Activation of calcium mobilization and calcium influx by alpha 1-adrenergic receptors in a smooth muscle cell line

Abstract

Alpha 1-adrenergic receptor (α 1R) mediated increases in the cytosolic levels of free Ca +2 and the inositol phosphates were measured in a smooth muscle cell line, DDT 1. Norepinephrine (NE) stimulated a rapid increase in cytosolic Ca +2 by two distinct components: 1) release of Ca +2 from intracellular sites (mobilization), and 2) influx of extracellular Ca +2. The mobilization component was not affected by removal of extracellular Ca +2 or addition of La +3 or Co +2 to the buffer. The influx component was abolished by EGTA, La +3, or Co +2, but was not affected by the voltage-operated Ca +2 channel blockers diltiazem or nifedipine. Depolarization of DDT 1 cells with 100 mM KCl or with gramicidin did not induce Ca +2 influx. NE also increased inositol trisphosphate to 78% over basal levels within 1 minute. These results suggest that α 1R on DDT 1 cells are coupled to both the mobilization of intracellular Ca +2 and to receptor-operated Ca +2 channels in the plasma membrane, and that polyphosphoinositide hydrolysis may play a role in these phenomena.