Endothelial stimulation of sodium pump in cultured vascular smooth muscle

Vascular effects of the Mangifera indica L. extract (Vimang)

The effects of the Mangiferia indica L. (Vimang) extract, and mangiferin (a C-glucosylxanthone of Vimang) on the inducible isoforms of cyclooxygenase (cyclooxygenase-2) and nitric oxide synthase (iNOS) expression and on vasoconstrictor responses were investigated in vascular smooth muscle cells and mesenteric resistance arteries, respectively, from Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Vimang (0.5-0.1 mg/ml) and mangiferin (0.025 mg/ml) inhibited the interleukin-1beta (1 ng/ml)-induced iNOS expression more in SHR than in WKY, and cyclooxygenase-2 expression more in WKY than in SHR. Vimang (0.25-1 mg/ml) reduced noradrenaline (0.1-30 microM)- and U46619 (1 nM-30 microM)- but not KCl (15-70 mM)-induced contractions. Mangiferin (0.05 mg/ml) did not affect noradrenaline-induced contraction. In conclusion, the antiinflammatory action of Vimang would be related with the inhibition of iNOS and cyclooxygenase-2 expression, but not with its effect on vasoconstrictor responses. Alterations in the regulation of both enzymes in hypertension would explain the differences observed in the Vimang effect.

Estradiol-induced expression of N(+)-K(+)-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na(+)-K(+)-ATPase functions. We determined Na(+)-K(+)-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 +/- 11 vs. 367 +/- 29 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.01). Ovariectomy eliminated sex differences in Na(+)-K(+)-ATPase function, and chronic in vivo hormone replacement with 17beta-estradiol restored the ACh effect on Na(+)-K(+)-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na(+)-K(+)-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 +/- 7 vs. 197 +/- 12 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na(+)-K(+)-ATPase. Female-derived aortas exhibited a greater proportion of alpha2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of alpha2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1) NO-dependent increased Na(+)-K(+)-ATPase activity in female vascular tissue and 2) greater abundance of Na(+)-K(+)-ATPase alpha2-isoform in females.

ETA endothelin receptors are involved in the ouabain-induced haemodynamic effects in the periaqueductal gray area of rats

The aim of the present study was to asses the effects on blood pressure and vascular resistances elicited by microinjections of ouabain (OUA) within the periaqueductal gray area (PAG). We also tested whether peripheral vascular responses caused by exogenous intra-PAG ouabain involve activation of the PAG-endothelin system. In normotensive Sprague-Dawley rats the basal mean arterial blood pressure (MABP) was 114 +/- 3 mmHg. This was significantly increased by OUA (3 micro g, 122 +/- 2 mmHg, p < 0.05; and 6 micro g, 139 +/- 3 mmHg, p < 0.01) microinjected into the PAG area. Increases in MABP were associated with increases in total peripheral resistances (TPR), organ vascular resistances, and with reduced blood flow of almost all the organs tested: kidneys, skeletal muscle, skin, stomach, spleen, testes and intestine. Cardiac output did not change. Changes in the above vascular parameters induced by OUA were significantly (p < 0.01) reduced by intra-PAG microinjections of FR139317 (a selective ETA receptor antagonist, 5 nmol), SB209670 (a non-selective ETA/ETB receptor antagonist, 3 nmol), but not by BQ 788 (a selective ETB receptor antagonist, 5 nmol). In conclusion, OUA into the PAG area of normotensive rats caused significant changes in peripheral vascular parameters that are reduced by ETA receptor antagonists. These results indicate that PAG-ET-1 system via an action on ETA receptors is involved in the OUA effects.

Alterations in phenylephrine-induced contractions and the vascular expression of Na+,K+-ATPase in ouabain-induced hypertension

Hypertension development, phenylephrine-induced contraction and Na(+),K(+)-ATPase functional activity and protein expression in aorta (AO), tail (TA) and superior mesenteric (SMA) arteries from ouabain- (25 microg day(-1), s.c., 5 weeks) and vehicle-treated rats were evaluated. Ouabain treatment increased systolic blood pressure (127+/-1 vs 160+/-2 mmHg, n=24, 35; P<0.001) while the maximum response to phenylephrine was reduced (P<0.01) in AO (102.8+/-3.9 vs 67.1+/-10.1% of KCl response, n=12, 9) and SMA (82.5+/-7.5 vs 52.2+/-5.8%, n=12, 9). Endothelium removal potentiated the phenylephrine response to a greater extent in segments from ouabain-treated rats. Thus, differences of area under the concentration-response curves (dAUC) in endothelium-denuded and intact segments for control and ouabain-treated rats were, respectively: AO, 56.6+/-9.6 vs 198.3+/-18.3 (n=9, 7); SMA, 85.5+/-15.4 vs 165.4+/-24.8 (n=6, 6); TA, 13.0+/-6.1 vs 39.5+/-10.4% of the corresponding control AUC (n=6, 6); P<0.05. The relaxation to KCl (1 - 10 mM) was similar in segments from both groups. Compared to controls, the inhibition of 0.1 mM ouabain on KCl relaxation was greater in AO (dAUC: 64.8+/-4.6 vs 84.0+/-5.1%, n=11, 14; P<0.05), similar in SMA (dAUC: 39.1+/-3.9 vs 43.3+/-7.8%, n=6, 7; P>0.05) and smaller in TA (dAUC: 62.1+/-5.5 vs 41.4+/-8.2%, n=12, 13; P<0.05) in ouabain-treated rats. Protein expression of both alpha(1) and alpha(2) isoforms of Na(+),K(+)-ATPase was augmented in AO, unmodified in SMA and reduced in TA from ouabain-treated rats. These results suggest that chronic administration of ouabain induces hypertension and regional vascular alterations, the latter possibly as a consequence of the hypertension.

Cell volume and ionic transport systems after cold preservation of coronary endothelial cells

BACKGROUND

Hypothermia-induced changes in cell volume and ionic transport systems of coronary endothelial cells may play a role in the development of coronary artery disease in cardiac transplant recipients.

METHODS

Coronary endothelial cells were incubated in University of Wisconsin solution or culture control medium for up to 48 hours at 4 degrees C. Parallel control cultures were incubated at 37 degrees C. Na/K-ATPase and Na/K/Cl cotransport activities were determined as ouabain- and furosemide-sensitive 86Rb+ uptake, respectively. Cell volume changes and cell death were analyzed by a FACScan flow cytometer and the release of lactate dehydrogenase, respectively.

RESULTS

Coronary endothelial cells stored in University of Wisconsin solution up to 6 hours showed an increased Na/K-ATPase activity compared to control cells, whereas no changes were observed in Na/K/Cl cotransport activity or cell volume. Long-term preservation (24 and 48 hours) was associated with a partial loss of cell viability, as demonstrated by lactate dehydrogenase release, and dramatic alterations in ionic transport system activities.

CONCLUSIONS

University of Wisconsin solution seems to prevent coronary endothelial cells Na/K/Cl cotransport activity changes during cold preservation, which could alter cell volume regulation and cause cell injury.

Nitric oxide synthase induction by ouabain in vascular smooth muscle cells from normotensive and hypertensive rats

OBJECTIVE

To investigate the effect of ouabain on inducible nitric oxide synthase (iNOS) activity and expression in cytokine-stimulated vascular smooth muscle cells (VSMC) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

METHODS

VSMC were treated for 24 h and afterwards, nitric oxide (NO) release was determined by the production of nitrite, a stable metabolite of NO. Activity of iNOS was measured by the conversion of [3H]-L-arginine to [3H]-L-citrulline and iNOS protein expression by Western blotting.

RESULTS

Ouabain (0.01-1 mmol/l) further enhanced interleukin-1beta (II-1beta)-induced nitrite production by WKY and SHR VSMC, although a more pronounced effect was observed in SHR cells (maximum response 52.1 +/- 5.2 and 71.2 +/- 6.4% of 11-1beta effect in WKY and SHR cells, respectively). Such response on NO release was mimicked by the calcium ionophore A 23187 (0.01-1 micromol/l) and abolished by the voltage-operated calcium channels (VOCC) nifedipine (0.1 micromol/l). Expression of iNOS showed that ouabain increased the synthesis of the enzyme in WKY and SHR VSMC stimulated with II-1beta, and this effect was higher in SHR cells. The increased iNOS expression was significantly reduced by nifedipine.

CONCLUSIONS

Ouabain stimulation of iNOS expression and activity in II-1beta-stimulated VSMCs from WKY rats and SHR seems to be related to increased intracellular calcium influx through VOCC. The more pronounced effect observed in SHR VSMC could be explained by an altered calcium entry in the hypertensive strain.

Angiotensin II mediates cell hypertrophy in vascular smooth muscle cultures from hypertensive Ren-2 transgenic rats by an amiloride- and furosemide-sensitive mechanism

We have reported that cultured vascular smooth muscle cells (VSMC) from hypertensive Ren-2 transgenic rats (TGR) are constitutively hypertrophic when compared to matched cells from normotensive Sprague-Dawley rats (SD), by a mechanism involving the endogenous production of angiotensin II (AII). In the present work, we analyzed the possible involvement of two Na+ transport mechanisms in TGR-VSMC hypertrophy. In both SD- and TGR-VSMC, AII increased both cell size, by a furosemide- and amiloride-sensitive mechanism, and Na+/K+/2Cl- cotransport activity, by an amiloride-sensitive mechanism. Under basal unstimulated conditions, TGR-VSMC showed higher cell size and Na+/K+/2Cl- cotransport activity than SD-VSMC. Under these same conditions, losartan, furosemide, or amiloride reduced cell size only in TGR-VSMC. Similarly, basal cotransport activity was reduced by losartan and amiloride to levels similar to those observed in SD-VSMC. We conclude that hypertrophy of TGR-VSMC is dependent on the endogenous production of AII and mediated by increased Na(+)-H+ exchange and Na+/K+/2Cl- cotransport activities.