Lactate and metabolic h+ transport and distribution after exercise
across white muscle cell membranes in rainbow trout: a perfusion
study .
Wang, Yuxiang, George J. F. Heigenhauser, and Chris M. Wood.
Department of Biology and Department of Medicine, McMaster
University, Hamilton, Ontario, Canada
APStracts 3:0171R, 1996.
An isolated-perfused tail-trunk preparation was employed to study the
influence of transmembrane pH gradient and membrane potential (Em) on
the transport and distribution of L(+)-lactate (Lac), metabolic H+
(_Hm+), and related parameters in rainbow trout white muscle after
exhaustive exercise. One resting (pHa nearly equal to 7.9) and four
post-exercise treatments (pHa nearly equal to 7.4, 7.9, 8.4, and
high-K+, pHa nearly equal to 7.9, partially depolarized by 15 mM K+)
were examined. Variations in HCO3- concentration (2-18 mM) at
constant Pco2 nearly equal to 2 torr were used to alter pHa. The
elevated intracellular Lac ( nearly equal to 50 mM) remained
unchanged after 60 min of perfusion due to very low rates of lactate
efflux and oxidation. H+, HCO3-, and Lac- distributions were all well
out of electrochemical equilibrium. Total CO2 efflux was reduced at
high extracellular pH; alterations in the net driving force on HCO3-
may have overshadowed the influence of Pco2 gradients in driving
total CO2 efflux. Lac efflux and _Hm+ flux were completely uncoupled.
_Hm+ flux reacted to both acid-base and electrochemical gradients as
_Hm+ efflux dropped and even reversed when pHe decreased, while
partial depolarization in conjunction with depressed intracellular pH
(pHi) resulted in elevated _Hm+ efflux. Lac efflux did not respond to
changes in pHe. Changes in Lac efflux corresponded more closely to
changes in the Lac- concentration gradient than in the HLac gradient.
This study provides circumstantial evidence for the involvement of
electroneutral mechanisms (i.e. Lac-/H+ co-transport and/or Lac
-/anion exchange) in lactate efflux, but does not eliminate the
possibility of an active transport mechanism contributing to the
retention of Lac.
Received 5 December 1995; accepted in final form 23 April 1996.
APS Manuscript Number R766-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96