The erythrocyte membrane in essential hypertension. Modified temperature-dependence of Li+ efflux

Elevated intracellular Ca2+ affects Lii-Nao countertransport in human red blood cells

Changes in cytoplasmic Ca2+ concentration and in Lii-Nao countertransport activity have been shown to be associated with essential hypertension. Elevated intracellular free [Ca2+], as well as abnormalities of Ca2+ binding and transport have been reported in cells from different tissues of hypertensive laboratory animals and essential hypertensive patients. Similarly, enhanced rates of Lii-Nao countertransport and the modified pattern of the temperature dependence of this activity in red blood cells from essential hypertensive patients have been previously demonstrated. The aim of the present study was to investigate possible interaction between changes in intracellular free [Ca2+] and the Lii-Nao exchange in human red blood cells. The ionophore ionomycin was used to allow Ca2+ incorporation into the cells in a dose-dependent manner. The elevation of intracellular [Ca2+], in turn, resulted in enhanced Li+ efflux from the cells. At 3 microM, ionomycin selectively and significantly enhanced the Lii-Nao countertransport but not Li+ leakage from the cells. EGTA totally abolished the effect of ionomycin, indicating that the effect is directly related to Ca2+. As low as 0.4 microM Ca2+ caused a statistically significant effect. The maximal effect of Ca2+ on the Lii-Nao countertransport was achieved around the external pH range of 6.8-7.5. In contrast, the leakage of Li+ was significantly enhanced by Ca2+ at a pH of 7.4 and above. Ca2+ did not affect the Km of the Lii-Nao countertransport for Li+. Amiloride, which inhibits Na+/H+ exchange, inhibited only 10% of the Ca2+-enhanced countertransport. It is concluded that Ca2+ may play a role in the regulation of Lii-Nao countertransport in erythrocytes.

Nuclear magnetic resonance investigation of human erythrocytes in the presence of manganese ions. Evidence for a thermal transition

Water proton transverse relaxation was investigated in whole blood and washed erythrocytes samples, respectively, at various temperatures and manganese concentrations. Water diffusional exchange controls proton relaxation in whole blood samples at higher Mn2+ concentrations (20-30 mM) or in washed erythrocyte samples at low Mn2+ content (1-5 mM). Mn2+ uptake is significant in washed normal erythrocyte samples when its concentration is about 18 mM or higher in the medium, at temperatures below about 26 degrees C. The thermal transition as revealed by the NMR doping method represents a switch from a water exchange process, mainly seen in the higher temperature range, to a paramagnetic ion controlled water proton relaxation in the lower temperature range.

Red cell sodium countertransport and cotransport in normotensive and hypertensive blacks

We have previously described elevated Lii -Nao countertransport (CT) and Na-K cotransport (CO) in red cells of Caucasian patients from Boston. In this study, we report both transport systems in black patients from Philadelphia. The maximal rate (Vmax) of CT was assayed by measuring the Nao-stimulated Li efflux from cells containing +/- 6 mmol Li/liter. The Vmax of outward cotransport was assayed by measuring the furosemide-sensitive component of Na and K efflux into Mg medium from cells containing 50 mmol/liter of both ions. The mean value of CT for 18 normotensive (NT) subjects with no family history of hypertension, (-) FHH , was 0.18 +/- 0.05 (mmol/liter cells X hour); and in 14 hypertensive (HT) patients, 0.18 +/- 0.07. The mean values of Na and K cotransport were, respectively (mmol/liter cells X hour), in 18 NT subjects with (-) FHH , 0.38 +/- 0.24 and 0.50 +/- 0.28 in 18 HT subjects, 0.25 +/- 0.17 and 0.24 +/- 0.14. We conclude that there is no difference in the Vmax for CT between the two groups of black subjects, but that the Vmax for Na-K CO was significantly reduced in the HT group. Notably, the offspring of HT patients (age 14 years, n = 17) also had a marked reduction in the Vmax of Na (0.15 +/- 0.17) K cotransport (0.19 +/- 14) in comparison with the mean value of Na (0.40 +/- 0.2) and K (0.60 +/- 0.3) cotransport measured in offspring (n = 10) of NT subjects (age 14 years).(ABSTRACT TRUNCATED AT 250 WORDS)

High-resolution 23Na-NMR studies of human erythrocytes: use of aqueous shift reagents

Aqueous shift reagents were used to clearly distinguish intra-and extracellular 23Na-nuclear magnetic resonance (NMR) signals in samples consisting of whole blood or suspensions of washed human erythrocytes (both fresh and outdated). The lanthanide chelates Dy(PPP)2(7-) and Tm( TTHA )3- were used to shift the extracellular signals upfield, and Dy( TTHA )3- and Tm(PPP)2(7-) were similarly used to shift extracellular resonances downfield. The absolute intensities of the signals were used along with the measured hematocrit to simultaneously determine the intra- and extracellular Na+ concentrations. The results were generally within 5% of the values determined by more time-consuming centrifugation-flame emission photometry measurements on the same samples. Thus the 23Na-NMR signals from both intra- and extracellular cations suffer no NMR invisibility within experimental error. The lower level of intracellular Na+ in fresh erythrocytes (less than 12 mM) is easily distinguished from the higher level (approximately 30 mM) in erythrocytes that have been stored (in the cold) outside the body for some weeks.

The erythrocyte membrane in essential hypertension. Characterization of the temperature dependence of lithium efflux

Erythrocytes of most patients with essential hypertension are distinguished by a typical pattern of temperature-dependence of Li efflux. In the present study we have attempted to characterize this unique temperature response. Measurements of Li efflux into Na medium and Lii-Nao countertransport were conducted simultaneously at finely spaced temperature intervals with increments of 1 to 2 degrees C in the range of 10-40 degrees C. The Arrhenius plots for the efflux in Na medium and for Lii-Nao countertransport in erythrocytes of both normotensives and hypertensives were biphasic with slopes representing apparent energies of activation of about 28 and 8 kcal/mol below and above the 'break', respectively. However, the 'break' in the Arrhenius plot appeared at distinctly different temperatures: 30 degrees C for normotensives and 20 degrees C for hypertensives. The Li efflux was resolved into N-ethylmaleimide-sensitive and -insensitive components. The sensitive component exhibited a typical biphasic temperature response, with the characteristic 'break': at 30 degrees C for normotensives and at 20 degrees C for hypertensives. In contrast, the N-ethylmaleimide-insensitive component was alike in normotensives and hypertensives. It is concluded that: (a) the unique temperature dependence of Li efflux in erythrocytes of hypertensives results from a localized modification in the membrane; (b) the N-ethylmaleimide-sensitive component represents a protein moiety which distinguishes between the erythrocyte membrane of normotensives and hypertensives; (c) the expression of the temperature dependence as judged by the sharp transition in slope (within 1 to 2 degrees C), apparently reflects the cooperative involvement of membrane lipids, associated with the Li efflux system.

Relationship between the intra-erythrocyte sodium composition and the membrane lipoprotein composition among different mammal species

Internal sodium and lipoprotein composition of RBCs of nine mammalian species are measured. A significant correlation can be demonstrated between the erythrocyte mean sodium value of studied species and the membrane protein/lipid ratio (r = 0.80, alpha less than 0.01). Erythrocyte internal sodium can be correlated with membrane-free cholesterol but not with the phospholipid fractions.

Temperature dependence and bidirectional cation fluxes in red blood cells from spontaneously hypertensive rats

The net passive influx of Na+ and efflux of K+ (orthodirection) through the red blood cell membranes from spontaneously hypertensive rats (SHR) were observed to be significantly higher (p less than 0.05) than those of three strains of normotensive rats when the measurements were made at 4 degrees C. Similar comparative studies, carried out at 37 degrees C, in the absence or presence of ouabain, showed no difference in these fluxes through this membrane from SHR compared to those from Wistar-Kyoto (WKY) rats, one of the normotensive strains. A study was undertaken to determine the temperature at which the greater cation fluxes in SHR red blood cells occurred. The net fluxes of Na+ and K+ decreased as the temperature was reduced from 37 degrees to 15 degrees C, but a paradoxical increase in the fluxes was observed as the temperature was decreased from 15 degrees to 4 degrees C. Only with this temperature shift (15 degrees to 4 degrees C) was the increase in flux significantly greater in SHR than in WKY cells. Subsequent studies were designed to determine whether the difference in the transport systems of red blood cells of SHR and WKY could be observed in fluxes of these cations in either direction across the membrane. For "reverse direction" flux studies, red blood cells were loaded with Na+ (to 130 mEq/liter cell water) and depleted of K+ (to 30 mEq/liter cell water) by incubation with the ionophore monensin.(ABSTRACT TRUNCATED AT 250 WORDS)

Essential hypertension: improved differentiation by the temperature dependence of Li efflux in erythrocytes

Kinetic and thermodynamic properties of red cell lithium (Li) efflux were examined in patients with essential hypertension; the maximal rate of Li efflux as affected by temperature was measured at the range of 12 degrees to 42 degrees C. Fifty-two patients with essential hypertension and 22 normotensives were studied. The mean Li efflux, both into sodium (Na) medium and Li-Na countertransport, was higher in hypertensive than in normotensive persons, but the distinction between the two groups was limited by extended scatter and overlap. The distinction could be markedly improved by determining the effect of temperature on Li efflux. While all the normotensives exhibited Arrhenius plots of Li efflux with a change in slope ("break") around 30 degrees C, the corresponding "break" for most (75%) of the hypertensives was about 20 degrees C. Consideration of both the rate and the temperature dependence of Li efflux further improved the differentiation of hypertensive patients. Analysis of normotensive offspring of hypertensives and of patients with secondary hypertension indicates that the temperature dependence of Li efflux may serve as a genetic marker for essential hypertension.

Intrinsic difference in erythrocyte membrane in spontaneously hypertensive rats characterized by Na+ and K+ fluxes

The goal of this study was to determine whether the elevated flux of sodium and potassium through the erythrocyte membrane of spontaneously hypertensive rats (SHR) is due to an intrinsic difference in the cell membrane or to a humoral factor present in the plasma. Isolated and washed erythrocytes from SHR and normotensive Wistar Kyoto (WKy) and Sprague-Dawley (SD) rats, were incubated in 1) a physiological salt solution, 2) WKy or SD plasma and 3) SHR plasma. Incubations were performed at 4 degrees C for 23 h. Erythrocytes from SHR incubated in physiological salt solution had significantly greater Na+ and K+ fluxes than those from normotensive WKy and SD rats (P less than 0.005). Plasma from any of the three strains of rats, as compared to physiological salt solution, increased Na+ influx in the following order: SD greater than WKy greater than SHR. Erythrocyte K+ efflux was not altered by plasma. We conclude that the elevated flux of Na+ and K+ in SHR erythrocytes is due to an intrinsic difference in the cell membrane. The greater Na+ influx in plasma from any strain of rats is not correlated with the blood pressure of the rat. The lesser increase in Na+ influx in erythrocytes incubated in plasma from SHR masks the greater intrinsic membrane permeability in the SHR erythrocyte when Na+ fluxes are studied in whole blood. The elevated flux of Na+ and K+ through the erythrocyte membrane of SHR may reflect a general membrane defect that underlies the pathogenesis of elevated arterial pressure.