Norepinephrine-evoked calcium transients in cultured cerebral type 1 astroglia

We have used the CA++ indicator dye fura-2 AM and computerized imaging systems to investigate adrenergic regulation of intracellular calcium in cultured cerebral type 1 astroglia. We have found that norepinephrine (NE) and other adrenergic agonists stimulate increases in intracellular calcium in over 80% of type 1 astroglia tested. A wide range in effective NE concentrations was seen. With sufficient agonist concentrations the calcium response was biphasic, exhibiting an initial sharp peak followed by a sustained calcium elevation. This secondary component was sensitive to reductions in extracellular calcium concentrations and dependent on the continued presence of agonist. Pharmacological studies indicated that astroglial calcium responses were mediated by alpha 1- and alpha 2-adrenergic receptors. At times these two receptor subtypes appeared to underlie calcium responses by the same cells, whereas other cells only responded to stimulation of one or the other subtypes of alpha-adrenergic receptor. Finally, we have also observed spontaneous and agonist-evoked oscillations in astroglial calcium levels. The major findings of these studies indicate that 1) astroglial cells respond to alpha-adrenergic receptor stimulation with increased intracellular calcium, 2) these responses can be mediated by alpha 1-and/or alpha 2-adrenergic receptors, and 3) subpopulations of cerebral type 1 astroglia exist with respect to alpha-adrenergic receptor expression.