Norepinephrine-stimulated PI hydrolysis in oligodendrocytes is mediated by alpha 1A-adrenoceptors

Oligodendrocyte progenitors were labelled with [3H]-myo-inositol in order to determine the effect of adrenergic agents on the accumulation of [3H]-inositol phosphates (InsP). Both norepinephrine and phenylephrine, a selective alpha 1-adrenoceptor agonist, increased the formation of [3H]-InsP, while isoproterenol, a beta-adrenoceptor agonist, did not. Propranolol (beta) and yohimbine (alpha 2), two adrenoceptor antagonists, had no significant effect on the NE-stimulated [3H]-InsP formation. By contrast, the response to NE was significantly blocked by phenoxybenzamine and the alpha 1-receptor antagonist, prazosin. Pretreatment with chloroethylclonidine, which selectively inactivates alpha 1B receptors, had no effect on NE-induced [3H]-InsP formation, while WB4101 had high potency in inhibiting this response. Pertussis toxin, which inactivates certain G-proteins, caused a approximately 60% reduction. NE-stimulated formation of [3H]-InsP depended on extracellular calcium influx, because it was decreased by 55% and 75% by chelation with EGTA or the addition of 1 mM CdCl2, respectively. These results suggest that oligodendrocyte progenitors express alpha 1-adrenoceptors characteristic of the alpha 1A subtype.