Effect of ionophore A23187 upon membrane function and ion movement in human and toad erythrocytes

Abstract

Addition of 0.1-0.3 micronM A23187, a divalent cation ionophore, to human erythrocytes suspended in a 1.0 mM 45Ca2+ -containing buffer results in a small (approximately two fold) increase in [Ca2+]i, a significant decrease in osmotic fragility, and a decrease in intracellular K+ (100 mmoles/liter of cells to 70 mmoles/liter cells) without significant alteration of intracellular [Na+]. This decrease in [K+]i is associated with a significant decrease in packed cell volume and correlates directly with the observed alteration is osmotic fragility. Increasing extracellular K+ to 125 mM prevents the A23187-induced changes in osmotic fragility, K+ content and cell volume, but does not prevent the ionophore-induced uptake of 45Ca2+. Addition of 0.1-0.3 micronM A23187 to toad erythrocytes leads to an increase in 45Ca2+ uptake comparable to that observed in human erythrocytes, but does not alter osmotic fragility, cell volume or K+ content. Higher concentrations of ionophore (3.0-10.0 micronM) cause a 30- to 50-fold increase in 45Ca2+ uptake and concomitant change in K+ content, cell volume and osmotic fragility. These changes in cell properties can be prevented by increasing extracellular [K+] to 90 mM. The difference in sensitivity of the two cell types to A23187 is attributed to the presence of additional intracellular calcium pools within toad erythrocytes that prevent an increase in cytoplasmic Ca2+ until Ca2+ uptake is increased substantially at the higher concentrations of A23187.

Intracellular calcium and pathogenesis and antenatal diagnosis of Duchenne muscular dystrophy.

“…An increase in the calcium content of muscle nuclei7 and mitochondria8 in dystrophy has been reported, and mitochondrial calcium overload has been suggested as a possible mechanism for cell necrosis in muscle diseases. 9 The various membrane changes that have been reported in Duchenne muscular dystrophy might be accounted for by increased intracellular calcium; these include echinocyte formation,0 11 increased potassium efflux"2 13 and reduced deformability in erythrocytes,"4 and reduced capping in lymphocytes. "5 In muscle increased intracellular calcium might account for degeneration and increased protein degradation'6 17 and, through enhancement of calcium-activated proteases,8" 19 lead to muscle necrosis and weakness; and the resultant increase in interaction between myofilaments might account for the development of muscle contractures.…”

Spin label study of erythrocyte deformability. Ca2+-induced loss of deformability and the effects of stomatocytogenic reagents on the deformability loss in human erythrocytes in shear flow

“…Human erythrocytes maintain a low concentration of intracellular Ca 2+ ions at -0.1-1 uM by the calcium pump (Ca2`-Mg2`)-ATPase. When the intracellular Ca2" concentration is increased by a treatment with the calcium ionophore A23187, a series of complex biochemical reactions occurs including the activation of (Ca2+-Mg2+)-ATPase by Ca2+-binding calmodulin (21,28), the modification of the metabolism and composition of membrane lipids (1)(2)(3)13), and the efflux of K+ ions and water (28,30) (Gardos effect [16]). It is also known that with an increase in the intracellular Ca 2+ ion concentration, the cells suffer from a partial loss of the whole cell deformability (11,20,22,26,40,43).…”

The calcium ionophore A23187 stimulates glycoprotein secretion by the guinea pig gallbladder

“…Since calcium ionophores act by increasing the level of intracellular ionized calcium (18)(19)(20), this stimulatory response to A23187 supports the concept that cytoplasmic ionized calcium is involved in the secretion of glycoproteins by the gallbladder. Our studies do not exclude the possibility that the increase in glycoprotein secretion is attributable to a change in uptake of glucosamine.…”