hide
Free keywords:
Oocyte; Glutamate cotransport; Sodium ion dependence; Voltage clamp; (Xenopus)
Abstract:
The existence of an endogenous Na+-glutamate cotransporter in the oocytes of Xenopus laevis is demonstrated. The transporter does not accept D-glutamate as substrate. The dependence on substrate displays two saturating components with low (K1/2 = 9 mM) and high (K1/2 = 0.35 microM) affinities for L-glutamate. The dependence on external Na+ exhibits a saturating component with a K1/2 value of about 5 mM and a component that has not saturated up to 110 mM Na+. In voltage-clamped oocytes, it is possible to demonstrate that Na+-dependent L-glutamate transport is directly coupled to countertransport of Rb+. The analysis of the voltage dependence of the Na+,K+-dependent L-glutamate uptake suggests that positive charges are moved inwardly during the transport cycle.
