Endothelin-Induced Increases in Ca ²⁺ Entry Mechanisms of Vascular Contraction Are Enhanced During High-Salt Diet

Abstract

Abstract-High-salt diet is often associated with increases in arterial pressure, and a role for endothelin (ET)-1 in salt-sensitive hypertension has been suggested; however, the vascular mechanisms involved are unclear. We investigated whether ET increases the sensitivity of the mechanisms of vascular contraction to changes in dietary salt intake. Active stress and 45 Ca 2ϩ influx were measured in endothelium-denuded aortic strips of male Sprague-Dawley rats not treated or chronically infused intravenously with ET (5 pmol/kg per minute) and fed either normal-sodium diet (NS, 1%) or high-sodium diet (HS, 8%) for 9 days. Phenylephrine (Phe) caused increases in active stress that were similar in NS and HS, but were greater in NS/ET (maximum, 10.5Ϯ0.7) than in NS (maximum, 7.4Ϯ0.9) rats, and further enhanced in HS/ET (maximum, 14.4Ϯ1.1) compared with HS rats (maximum, 8.0Ϯ0.8ϫ10 4 N/m 2 ). Phe was more potent in causing contraction in NS/ET than in NS rats and in HS/ET than in HS rats. In Ca 2ϩ -free (2 mmol/L EGTA) Krebs, stimulation of intracellular Ca 2ϩ release by Phe (10 Ϫ5 mol/L) or caffeine (25 mmol/L) caused a transient contraction that was not significantly different in all groups of rats. In contrast, membrane depolarization by high-KCl solution, which stimulates Ca 2ϩ entry from the extracellular space, caused greater contraction in ET-infused rats, particularly those on HS diet. Phe (10 Ϫ5 mol/L) caused an increase in 45 Ca 2ϩ influx that was greater in NS/ET (27.9Ϯ1.7) than in NS (20.1Ϯ1.8) rats and further enhanced in HS/ET (35.2Ϯ1.8) compared with HS rats (21.8Ϯ1.9 mol/kg/min). The Phe-induced 45 Ca 2ϩ influx-stress relation was not different between NS and HS rats, but was enhanced in ET-infused rats particularly those on HS. The enhancement of the 45 Ca 2ϩ influx-active stress relation in ET-infused rats was not observed in vascular strips treated with the protein kinase C inhibitor GF109203X or calphostin C (10 Ϫ6 mol/L). Thus, low-dose infusion of ET, particularly during HS, is associated with increased vascular reactivity that involves Ca 2ϩ entry from the extracellular space, but not Ca 2ϩ release from the intracellular stores. The ET-induced enhancement of the Ca Key Words: arterial pressure Ⅲ endothelium Ⅲ vascular smooth muscle Ⅲ calcium Ⅲ contraction H igh-salt diet (HS) has been implicated in the pathogenesis of hypertension, particularly in salt-sensitive individuals, 1-4 and salt moderation is often recommended to protect against excessive increases in blood pressure. 1,2,5,6 Studies in salt-sensitive experimental animals such as the Dahl salt-sensitive rat have shown that HS is associated with significant increases in blood pressure. 7,8 Also, in saltsensitive rats, HS is associated with exaggerated vascular reactivity to vasoconstrictor stimuli, which may contribute, at least in part, to the increases in blood pressure. 9 -12 Although the mechanisms of salt-sensitive hypertension have not been clearly identified, several studies point to a possible role of endothelin (ET). 7,[13][14...

Effect of dietary sodium on vasoconstriction and eNOS-mediated vascular relaxation in caveolin-1-deficient mice

“…Our laboratory has previously shown that the effects of high dietary salt compared with normal salt on vascular function could be very subtle or undetectable in Sprague-Dawley rats (9,35). In contrast, our laboratory has documented that there are substantial differences in vascular function when animals on a normal or HS diet are compared with those on a sodium-restricted diet (40).…”

“…Our laboratory's previous studies in Sprague-Dawley rats have shown that changes in dietary salt alone are associated with slight or no change in BP or aortic vascular reactivity (9,35). The lack of salt sensitivity has been related to the possibility that the vasoconstrictive effects of HS are counterbalanced by HS-induced increase in NO production and vascular relaxation (9,35).…”

“…The lack of salt sensitivity has been related to the possibility that the vasoconstrictive effects of HS are counterbalanced by HS-induced increase in NO production and vascular relaxation (9,35). The association between changes in NO and sensitivity to sodium has been supported by studies showing salt sensitivity in rats or mice treated with L-NAME, which inhibits NOS (13,22,31) or with endothelin B receptor antagonist, which blocks endothelial endothelin B receptormediated NOS activation and NO production (9).…”

The Vascular Endothelin System in Hypertension - Recent Patents and Discoveries

“…Although some studies have shown that ET infusion in rats causes elevation of blood pressure [82], other studies have demonstrated that ET infusion causes slight or no change [56]. The difference in the results could be related to the activity of the ET batches from different commercial sources.…”

“…IP 3 acts on specific receptors on the intracellular Ca 2+ stores and stimulate Ca 2+ release [51]. ET also activates plasma membrane Ca 2+ channels and stimulates Ca 2+ influx from the extracellular space [55,56]. The ET-induced increase in diacylglycerol stimulates PKC activity [57][58][59].…”