pH‐dependent stimulation by Ca²⁺ of prostacyclin synthesis in rat aortic rings: effects of drugs and inorganic ions

Abstract

1 Fresh rat aortic rings were incubated in HEPES-buffered salt solutions. Extracellular Ca24 stimulated the production of prostacyclin (PGI2), as determined by radioimmunoassay of its stable hydrolysis product 6-oxo-prostaglandin F,. This action of Ca24 was modified by H4 over the pH range 8.0-6.5. Stimulation by calcium ionophore A23187 was not pH-dependent.2 In parallel incubations of aortic rings with 4 Ca2", followed by washing in the presence of La3, tissue uptake of 45Ca2" increased progressively as extracellular pH was increased from 6.5-8.0. Over this range intracellular pH, estimated by the distribution of ['4CJ-dimethadione, varied from 5.9-7.4.3 Stimulation by Ca24 of PGO2 synthesis was concentration-dependent over the range 0.7-20 mm. The maximum effect was an increase of approx. 4 fold. 4 Nifedipine, but not verapamil or diltiazem, inhibited Ca24-stimulated PGI2 synthesis. A dihydropyridine compound that activates voltage-dependent Ca24 channels, Bay K 8644, did not increase PGI2 synthesis. 5 8-(N, N-diethylamino)-octyl-3,4,5 timethoxybenzoate (TMB-8), an antagonist of intracellular Ca24 mobilisation, inhibited basal and Ca24-stimulated PGO2 synthesis to a similar extent. 6 A solution containing 40 mM K4 reduced Ca24-stimulated PGI2 production. Mg24 stimulated PGI2 synthesis in a pH-dependent manner but was less potent than Ca2 . Other divalent cations (Mn24, Ba24 and Sr`9), and La34 had little or no effect on basal or Ca2+-stimulated PGI2 synthesis.

Effects of acid-base imbalance on vascular reactivity

“…In contrast to piglet pulmonary vessels, NO did not contribute to alkalosisinduced vasodilation in the rabbit (31) or rat (32) lung. PGI 2 synthesis, like NO synthesis, is enhanced by increased endothelial cell cytosolic Ca 2+ (33). These findings reflect the interspecies differences in dominant endothelium-derived modulator synthesis.…”

Alkalosis stimulates endothelial nitric oxide synthase in cultured human pulmonary arterial endothelial cells

“…Besides the NO story for the vasodilatory mechanism of alkalization, it has been demonstrated that alkalosis enhances prostacyclin synthesis (15,22,32). However, we could not detect augmentation of cyclooxygenase-1 mRNA and protein expression during alkalosis in our assay methods (unpublished observation).…”

Actions of amiloride analogues on prostacyclin synthesis by rat aortic rings

“…Aortic rings were prepared by methods similar to those described previously (Bunting et al, 1976;Ritter et al, 1987 HEPES were the same as in the other protocol. Amiloride and the analogues studied were prepared specially for this study by previously published methods (Cragoe et al, 1967;.…”

“…PGI2 synthesis is inhibited by 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB8) (Brotherton & Hoak, 1982;Ritter, 1984) an antagonist of intracellular Ca2" mobilisation (Malagodi & Chiou, 1974). In contrast, drugs that influence voltage-dependent Ca2+ channels have variable actions on PGI2 synthesis in different preparations and are often only effective at high concentration (Whorton et al, 1984;Jeremy et al, 1985;1986;Hassid & Oudinet, 1986;van de Velde et al, 1986;Mehta et al, 1986;Ritter et al, 1987). In rat aortic rings, stimulation ofPGI2 synthesis 'Author for correspondence.…”

“…by external Ca2l is pH-dependent (Taylor et al, 1986;Ritter et al, 1987), raising the possibility that Ca2ì nflux and/or intracellular Ca2" action is inhibited by H+.…”