Differential Effect of HOE642 on Two Separate Monovalent Cation Transporters in the Human Red Cell Membrane

Abstract

Residual K⁺ fluxes in red blood cells can be stimulated in conditions of low ionic strength. Previous studies have identified both the non-selective, voltage-dependent cation (NSVDC) channel and the K⁺ (Na⁺)/H⁺ exchanger as candidate pathways mediating this effect, although it is possible that these pathways represent different modes of operation of a single system. In the present study the effects of HOE642, recently characterised as an inhibitor of the K⁺(Na⁺)/H⁺ exchanger, on NSVDC has been determined to clarify this question. Radioisotope flux measurements and conductance determinations showed that HOE642 exerted differential effects on the NSVDC channel and the K⁺(Na⁺)/H⁺ exchanger, confirming that the salt loss observed in low ionic strength solutions represents contributions from at least two independent ion transport pathways. The findings are discussed in the context of red blood cell apoptosis (eryptosis) and disease.

Transmembrane Potential of Red Blood Cells Under Low Ionic Strength Conditions

“…This is in agreement with earlier findings assuming the absence of the K + (Na + )/H + exchanger in the membrane of bovine RBCs [16]. It was shown that the decrease of the intracellular pH of bovine RBCs in LIS solution after the maximum is reached declines significantly lower compared to human RBCs [16].…”

“…Donlon and Rothstein [6] decreased the extracellular ionic strength to a very low level and described the increase of the net K + loss as a triphasic response (curve with two inflection points). Starting at physiological ionic strength and reducing it, the K + (Na + )/H + exchanger is exclusively of importance to make a substantial contribution to the increase of the K + loss, at lower ionic strengths the NSVDC channel is additionally of importance, and at very low ionic strengths it seems reasonable to propose the start of an electrical break-down of the membrane [16]. …”

“…an enhanced K + efflux in sucrose media [18]. In addition, it was shown that the change of the intracellular pH of bovine RBCs in LIS solution after the maximum is reached declines significantly lower compared to human RBCs [16]. Demonstrating the time course of the membrane potential changes is essential for understanding the relative contributions of discrete transporters to transmembrane cation transport in this condition, and will allow the relative importance of the K + (Na + )/H + exchanger (probably the NHE7 isoform), classically associated with intracellular organelles, to be established.…”

Dynamic adhesion of eryptotic erythrocytes to endothelial cells via CXCL16/SR-PSOX

“…Eryptosis may result from activation of Ca 2ϩ -permeable cation channels with subsequent increase of cytosolic Ca 2ϩ concentration (5,6,17,18,25,27,28,33,48). The increase of cytosolic Ca 2ϩ is followed by cell shrinkage due to activation of Ca 2ϩ -sensitive K ϩ channels (12,14) and subsequent exit of KCl with osmotically obliged water (36).…”

Dimethyl sulfoxide at high concentrations inhibits non-selective cation channels in human erythrocytes

“…The most recent data (Kucherenko et al, 2012) have shown a blocking effect of furosemide on non-selective cation channel activity in human erythrocytes. Noteworthy, a chemical blocker HOE642 inhibited (up to 40%) cation leak current in human erythrocytes in isotonic NaCl bath solution in radiotracer experiments (Bernhardt et al 2007). It suggests that cation channels could be not only activated by toxins or chemical treatment (Tosteson et al 1991;Qadri et al 2011) but they have basal activity in untreated human erythrocytes.…”