AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 1 150-R156, Copyright © 1986 by American Physiological Society
Effect of endotoxic shock on kinetics of system A amino acid transport in rat soleus muscle
M. D. Karlstad and M. M. Sayeed
This study evaluated the kinetics of system A amino acid transport in
soleus muscle during endotoxic shock. Fasted male rats (80-100 g) were
killed by decapitation 5 h after the intravenous injection of saline
(control) or 20 mg/kg Salmonella enteritidis endotoxin. Soleus muscles (40
mg) from control or endotoxic rats were incubated in oxygenated
Krebs-Ringer-bicarbonate buffer (pH 7.4) at 37 degrees C for 20, 40, or 60
min. Initial rates of entry of alpha-aminoisobutyric acid (AIB) into the
inulin-inaccessible space of muscles were measured over a wide range of AIB
concentrations (0.1-20.0 mM). Initial rates of AIB transport were separated
into two parallel transport processes, a saturable carrier-mediated
component and a nonsaturable passive diffusive process. The diffusion
constant for the nonsaturable process in the endotoxic muscles (0.36 h-1)
was 38% greater than control muscles (0.26 h-1). The maximum rate of AIB
transport decreased from 55.6 +/- 3.3 nmol . g dry wt-1 . min-1 in controls
to 18.3 +/- 1.9 nmol . g dry wt-1 . min-1 in endotoxic muscles. The
apparent Km for saturable AIB transport was not different between control
(1.68 +/- 0.12 mM) and endotoxic muscles (1.64 +/- 0.19 mM). Alterations of
system A amino acid transport in endotoxic soleus muscles were due to an
increase in passive AIB diffusion and a decrease in the number and/or
activity of existing carriers and not to a change in carrier affinity for
AIB. These results elucidate the mechanism for the decreased amino acid
transport (system A) by soleus muscle in endotoxic shock.
