Abstract
Ketamine, etomidate, propofol, and pentobarbital were compared for effects on and interactions with the type 1 facilitative glucose transporter (GLUT-1). Fluxes of radiolabeled hexoses were used to determine the effects of anesthetics on GLUT-1 function. Hypotonic hemolysis of human erythrocytes was used to assess perturbations of membrane integrity. Quenching of intrinsic protein fluorescence was used to assess the direct interactions of anesthetics with purified GLUT-1. Pentobarbital, ketamine, etomidate, and propofol inhibited glucose transport in murine fibroblasts with ic 50 values of 0.8, 1.6, 0.1, and 0.4 mM, respectively. Pentobarbital, ketamine, etomidate, and propofol also inhibited sugar transport in human erythrocytes. The ic 50 values for pentobarbital and ketamine exhibited substrate dependence for equilibrium exchange but not unidirectional effluxes. This was not observed for etomidate. Propofol did not inhibit equilibrium exchange but did inhibit unidirectional efflux with little substrate dependence. Pentobarbital protected against hemolysis, whereas etomidate and ketamine promoted hemolysis of erythrocytes. Propofol had no effect on membrane integrity. Pentobarbital, ketamine, and etomidate all interacted directly with GLUT-1, with apparent K d values of 2.2, 0.8, and 0.5 mM, respectively. Like barbiturates, ketamine, etomidate, and propofol inhibited GLUT-1 at concentrations near to those used pharmacologically. Inhibition of GLUT-1 by these intravenous general anesthetics was complex, exhibiting differential kinetic effects on equilibrium exchange versus unidirectional fluxes and contrasting substrate dependencies. Like barbiturates, ketamine and etomidate bound to GLUT-1 with affinities that paralleled inhibition of glucose transport. As a class, intravenous general anesthetics, in contrast to inhalation anesthetics, inhibit GLUT-1-mediated glucose transport.
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