Transport of calcium ions by Ehrlich ascites tumor cells

Abstract

Ehrlich ascites tumor cells accumulate Ca2+ when incubated aerobically with succinate, phosphate and rotenone, as revealed by isotopic and atomic absorption measurements. Ca2+ does not stimulate oxygen 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 the 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 tri phosphate 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 that extracellular ATP increases permeability of the cell membrane, allowing both ATP and Ca2+ to enter the cells more readily.