Increased [lactate] in working dog muscle reduces tension development independent 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, into the blood perfusing an isolated, in situ dog gastrocnemius (N = 5) working at a submaximal intensity (isometric contractions at 2 Hz) and compared with control (C) conditions without lactate infusion. Each muscle was stimulated to work for two 60-min periods (separated by 45 min rest), consisting of three 20-min time periods with either the high arterial lactate condition (high [La]) or C condition sequentially ordered within each 60-min work period. Blood flow and O2 delivery were held constant between the C and high [La] conditions. Arterial and venous 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; mean +/- SE) and muscle [La] (C = 8.1 +/- 0.8 mM w.w. vs high [La] = 12.0 +/- 1.4) while arterial and muscle pH were unchanged between conditions. Muscle tension development was significantly reduced (C = 94 +/- 2 N.100 g-1 vs high [La] = 80 +/- 3) during lactate infusion and muscle O2 uptake changed proportionally with tension. These findings support an effect of the lactate anion on tension development which is independent of pH.