Rat cerebral neurons matured in culture were stimulated with glutamate, and the effects of glutamate on the activities of the Na pump isoforms were investigated. Glutamate increased the total Na pump activity via a remarkable increase in the activity of the brain type (highly digitalis-sensitive) isoform and a slight decrease in the common type (weakly digitalis-sensitive) isoform activity. The effects of glutamate were produced in response to an enhancement of [Na+]i in the neurons, which resulted from passive Na+ influx through glutamate receptor-mediated cation channels. These results suggest that the Na pump isoforms in neurons differ in their physiological significance and that the brain type isoform plays an important role in restoring concentration gradients of Na+ and K+ after neuronal excitation.