Effect of endotoxic shock on kinetics of system A amino acid transport in rat soleus muscle

Michael Karlstad, M. M. Sayeed

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Abstract

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° C for 20, 40, or 60 min. Initial rates of entry of α-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 K(m) 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.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume251
Issue number1
StatePublished - Jan 1 1986

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Aminoisobutyric Acids
Amino Acid Transport Systems
Septic Shock
Skeletal Muscle
Muscles
Amino Acid Transport System A
Decapitation
Salmonella enteritidis
Inulin
Bicarbonates
Intravenous Injections
Buffers

All Science Journal Classification (ASJC) codes

  • Physiology
  • Physiology (medical)

Cite this

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title = "Effect of endotoxic shock on kinetics of system A amino acid transport in rat soleus muscle",
abstract = "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° C for 20, 40, or 60 min. Initial rates of entry of α-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 K(m) 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.",
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N2 - 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° C for 20, 40, or 60 min. Initial rates of entry of α-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 K(m) 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.

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