Activation of EndothelinA Receptors in Frog Adrenocortical Cells Stimulates Both Calcium Mobilization from Intracellular Stores and Calcium Influx through L-Type Calcium Channels

Abstract

We have previously shown that endothelin (ET)-1 stimulates corticosterone and aldosterone secretion by the frog adrenal gland through activation of ETA receptors positively coupled to both the adenylyl cyclase and phospholipase C (PLC) pathways. The purpose of the present study was to investigate the involvement of calcium in ET-1-induced stimulation of corticosteroid secretion. Cytoautoradiographic labeling using [125I]ET-1 as a tracer revealed the presence of ET-1 binding sites on adrenocortical cells. Administration of graded concentrations of ET-1 in the vicinity of adrenocortical cells provoked a dose-dependent increase in cytosolic calcium concentrations ([Ca2+]i). ET-1 induced a biphasic response consisting of an immediate and transient peak of [Ca2+]i followed by a plateau phase. Preincubation of the cells with the calcium-ATPase inhibitor thapsigargin or the PLC inhibitor U-73122 reduced the amplitude of the transient phase. Administration of the calcium chelator EGTA or the protein kinase A inhibitor H-89 attenuated the plateau phase. The [Ca2+]i response to ET-1 was markedly reduced during concomitant administration of U-73122 and H-89. Preincubation of the cells with the L-type calcium channel blocker nifedipine attenuated the plateau phase. Corticosteroid secretion from perifused frog adrenal slices was almost completely suppressed by thapsigargin and reduced by nifedipine. Taken together, these data indicate that activation of ETA receptors in frog adrenocortical cells provokes immediate stimulation of PLC, which causes an early mobilization of calcium from intracellular stores, and activates adenylyl cyclase, which results in delayed calcium influx through L-type calcium channels. The resulting increase in [Ca2+]i plays a pivotal role in ET-1-induced corticosteroid secretion.

Production of NAADP and its role in Ca2+mobilization associated with lysosomes in coronary arterial myocytes

“…ET-1 is an important endothelium-derived vasoconstrictor. ET-1 exerts a wide spectrum of biological effects on smooth muscle cells via ET A and ET B receptors, including inhibition of voltage-gated K ϩ channels, activation of L-type Ca 2ϩ , as well as mobilization of intracellular Ca 2ϩ (4,17,20). Recent studies (34) have indicated that ET-1 exerts its Ca 2ϩ mobilizing action in pulmonary arteries through a lysosomeassociated Ca 2ϩ activation via NAADP.…”

Augmented Endothelin Vasoconstriction in Intermittent Hypoxia-Induced Hypertension

“…ET-1 increases [Ca 2ϩ ] i by efflux from the sarcoplasmic reticulum and by influx through membrane channels. 16,17,20,21 Furthermore, ET-1 can cause constriction by increasing calcium sensitivity via Rho kinase and protein kinase C activation, with subsequent inhibition of myosin light chain phosphatase. 18 This study indicates that ET-1 constriction of arteries from IH rats is independent of [Ca 2ϩ ] i changes.…”