Relaxation of rat thoracic aorta induced by the Ca²⁺‐ATPase inhibitor, cyclopiazonic acid, possibly through nitric oxide formation

Abstract

1 The effect of the Ca2+-ATPase inhibitor, cyclopiazonic acid (CPA), was studied on rat thoracic aortic ring preparations. 2 At concentrations above 0.3 JM, CPA induced relaxation in the arteries precontracted with phenylephrine. Removal of the endothelium abolished CPA-induced relaxation.3 The nitric oxide (NO) synthase inhibitor NG-nitro L-arginine (3-300 AM), the free radical scavenger haemoglobin (O.1-33 AM), the soluble guanylate cyclase inhibitor, LY83583 (0.1-10 JAM), each inhibited the endothelium-dependent relaxation to CPA. The potassium channel blocker, glibenclamide (1O AM) and cyclo-oxygenase inhibitor, indomethacin (100 JAM for 60 min and then washed out) did not alter the action of CPA. 4 The calmodulin inhibitors calmidazolium (3-10 IAM) and W-7 (100 AM) also abolished CPA-induced relaxation.5 CPA (10 AM) increased guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels in arteries with an intact endothelium, without affecting adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 6 The inhibitors of NO synthesis and actions, the calmodulin inhibitor and removal of the endothelium abolished the CPA-stimulated increase in the levels of cyclic GMP. 7 In Ca2'-free solution, CPA failed to induce relaxation or to stimulate cyclic GMP production.Relaxation to nitroprusside was not affected under these conditions.

TRPC3 is involved in flow- and bradykinin-induced vasodilation in rat small mesenteric arteries1

“…In the rat aorta, it may promote Ca 2+ influx into endothelial cells to induce NO release from endothelial cells and then relax the aorta [18] . A different mechanism underlies the CPA-induced relaxation in mesenteric artery.…”

Sarcoplasmic-endoplasmic reticulum Ca2+-ATPase inhibition prevents endothelin A receptor antagonism in rat aorta

“…Depletion of agonist-sensitive Ca 2ϩ stores in either cell type results in elevation of cytosolic Ca 2ϩ concentration through SOC channels (SOCCs) (21). Elevation of Ca 2ϩ in endothelial cells activates endothelial nitric oxide synthase, yielding to endothelium-dependent vascular smooth muscle relaxation via nitric oxide (17,38,39). On the other hand, in the absence of intact endothelium, SOCCs also mediate Ca 2ϩ elevation in vascular smooth muscle (1,13,26,27,29,31,33).…”

Tyrosine Kinase May Participate in Ca2+ Entry for Endothelial Nitric Oxide Production

“…The endothelial NO synthase activity is dependent on cytoplasmic Ca 21 that has been suggested to be mostly derived from the extracellular space (1,2). Recent studies suggested that depletion of the Ca2+ store or endoplasmic reticulum (ER) could send an unidentified signal to the plasma membrane and allow the Ca 2+ to enter the cell in many types of non-excitable cells (3,4), including the endothelial cells in culture (5).…”

“…6) and thapsigargin, that could empty the Ca 21 in the ER without any known interaction with receptor-mediated cell signaling (3). More recently, the model has been shown to be applicable to intact endothelial cells and to have an important functional significance: the Ca 2+-ATPase inhibitors induced an endothelial NOmediated vasorelaxation that was exclusively dependent on the extracellular Ca 21 (2). In this study, we investigated the CPA-induced relaxation and cyclic GMP formation in the rat aorta to obtain a clue to delineate the Ca 2+ entry mechanism in endothelial cells, with a special reference to tyrosine kinase that has been recently shown to be intimately involved in a diversity of cellular functions (7), including cellular Ca2+-handling (8).…”

“…The Ca 21 ionophore was applied once to each ring in the absence or presence of methyl 2,5-dihydroxycinnamate since the effect of the relaxant was irreversible in nature. Cyclic GMP contents in tissues were determined by radioimmunoassay using a commercially available kit, as described previously (2).…”