Effects of flow and contraction on lactate transport in the perfused rat hindlimb
Watt, P.W.; Gladden, L.B.; Hundal, H.S.; Crawford, R.E.
American Journal of Physiology 267(1 Pt 1): E7-13
1994
ISSN/ISBN: 0002-9513 PMID: 8048516 Document Number: 433195
A perfused rat hindlimb preparation was used to assess the effects of perfusate flow and electrical stimulation to mimic exercise on the rates of lactate influx (measured by a dual tracer technique with (3H)mannitol as the extracellular marker) and net lactate production. The same perfused muscle system was also used for assessing the effects of alpha-cyano-4-hydroxycinnamate (CIN, 15 mM), phloretin (0.6 mM), and pyruvate on tracer lactate influx. Unidirectional lactate influx, oxygen uptake ( ovrhdot VO-2), and net lactate flux were all significantly dependent on perfusate flow rate (all P lt 0.05). The hindlimb was in net lactate production at all flow rates studied. Electrical stimulation (60 Hz, 100 ms, 20 V trains at 0.6 min-1) at perfusate lactate concentration of 1 mM significantly increased the hindlimb ovrhdot VO-2 from 8.0 +- 1.1 to 16.0 +- 2.2 ml cntdot kg-1 cntdot min-1 and production of lactate from -69 +- 31 to -823 +- 77 nmol cntdot min-1 cntdot g-1 (both P lt 0.001) but did not affect tracer-measured unidirectional lactate influx (nonstimulated: 235.4 +- 78.1; stimulated: 235.0 +- 31.0 nmol cntdot min-1 cntdot g-1. At a perfusate flow of 0.55 ml cntdot g-1 cntdot min-1 the unidirectional influx of 1 mM lactate was markedly inhibited (90 +- 5%) by 15 mM CIN. CIN also significantly reduced ovrhdot VO-2 from 6.2 +- 0.16 to 4.45 +- 0.57 ml cntdot kg-1 cntdot min-1 (P lt 0.05, n = 5). Phloretin (0.6 mM, n = 3) had no significant effect on lactate influx. Varying perfusate pyruvate concentration from 5 to 50 mM inhibited tracer lactate influx equally effectively as similar concentrations of lactate; the affinity of the process seemed to be similar for both molecules. These results add further experimental evidence to suggest the presence of a lactate transporter in skeletal muscle membrane and provide additional information concerning the physiological characteristics of lactate transport in and out of muscle.