Stimulation of a Ouabain-Sensitive Rb+ uptake in human erthrocytes with an external electric field

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Abstract
(Na, K)ATPase of the red blood cell (RBC) is known to be electrogenic. Activation of this pump hyperpolarizes the RBC membrane by several millivolts. By exposing erythrocytes in an isotonic suspension to an alternating electric field it is possible to modulate transmembrane potential (δΩ) of the RBC. We have found that this modulation stimulates uptake of Rb+, against a chemical concentration gradient, when the applied AC field exceeds 10 V/cm (or an induced δΩ of 6 mV). The voltage-stimulated Rb+ uptake is completely inhibited by ouabain. Thus, (Na, K)ATPase may be involved. The stimulated Rb+ uptake is unrelated to the thermal effect by several lines of evidence. First, this uptake is above levels in controlled samples maintained at an identical temperature. Second, this uptake shows an optimum voltage. The maximum stimulation obtained in our experiment (26 amol/RBC·hr) occurs at 20 V/cm, i.e., a δΩ of 12 mV. Above or below this field strength the uptake is reduced. Third, this uptake is AC frequency depedent. It peaks around 1 kHz and diminishes at 1 MHz. The effective range is between 0.1 kHz to 0.1 MHz. A thermal effect would not be frequency dependent. In contrast to the ATP-dependent pumping activity of the (Na, K)ATPase, no stimulated Na+ efflux is detectable with the AC field. Neither Rb+ efflux, nor Na+ influx is stimulated by the AC field. Rb+ uptake is also stimulated by the AC field in a RBC sample treated with vanadate. The meaning of these observations is discussed.