Transport kinetics for the uptake of (3H)glycine and (3H)L-glutamate into dorsal and ventral slices of rat spinal cord.

The uptake of [3H]glycine and [3H]L-glutamate into slices of the dorsal and ventral halves of rat spinal cord taken from the thoracal (T3-9) and lumbar (L1-6) regions was determined in the concentration range 2 - 1 000muM. For both amino acids and in all four tissue pieces (thoracal dorsal and ventral, lumbar dorsal and ventral) biphasic linear regressions were obtained from the Lineweaver-Burk plots, demonstrating saturable transport mechanisms both in the high-affinity and in the low-affinity range. No significant dorsal-ventral or lumbar-thoracal differences were found for the transport constants Km of both amino acids. For the maximum velocity V similar dorsal-ventral and lumbar-thoracal gradients were found for both glycine and L-glutamate. These results, which are not entirely in agreement with the distribution of the endogenous pools of these amino acids, are critically discussed in view of the proposed function of high affinity uptake at the synapse.