Abstract

The effects of catecholamines on intracellular Ca2+ concentrations ([Ca2+](i)) in single acutely dissociated bovine adrenal medulla endothelial cells (BAMECs) were measured using the intracellular fluorescent probe Fluo-3 AM. 100 mu m epinephrine or norepinephrine induced a biphasic [Ca2+](i) rise with an initial peak followed by a delayed phase. 10 mu m phenylephrine (alpha(1)-adrenergic agonist) caused a [Ca2+](i) rise similar to that evoked by catecholamines. The increase in [Ca2+](i) induced by 10 mu m phenylephrine was reverted by 10 mu m phenoxybenzamine (alpha-adrenergic antagonist). Neither isoproterenol (beta-adrenergic agonist) nor clonidine (alpha(2)-adrenergic agonist) induced [Ca2+](i) rise. The initial peak was insensitive to zero external Ca2+ and it was abolished after Ca2+ internal storages were emptied by 10 mM caffeine. The delayed phase was reduced to near zero by external Ca2+ removal. These results indicate that BAMECs possess alpha(1)-adrenergic receptors associated to both the release of caffeine-sensitive intracellular Ca2+ stores and the entry of extracellular Ca2+ We suggest that chromaffin cell secretion may activate BAMECs in vivo through an increase in [Ca2+](i) which could induce the secretion of vasoactive factors allowing a rapid entry of hormones into the circulation.