INCREASED [LACTATE] IN WORKING DOG MUSCLE REDUCES TENSION DEVELOPMENTINDEPENDENT OF PH

The purpose of this work was to examine the effect of the lactate ion on the fatigue process in working muscle independent of muscle [H+]. L -(+)-lactate was infused, at a pH that did not change arterial pH, int o the blood perfusing an isolated, in situ dog gastrocnemius (N = 5) w orking at a submaximal intensity (isometric contractions at 2 Hz) and compared with control (C) conditions without lactate infusion. Each mu scle was stimulated to work for two 60-min periods (separated by 45 mi n rest), consisting of three 20-min time periods with either the high arterial lactate condition (high [La]) or C condition sequentially ord ered within each 60-min work period. Blood flow and O-2 delivery were held constant between the C and high [La] conditions. Arterial and ven ous blood measurements and muscle biopsies were taken (7 biopsies from each condition) during each condition. Lactate infusion significantly increased arterial [La] (C = 4.2 +/- 0.2 mM vs high [La] = 14.4 +/- 0 .2; (X) over bar +/- SE) and muscle [La] (C = 8.1 +/- 0.8 mM w.w, vs h igh [La] = 12.0 +/- 1.4) while arterial and muscle pH were unchanged b etween conditions. Muscle tension development was significantly reduce d (C = 94 +/- 2 N . 100 g(-1) vs high [La]=80 +/- 3) during lactate in fusion and muscle O-2 uptake changed proportionally with tension. Thes e findings support an effect of the lactate anion on tension developme nt which is independent of pH.