Na countertransport and cotransport in human red cells: function, dysfunction, and genes in essential hypertension

We describe in this paper studies on the modes of operation of ouabain-insensitive sodium transport systems in red cells of normotensive and hypertensive patients. We have extensively investigated the properties of Na countertransport and cotransport in order to clarify whether they are two different proteins or one transport protein with two modes of operation. Several criteria of discrimination between the two pathways are described: They differ in their affinity for Na and Li, sensitivity to several inhibitors, changes in cell volume, and chloride replacement by nitrate. We propose that there are two different transport systems. We have found elevated countertransport in red cells of hypertensive patients in France and in the United States. However, the cotransport system was found elevated in patients in Boston but reduced in patients in Paris. Studies of the modes of operation of the Na-K cotransport system indicate that it can promote K accumulation using an inward sodium gradient. This mode might be more efficient than Na extrusion at the physiological level of Na and K gradients. We interpret our findings of elevated Na-K cotransport in American hypertensive patients as an increased number of transport units functioning as K accumulators. It remains to be determined whether the reduced affinity for internal sodium of the outward cotransport is a defective outward cotransport or else a modulation of this transport system to favor K accumulation.