AJP - Cell Physiology, Vol 262, Issue 6 C1485-C1490, Copyright © 1992 by American Physiological Society
Kinetics of L-glutamate influx in single barnacle muscle fibers under 0-trans conditions
L. W. Horn
Department of Physiology, Temple University Health Science Center, Philadelphia, Pennsylvania 19140.
The dependence of L-glutamate influx on extracellular Na and L-glutamate
concentrations was determined using internally dialyzed single muscle
fibers of Balanus nubilus. Internal Na and glutamate concentrations were
held at zero, and the cell membrane potential was constant. Flux activation
curves for external glutamate were measured for five different external Na
concentrations, and flux activation curves for external Na were measured
independently for three different external glutamate concentrations. An
analysis of alternative kinetic models for the transporter mechanism was
made and led to the conclusions that under 0-trans conditions the
Na:glutamate stoichiometry is 1:1, that glutamate first binding to the
external transporter binding site is the preferred order under most
extracellular conditions, and that the Na:glutamate coupling is too tight
to permit measurable Na-independent glutamate uptake by the transporter.
