Enhanced erythrocyte Na+/H+ exchange predicts diabetic nephropathy in patients with IDDM.

Diabetic nephropathy develops in a subset of patients with an apparently hereditary predisposition. Microalbuminuria and elevated arterial pressure have been proposed as predictors of nephropathy but both appear when renal damage is impending. Enhanced sodium-hydrogen exchange in the cell membranes of diabetic patients is an early marker of diabetic nephropathy but its predictive value has not been assessed. In this study, sodium-hydrogen exchange was measured in erythrocytes as an initial velocity of amiloride-inhibited H+ efflux (pH 6.35-6.45) into a Na+ - containing medium (pH 7.95-8.05) in 156 non-microalbuminuric insulin-treated diabetic patients (98 women, 58 men, age 33+/-8 years, diabetes duration prior to enrollment 15+/-4 years) during 8 years of follow-up. Enhanced erythrocyte sodium-hydrogen exchange predicted diabetic nephropathy alone and in association with a familial tendency to hypertension/nephropathy with 86 and 96% sensitivity, and 80% specificity. Thus, sodium-hydrogen exchange appears to detect a subset of diabetic patients prone to develop renal damage, in whom a more intensive treatment modality might be considered.

Amiloride-sensitive Na+/H+ exchange in erythrocytes of patients with NIDDM: a prospective study.

Intensive treatment of non-insulin-dependent diabetes mellitus (NIDDM) decreases the rate of microvascular complications, but is associated with increased incidence of cardiovascular morbidity. Enhanced permeability of plasma membranes for sodium (e.g. sodium-hydrogen exchange, NHE) may predict the subset of diabetic patients for whom intensive modalities of treatment are indicated despite their potential risk. However, the accuracy of NHE as a marker of microangiopathy has not been assessed. In this study NHE as initial velocity of amiloride-inhibited H+ efflux from erythrocytes (pHi 6.35-6.45) into an Na(+)-containing medium (pHo 7.95-8.05), was estimated during 8 years of follow-up in 138 non-microalbuminuric diabetic patients (74 women, 64 men, age 52 +/- 4 years) treated with antihyperglycaemic drugs for 14 +/- 2 years. Appearance of microalbuminuria, overt proteinuria, azotaemia and retinopathy was assessed annually. Enhanced erythrocyte NHE predicted diabetic nephropathy alone and in association with a family history of hypertension and/or nephropathy with a sensitivity of 86 and 93%, respectively. No association was found between NHE and retinopathy in NIDDM. It is concluded that assessment of erythrocyte NHE can identify a subset of patients likely to develop renal damage, for whom an aggressive treatment approach might be considered.

Spironolactone prevents Na+/H+ exchange enhancement in primary aldosteronism.

The study was undertaken to determine the possible effect of an aldosterone antagonist, spironolactone (SP), on red blood cell sodium-hydrogen exchange (NHE) enhancement in primary aldosteronism (PA) and essential hypertension (EH). NHE was measured as the amiloride-inhibited fraction of H+ efflux (V max) from erythrocytes (pHi 6.40 +/- 0.05) into a Na+-containing medium (pHo 8.00 +/- 0.05). Subjects were 12 hypertensive patients with aldosterone-producing adrenal adenoma (six treated with 200 mg/day spironolactone for an least 5 days and six drug-free), 20 essential hypertensives (10 treated with the same regimen of spironolactone and 10 drug-free), and 20 healthy controls. Treatment with spironolactone decreased NHE in PA patients but did not change the mean NHE in essential hypertensives. It is concluded that SP may be useful to differentiate between elevated NHE in PA and essential hypertension.

Increased Na(+)-H+ exchange in red blood cells of patients with primary aldosteronism.

We measured Na(+)-H+ exchange as the amiloride-inhibited fraction of H+ efflux from red blood cells into a sodium-containing medium (pHo 7.95 to 8.05) at pHi values of 6.05 to 6.15, 6.35 to 6.45, 6.95 to 7.05, and 7.35 to 7.45 in 12 drug-free patients with primary aldosteronism before and after excision of histologically proven aldosterone-producing adrenal adenoma, 12 drug-free essential hypertensive patients, and 12 healthy control subjects. Red blood cell Na(+)-H+ exchange was increased in patients with primary aldosteronism similarly to the mean exchanger velocity in essential hypertensive patients compared with values in healthy subjects (334 +/- 25 and 310 +/- 29 versus 139 +/- 21 mumol H+/L cells per minute, respectively; P < .001 and .01). The kinetic parameters of Na(+)-H+ exchange returned to normal on day 2 after removal of the aldosterone-producing mass. Km for [Na+]o was not affected by aldosterone, whereas Km for [H+]i was decreased in patients with primary aldosteronism. The kinetic characteristics did not differ in essential hypertensive patients and control subjects. Protein kinase C inhibition in vitro by calphostin C (60 nmol/L) increased Km for [H+]i and caused up to a 65% suppression of Na(+)-H+ exchange (pHi 6.05 to 6.15). while diminishing Km for [Na+]o in red blood cells of patients with primary aldosteronism. The calmodulin antagonist W-13 (60 mmol/L) decreased exchanger velocity and increased Km for both H+ and Na+. We conclude that aldosterone stimulates red blood cell Na(+)-H+ exchange by a nongenomic mechanism that augments the exchanger affinity to Na+ and H+. In primary aldosteronism, protein kinase C and calmodulin seem to have synergistic stimulatory effects on red blood cell Na(+)-H+ exchange, and both increase the affinity of the exchanger to H+, while their effect on Na+ binding is opposite.

Na+-H+ exchange and other ion-transport systems in erythrocytes of essential hypertensives and spontaneously hypertensive rats: a comparative analysis.

The activity of ion-transport systems and Ca2+-induced erythrocyte haemolysis were compared between patients with essential hypertension and two strains of spontaneously hypertensive rats. Previous data on the increased rate of Na+-Li+ countertransport in erythrocytes of essential hypertensives were confirmed in this study. However, identification of Na+-Li+ countertransport in rat erythrocytes remained a complicated person because of the high rate of sodium-independent efflux of Li+. The rate of Na+-H+ exchange increased by 50-80% both in spontaneously hypertensive Wistar-Kyoto rats (SHR) and in patients with essential hypertension. No difference between Milan hypertensive strain rats (MHS) and Milan normotensive strain rats (MNS) was found. The rate of Na+,K+ cotransport increased in SHR and MHS erythrocytes compared with rats of the control strains [normotensive Wistar-Kyoto rats (WKY) and MNS; 30-50 and 90-110%, respectively]. No difference in this parameter was found between patients with essential hypertension and healthy subjects. Erythrocytes of patients with essential hypertension and of SHR were characterized by a higher sensitivity of their K+ channels to the increased concentration of intracellular Ca2+. This parameter did not change in MHS erythrocytes. Ca2+-induced haemolysis increased four- to fivefold in MHS erythrocytes compared with MNS and did not change in erythrocytes of SHR and patients with essential hypertension. The conclusion from these data is that the SHR strain is a more adequate model of human essential hypertension than the MHS.

Effect of protein kinase C activation on cytoskeleton and cation transport in human erythrocytes. Reproduction of some membrane abnormalities revealed in essential hypertension.

Certain manifestations of alterations of membrane cytoskeleton, protein kinase C activity, and ion transport were revealed in erythrocytes of patients with essential hypertension: 1) the average volume of erythrocytes is reduced by 4%; 2) about 7% of the total number of erythrocytes is represented by cup-shaped forms compared with 1.5 to 3.0% in the control group; 3) basal phosphorylation of Band 4.9 protein is increased 1.6-fold to 1.8-fold; 4) activity of protein kinase C is increased by 60 to 70%; 5) the rate of proton electrochemical gradient (delta mu H+)-induced Na+-H+ exchange is increased twofold. Treatment of erythrocytes of healthy donors with protein kinase C activator (12-O-tetradecanoylphorbol-13-acetate) leads to similar but more marked changes in cell shape (17% of cup-shaped forms), volume reduction (by 7%), an increase of Band 4.9 protein phosphorylation (threefold), and an increase in the rate of Na+-H+ exchange (fourfold). Protein kinase activation does not modify Na+-Li+ exchange and slightly increases (by 20-50%) Na+-K+ pump activity, Na+-K+ cotransport, and the rate of 45Ca influx. It may be assumed that the increase of protein kinase C activity is one of the most probable molecular mechanisms conditioning abnormalities of the membrane skeleton and Na+-H+ exchange in primary hypertension.

Evidence of lowered plasma membrane potential in different cell types in primary hypertension.

Basal electric potential in the plasma membrane of synaptosomes and platelets as well as the membrane potential in erythrocytes is lower in spontaneously hypertensive rats than in normotensive animals. Similar potential alterations have been found in platelets and erythrocytes of essential hypertensive patients. The reduction of the basal component of the transmembrane potential in synaptosomes and platelets in primary hypertension is partially or entirely compensated by an increase of its electrogenic component as a result of an enhanced activity of Na+K(+)-ATPase. In erythrocytes of patients with renal hypertension and in Cushing's syndrome no alterations of membrane potential are observed.