NHE1 knockout reduces blood pressure and arterial media/lumen ratio with no effect on resting pH_i in the vascular wall

Abstract

Key points• Small arteries are important for regulation of blood pressure and local blood flow.• Changes in intracellular pH alter artery tone although the mechanistic background has been unclear.• Using knockout mice for Na + /H + exchanger NHE1 with reduced acid extrusion from cells in the arterial wall and low intracellular pH in the absence of CO 2 /HCO 3 − , we show that intracellular acidification alters enzymatic activity and consequently artery dilatation and contraction.• Although lack of NHE1 does not affect intracellular pH in the arterial wall when CO 2 /HCO 3 − is present, arteries from NHE1 knockout mice have thinner walls and produce less active force due to reduced volume and cross-sectional area of individual smooth muscle cells.• These results highlight the interplay between intracellular pH and artery function, provide new targets to consider for modulating artery structure, and underscore the need to evaluate acid-base transport in conditions of vascular disease and blood pressure disturbances.Abstract Acid-base transport in the vascular wall remains incompletely understood. Here, we investigated (a) implications of Na + /H + exchanger NHE1 knockout for vascular smooth muscle (VSMC) and endothelial cell (EC) pH i regulation, mesenteric artery morphology, vasomotor function and blood pressure regulation, and (b) consequences of sustained EC and VSMC acidification for vasomotor function. Na + /H + exchange activity was abolished in VSMCs and ECs from NHE1 knockout mice, but with CO 2 /HCO 3 − present, steady-state pH i was unaffected. Active tension was 30% smaller in arteries from NHE1 knockout than wild-type mice, and media thickness equally reduced. Number of VSMCs per unit artery length was unchanged whereas volume and cross-sectional area of individual VSMCs were reduced. Media stress, force production per VSMC cross-sectional area and VSMC Ca 2+ responses were unaffected. Blood pressure was 25 mmHg lower in NHE1 knockout than wild-type mice. Omission of CO 2 /HCO 3 − caused VSMCs and ECs to acidify substantially more in NHE1 knockout (0.3-0.6 pH-units) than wild-type (0.02-0.1 pH units) mice. Removing CO 2 /HCO 3 − inhibited acetylcholine-induced NO-mediated relaxations in arteries from NHE1 knockout but not wild-type mice. Without CO 2 /HCO 3 − , effects of NO synthase and rho kinase inhibition on noradrenaline-induced contractions were smaller in arteries from NHE1 knockout than wild-type mice whereas the EC Ca 2+ response to acetylcholine, VSMC Ca 2+ response to noradrenaline and vasorelaxation to S-nitroso-N -acetylpenicillamine were unaffected. of VSMCs, reduced artery tension and lower blood pressure. At acidic pH i , NO-mediated vasorelaxation and rho kinase-dependent VSMC Ca 2+ sensitivity are reduced.

Splice Cassette II of Na+,HCO3− Cotransporter NBCn1 (slc4a7) Interacts with Calcineurin A

“…A potential role for calcineurin in artery remodeling is interesting in the context of acid-base transport because we and others have reported that NHE1 is important for artery structure development and remodeling (10,49,50). Further investigations are required to determine whether changes in NBCn1 activity induced by calcineurin inhibitors contribute to the observed effects on artery remodeling.…”

“…In the near physiological pH i range, NBCn1 is much more active than NHE1, and consequently, NBCn1 plays an important role for control of steady-state pH i (5,8,10). In congruence, knock-out of NBCn1 inhibits vasocontractile responses through a pH i -mediated decrease in rho-kinase-dependent VSMC Ca 2ϩ sensitivity (5).…”

“…In vascular smooth muscle cells (VSMCs) 3 of resistance arteries, acid extrusion during intracellular acidification is mostly Na ϩ -dependent and mediated by the Na ϩ ,HCO 3 Ϫ cotransporter NBCn1 (slc4a7) and the Na ϩ /H ϩ exchanger NHE1 (slc9a1) (5,(7)(8)(9)(10). In the near physiological pH i range, NBCn1 is much more active than NHE1, and consequently, NBCn1 plays an important role for control of steady-state pH i (5,8,10).…”

Extracellular ʜ ᴄ ᴏ3̅ is sensed by mouse cerebral arteries: Regulation of tone by receptor protein tyrosine phosphatase γ

“…Although a selective decrease in pCO 2 also has no effect on artery tone at pH o 7.1 (Figure 3d), a selective increase in pCO 2 lowers tension development (Figure 3d) with no effect on VSMC Ca 2þ dynamics (Figure 3e). The inhibitory effect of intracellular acidification on VSMC Ca 2þ sensitivity 5,12,18,26 likely contributes to the lower tension development observed at pH o 7.1 compared to 7.4 in the presence of low [HCO …”

Na+/H+ Exchange and Hypoxic Pulmonary Hypertension

“…Knockout of either the Na + /HCO 3 − cotransporter NBCn1, which alkalinizes cells by importing HCO 3 − , or NHE1 resulted in intracellular acidification in mouse vascular smooth muscle cells. 62,63 In both of these knockout animals, the smooth muscle in the resistance vessels of the systemic vasculature was marked by reduced norepinephrine-stimulated, ROCK-dependent Ca 2+ sensitivity. This suggests that ROCK activity may mediate changes in Ca 2+ sensitivity, and thereby vascular tone, in response to prolonged changes in pH i , but the extent to which the same mechanisms apply in the pulmonary vasculature remains unclear.…”