Humoral immunostimulation: X. Cytochalasin B stimulates complement-dependent calcium uptake in antibody-treated cells

Abstract

Cytochalasin B exerted a biphasic effect upon the uptake of calcium in L cells treated with anti-L-cell antibody and complement. At a high concentration (1 × 10 −4 M), cytochalasin B inhibited the antibody- and complement-induced stimulation of calcium uptake into L cells; whereas, at a lower concentration (1 × 10 −6 M), the drug enhanced uptake. Cytochalasin B-induced stimulation of calcium uptake was exclusively dependent upon the concentration of the antibody-antigen-activated complement system since the drug did not enhance calcium uptake in cells treated with antibody alone nor in cells treated with antibody and heat-inactivated complement. Moreover, when special serums deficient or depleted of certain complement components were used as sources of complement, there was a loss of the enhancement of calcium uptake. Thus, guinea pig serums deficient in C4 or C3-C9, human serums deficient in Cl r, C2, C2,4 or C4, and rabbit serums deficient in C3-C9 or C6 all failed to permit enhanced calcium uptake in antibody-treated cells in the presence of 1 × 10 −6 M cytochalasin B in contrast to normal guinea pig, human, or rabbit serums. Stimulation of calcium uptake in antibody- and complement-treated cells by cytochalasin B was exquisitely dependent upon cellular energy sources since the stimulation was abrogated when uptake studies were performed in the presence of the metabolic inhibitors, dinitrophenol and iodoacetate. Enhanced calcium uptake by cytochalasin B was not due to simple increased intracellular volume of treated cells nor to increased antibody (IgG) binding. Likewise, antibody and complement did not alter either high- or low-affinity binding of Cytochalasin B to cells. Substrate saturation studies suggested that the enhanced calcium uptake in the presence of cytochalasin B was due to an increase in the V max of transport with utilization of the same K m. CB did not appear to produce this effect upon calcium transport through its well-known effects upon glucose transport since CB augmented calcium uptake in the absence as well as in the presence of glucose. In summary, it appears that cytochalasin B modulates calcium uptake in antibody-treated L cells via interaction with an intact complement pathway and that the effect is due to an energy-requiring activation of the components of a transport system.