Nitroprusside and cyclic GMP stimulate Na(+)-Ca2+ exchange activity in neuronal preparations and cultured rat astrocytes.

The effects of nitric oxide (NO)-generating agents on 45Ca2+ uptake in rat brain slices and cultured rat astrocytes were studied in the presence of monensin, which is considered to drive the Na(+)-Ca2+ exchanger in the reverse mode. Sodium nitroprusside (SNP) at > 10 microM increased monensin-stimulated Ca2+ uptake in the slices, although it did not affect high K(-)-stimulated Ca2+ uptake. Another NO donor, 3-morpholinosydnonimine, was effective. The effect of SNP was antagonized by hemoglobin (50 microM), a NO scavenger, and mimicked by 8-bromo-cyclic GMP (100 microM). In rat brain synaptosomes, SNP increased monensin-stimulated Ca2+ uptake, but it did not affect high K(+)-stimulated Ca2+ uptake. 8-Bromocyclic GMP, but not SNP, increased Na(+)-dependent Ca2+ uptake significantly in synaptic membrane vesicles in the absence of monensin. In cultured rat astrocytes, SNP and 8-bromo-cyclic GMP increased Ca2+ uptake in the presence of ouabain and monensin, which were required for the Ca2+ uptake in the cells. These findings suggest that NO stimulates the Na(+)-Ca2+ exchanger in neuronal preparations and astrocytes in a cyclic GMP-dependent mechanism.