CALCIUM-DEPENDENT NITRIC-OXIDE FORMATION IN GLIAL-CELLS

We have previously demonstrated nitric oxide (NO)-dependent cyclic GMP (cGMP) formation in response to noradrenaline (NA) and glutamate (GLU ) in astrocyte-enriched cultures from rat cerebrum. In the present wor k we show heterogeneity in agonist responses in astrocyte cultures fro m cerebellum, hippocampus and cortex. The response to NA was higher in cells from cerebellum, intermediate in cultures from hippocampus and low in cortical astrocytes. GLU had no significant effect in cortical and cerebellar cultures and presented lower effects than NA in cells f rom hippocampus. The NO donor sodium nitroprusside (SNP produced much higher cGMP levels than agonists and the order of efficacies was cereb ellum > cortex > hippocampus. Responses to NA and SNP in cerebellar as trocytes were sensitive to culture conditions decreasing when cells we re seeded at low density or subcultured. Microglial cells were the mai n contaminants of the cerebellar astrocyte cultures but did not contri bute to the NA or the SNP responses. No soluble guanylyl cyclase or ca lcium-dependent NO synthase (cNOS) activities were detected in microgl ial cultures. The effect of NA in cerebellar astrocytes was blocked by L-arginine analogues and by the alpha(1)-adrenoceptor antagonist praz osin. The calcium ionophore A23187 mimicked the effect of NA and omiss ion of calcium from the medium prevented both responses. NA did not el icit cGMP formation in granule cell cultures. These results support an astroglial location of the alpha(1)-adrenoceptors and the cNOS that m ediate NA stimulation of cGMP formation in cerebellum.