Plasma membrane potential of Lettré cells does not depend on cation gradients but on pumps

Abstract

The plasma membrane potential of Lettré cells has been determined with the optical indicator oxonol-V and found to be -57 mV at 37 degrees C (range -20 to -80 mV depending on the physiological condition of the cells). Increasing extracellular K+ does not depolarize cells: even in the presence of 155 mM K+ the potential is -41 mV; membrane potential is also insensitive to the chemical gradient of Na+, Mg2+, Ca2+ or Cl-. Ouabain depolarizes the cells; H+ efflux from cells is stimulated by extracellular Na+. We propose that in Lettré cells the plasma membrane potential is generated by electrogenic cation pumps. The balancing fluxes of Na+ and K+ are mainly through electroneutral cation exchanges (Na+/K+ and Na+/H+) and the magnitude of the potential is limited by organic anion leaks. Such a mechanism may operate in other biological membranes also.

Transmembrane sodium and potassium gradients modulate histamine secretion induced by ionophore A23187

“…In our experiments the impairment of sodium and potassium gradients did not induce histamine release but facilitated the secretagogue-effect of antigen, compound 48/80 or ionophore A23 187. In contrast the inhibition of sodium-potassium ATPase in neuronal cells (Vizi et al, 1982) and in chromaffin cells (Pocock, 1983) (Bashford & Pasternak, 1984) indicated that electrogenic pump(s) can generate membrane potential. In these cells increasing extracellular KCI up to 80 mM did not modify membrane potential whereas ouabain depolarized the membrane.…”

The kinetics of transport of lactate and pyruvate into isolated cardiac myocytes from guinea pig. Kinetic evidence for the presence of a carrier distinct from that in erythrocytes and hepatocytes

“…These discrepancies, which are greater at high lactate concentrations, have been noted previously for the transport of lactate into hepatocytes (Edlund & Halestrap, 1988), and may reflect the presence of an anionic pathway capable of driving lactate out of the cell under the influence of the membrane potential, particularly when it is present at high concentrations. Such a pathway is thought to exist in striated muscle (Mason, 1986) and Lettre cells (Bashford & Pasternak, 1984).…”

Membrane potential difference and intracellular cation concentrations in human placental trophoblast cells in culture.

“…However, the median microvillous Em measured in villi isolated from term placentas bathed in C02-HC03-(pH 7 4) buffer at 37°C is -22 mV (Greenwood et al 1993a) (Bashford & Pasternak, 1984) (Leichtweiss, Carstensen, Schroder & Rachor, 1985). Na+ concentration was 84 mmol 1-F and K+ concentration 62 mmol 1-' in non-perfused, and 85 and 61 mmol 1-' in perfused placentas, respectively.…”