Transport of calcium ions by Ehrlich ascites-tumour cells

Abstract

Ehrlich ascites [mouse] tumor cells accumulate Ca2+ when incubated aerobically with succinate, phosphate and rotenone, as revealed by isotopic and atomic absorption measurements. Ca2+ does not stimulate O2 consumption by carefully prepared Ehrlich cells, but does so when the cells are placed in a hypo-osmotic medium. Neither glutamate nor malate support Ca2+ uptake in intact Ehrlich cells, nor does endogenous NAD-linked respiration. Ca2+ uptake is completely dependent on mitochondrial energy coupling mechanisms. It was an unexpected finding that maximal Ca2+ uptake supported by succinate requires rotenone, which blocks oxidation of endogenous NAD-linked substrates. Phosphate functions as co-anion for entry of Ca2+. Ca2+ uptake is also supported by extracellular ATP. No other nucleoside 5''-di- or triphosphate was active. The accumulation of Ca2+ apparently takes place in the mitochondria, since oligomycin and atractyloside inhibit ATP-supported Ca2+ uptake. Glycolysis does not support Ca2+ uptake. Neither free mitochondria released from disrupted cells nor permeability damaged cells capable of absorbing trypan blue were responsible for any large fraction of the total observed energy coupled Ca2+ uptake. The observations reported also indicate that electron flow through energy conserving site 1 promotes Ca2+ release from Ehrlich cells and extracellular ATP increases permeability of the cell membrane, allowing ATP and Ca2+ to enter the cells more readily.