HIV‐1 gp120 Glycoprotein Induces [Ca2+]i Responses not only in Type‐2 but also Type‐1 Astrocytes and Oligodendrocytes of the Rat Cerebellum

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Abstract
Cultures of cerebellar cortex cells were exposed to the HIV-1 envelope glycoprotein, gp120, and investigated for cytosolic Ca2+ ion concentration ([Ca2+]i) changes by the fura-2 ratio videoimaging technique while bathed in complete, Na(+)-free or Mg(2+)-free Krebs-Ringer media. At the end of the [Ca2+]i experiments the cells were fixed and immunoidentified through the revelation of markers specific for neurons (microtubule associated protein-2), type-2 (A2B5) or all (glial fibrillary acidic protein) astrocytes, oligodendrocytes (galactocerebroside) or microglia (F4/80 antibody). In complete medium, rapid biphasic (spike-plateau) responses induced by gp120 (0.1-1 nM) were observed in a subpopulation of type-2 astrocytes. In addition, slow but progressive responses were observed in other type-2 cells and oligodendrocytes, whereas type-1 astrocytes showed small responses, if any, and granule neurons did not respond at all. Use of Na(+)-free medium (a condition that blocked another gp120-induced response, cytosolic alkalinization) resulted in an increase in [Ca2+]i response that was appreciable not only in type-2 but also in most type-1 astrocytes, possibly because of the inhibition of the Na+/Ca2+ exchanger and the ensuing decrease in Ca2+ extrusion. Granule neurons, including those in direct contact with responsive astrocytes, remained unresponsive, even when the experiments were carried out in Mg(2+)-free medium supplemented with glycine, a condition that favors activation of the glutamatergic N-methyl-D-aspartate (NMDA) receptor.(ABSTRACT TRUNCATED AT 250 WORDS)