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.

Enhanced red cell sodium-hydrogen exchange in microvascular angina.

OBJECTIVES: Enhanced calcium content in arterial smooth muscle cells and altered reactivity of coronary vessels to alkalinization have been reported in angina pectoris due to impaired motility of coronary arteries. An altered function of sodium-hydrogen exchange, a ubiquitous membrane transport system that links proton efflux to calcium drifts, may mediate these phenomena. DESIGN AND SUBJECTS: Twenty patients with microvascular angina (stable effort angina, reversible perfusion defects during effort thallium 201 heart scintigraphy, and angiographically normal coronary arteries) were compared to 20 patients with stable effort angina due to coronary atherosclerosis and 20 healthy subjects. The sodium-hydrogen exchange was defined as the initial fraction of the amiloride-sensitive proton efflux from red cells with inhibited anion exchanger (pHi 6.00-6.05) into an Na(+)-containing medium (pHo 8.00-8.05). 12-0-tetradecanoylphorbol-13-acetate (TPA, 600 nmol.l-1) and staurosporine (100 nmol.l-1) were used as phosphorylation modulators in vitro. RESULTS: The mean red blood cell Na+/H+ exchange was increased in patients with microvascular angina (451 +/- 37 vs 142 +/- 17 and 124 +/- 21 umol H+.1 cells-1.min-1, P < 0.01). TPA and staurosporine abolished differences between the groups. CONCLUSIONS: Microvascular angina is associated with enhanced Na+/H+ exchange in erythrocytes, probably due to more extensive phosphorylation of the membrane antiporter sites.

[Red cell Na+/H+ exchange and role of protein kinase C in its stimulation in diabetes mellitus, essential hypertension and nephropathy].

Na+/H+ exchange (NHE) was measured as maximal initial velocity of pH-dependent H+ efflux from red cells into an alkaline medium containing Na+ in patients with insulin-dependent or noninsulin-dependent diabetes, with and without hypertension and in normoglycemic, essential hypertensives and normal controls (50 subjects in each subgroup). Maximal velocities of NHE were found in microalbuminuric patients in all subgroups, and NHE correlated with the rate of micro-albuminuria (r = 0.61, p = 0.02). Daily insulin requirements were greater in those with elevated NHE (84 +/- 8 vs 42 +/- 4 U/day). There was no correlation between NHE and levels of plasma glucose, HbA1 and plasma aldosterone and lipid profile and PRA. NHE was correlated with plasma prolactin (r = 0.51, p = 0.02) and PTH r = 0.24, p = 0.05). In uremic patients, NHE was inversely correlated with creatinine clearance (r = -0.48, p = 0.03). Since calphostin C, a selective inhibitor of protein kinase C, lowered increased NHE in vitro, the protein kinase C-dependent pathway of the exchanger regulation was concluded to be responsible for NHE activation in diabetes mellitus and essential hypertension.

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.

Common variable immunodeficiency associated with myelocathexis and altered membrane sodium-proton antiport.

Alterations in protein kinase C (PKC) activity have been implied in the pathogenesis of common variable immunodeficiency (CVID). We analyzed amiloride-sensitive red blood cell Na+/H+ exchange (sodium-proton antiport, SPA) and its response to protein kinase stimulation in a patient with CVID. Compared with healthy subjects or patients with sepsis, a unique pattern of SPA activation has been shown. The patient's SPA was decreased and unresponsive to PKC stimulation, whereas stimulation by insulin, a tyrosine kinase activator, restored SPA activity. An alteration of serine-threonine phosphorylation is suggested as a possible mechanism for the immune failure.

Red cell Na+/H+ exchange and B cell alloantigen 883 (D8/17) in patients with acute rheumatic fever and inactive rheumatic heart disease.

The association of Na+/H+ antiport with 883 alloantigen was studied in patients with rheumatic disease. Simultaneous measurements were made of red cell Na+/H+ exchange and 883 alloantigen in microlymphocytotoxic test with D8/17 monoclonal antibodies in 20 patients with acute rheumatic fever, 20 patients with inactive rheumatic heart disease, 20 patients with atherosclerotic heart disease (stable anginal syndrome), and 20 healthy subjects. The number of 883(+) B cells and the Na+/H+ antiport activity were increased in rheumatic fever compared to healthy controls: 24.8 +/- 0.4 vs. 11.1 +/- 1.0% cells, 431 +/- 43 vs 121 +/- 12 micromol H+/l cells in min, respectively; p < 0.001; and in patients with rheumatic heart disease compared to patients with atherosclerotic heart disease; 25.7 +/- 1.8 vs. 9.8 +/- 1.1% cells, 482 +/- 73 vs. 124 +/- 12 micromol H+/l cells in min, respectively; p < 0.001.