Resealing to small solutes of white erythrocyte membranes after incubation with EDTA, Ca2+, salt, sucrose, phospholipase C

Species variability of erythrocyte transport ATPases in mammals

Na+, K(+)-ATPase, and Ca(2+)-ATPase in whole erythrocytes from five species of mammals (rat, mouse, guinea pig, golden hamster, rabbit) after cell treatment with Tween 20 (7.5 mg/ml) varied over a wide range: from 3.0 +/- 0.9 mumol Pi/hr/ml cells in rabbit to 27.3 +/- 4.9 mumol Pi/hr/ml cells in mouse for Na+, K(+)-ATPase and from 8.0 +/- 1.6 mumol Pi/hr/ml cells in hamster to 47.2 +/- 4.9 mumol Pi/hr/ml cells in mouse for Ca(2+)-ATPase. Differences were less pronounced in red cell ghosts. Fatty acid and phospholipid compositions of erythrocyte membranes were similar for all species. Nevertheless, the activity of Ca(2+)-ATPase in ghosts significantly correlated (r = -0.884) with the ratio of PC + SM/PE + PS in red cell membranes. Rabbit membranes had the lowest content of arachidonate. Rat hemolysate activated Na+, K(+)-ATPase in the ghosts from the animals of any species investigated, whereas the enzyme activation by the homohemolysate was characteristic only of the rat, mouse, and guinea pig ghosts. The data obtained suggest that there are differences in both activity and intracellular control of transport ATPase in erythrocytes of different mammals.

Combined effects of succinylcholine and calcium on membrane-bound acetylcholinesterase activity

The effects of succinylcholine and calcium (Ca2+), alone and together, on membrane-bound acetylcholinesterase ("true-type" cholinesterase) were examined using human erythrocyte ghosts to elucidate the combined pharmacological activity of succinylcholine and calcium in in vivo system. Succinylcholine inhibited the acetylcholinesterase by a mixed style. Calcium alone exhibited an inhibitory effect on the enzyme, but a biphasic effect together with succinylcholine: marked restoration of the enzyme activity at calcium concentrations lower than 6 mM and depression at its higher concentrations. It is suggested that calcium induces a conformational change of the enzyme protein leading to the altered binding capacity of succinylcholine. In anesthetic practice, therefore, the use of calcium may not be indicated for the treatment of SCh phase II block.

Fusion of erythrocyte ghosts induced by calcium phosphate. Kinetic characteristics and the role of Ca2+, phosphate and calcium-phosphate complexes

Using an assay which allows continuous monitoring of the mixing of aqueous contents during membrane fusion, we have investigated the kinetics of calcium-phosphate-induced fusion of erythrocyte ghosts. In the presence of 10 mM phosphate, the threshold concentration for Ca2+-induced fusion was 1.25 mM, while the optimal concentration was approx. 1.75 mM Ca2+. Further enhancement of the cation concentration (greater than or equal to 2 mM) inhibited fusion of the ghosts. Initiation of fusion required the addition of phosphate prior to the addition of Ca2+, indicating that the combined interaction of Ca2+ and phosphate in or at the plane of the bilayer was a prerequisite for the induction of fusion. Furthermore, fusion was greatly facilitated upon transformation of calcium phosphate in the bulk medium from an amorphous to a solid, crystalline phase. It is suggested that membrane aggregation, and hence fusion, is facilitated by the formation of crystalline calcium phosphate nucleating on the ghost membrane. La3+, Mg2+ and Mn2+ did not trigger the fusion process, although aggregation of the ghosts did occur. Under conditions where calcium phosphate precipitation was inhibited, lanthanum phosphate precipitates facilitated fusion after prior treatment of ghosts with phosphate and Ca2+. These results indicated that fusion-prone conditions were induced prior to calcium phosphate precipitation. It is proposed that prior to calcium phosphate precipitation membrane changes are induced by separate interaction of Ca2+ and phosphate with the ghost membrane. Such an interaction could then render the ghosts susceptible to fusion and as soon as conditions are provided allowing close contact between adjacent membranes, fusion will be observed.