixture giving rise to CO₂ than during rest. Evidence was obtained for the conversion of carboxyl-labeled propionate to carboxyl-labeled lactate by isolated skeletal muscle, but not for its incorporation into muscle glycogen. When acetate and propionate are administered simultaneously to resting muscle, the rate of conversion of the carboxyl carbon of propionate to CO₂ is reduced to a much greater extent than that of the carboxyl carbon of acetate.

Note:
with the technical assistance of Joyce A. Swanson, Colleen Rehder and Ruth B. Deal