Kinetic Analyses of Calcium Movements in HeLa Cell Cultures

Abstract

Calcium influx was studied in monolayerg of HeLa cells to determine the number of exchangeable and nonexchangeable pools and the rate constant of the different fluxes. Of the two exchangeable pools, one has a very fast rate of exchange with a half-time of 1.54 illin, a compartment size of 1.06 m#moles/mg cell protein, and an exchange rate of 474 #/~moles/(mg protein. rain). This compartment is likely to be extracellular and could represent calcium exchange between the extracellular fluids and surface binding sites of the cell membrane. The second exchangeable pool has a half-time of exchange of 31 rain, a compartment size of 2.69 m/~moles/mg cell protein (0.224 millimole calcium/kg cell water), and a flux rate of 0.0546 v#mole cm -~ sec -t. This compartment can be considered to be the intracellular pool of exchangeable calcium. An unexchangeable intracellular pool of calcium of 3.05 m#moles/mg cell protein was detected implying that only 45 % of the intracellular calcium is exchangeable. In addition, a large extracellular pool of calcium has been found to be unexchangeable, probably a part of the cell glycocalix. Finally, dinitrophenol 10 -8 M does not affect the slow component of the calcium uptake curve which brings new evidence that calcium entry into the cell is not a metabolically dependent process.The study of cellular calcium metabolism presents several difficulties. A cell, for instance, cannot be considered an homogeneous pool of calcium. There are at least two calcium compartments of different magnitude showing markedly different properties (1, 2). One of these compartments is even not part of the cell itself but lies outside the plasma membrane and has been called "cell coat" or "glycocalix" (1-3). The second, the cellular calcium compartment, is undoubtedly divided into several pools, but for the time being we shall consider intracellular calcium as one compartment. Until now we have attempted to dissect these two main compartments by chemically stripping the ceils from their coat with trypsin-EDTA in order to identify the properties of 43

Selective loss of calcium permeability on maturation of reticulocytes.

“…This assiumptioIn is only approximate since retictulocytes are more osmotically resistant than matture cells which in(licates a slightly greater surface area-to-volume ratio of' these more immatuire cells (3). Whatever the exact valtues, it is clear that erythrocyte Ca21 permeability is many orders of magnitude less than for squiid axon, HeLa cells, or ascites tumor cells where fluix aluies about 0(.1 pmol/cm2 per s have been foOund (23)(24)(25).…”

A kinetic analysis of the effects of adrenaline on calcium distribution in isolated rat liver parenchymal cells

“…This proposal is currently under investigation. Borle, 1969). The latter approximation holds for total medium Ca > total cell Ca.…”

Activation of high levels of endogenous phospholipase A2 in cultured cells.

“…EDTA has been shown (24) to rapidly remove (half-life, 1.5 min) cell surface Ca2+ from HeLa cells, whereas a second larger pool, presumed to be cytoplasmic Ca2+, is removed by EDTA much more slowly (half-life, 31 min). Because chelating agents have been shown to have similar effects on the Ca2+ content of 3T3 cells (25), addition of 10 mM EDTA to the culture medium (which contains 1.8 mM CaCl2) would be expected to inhibit primarily cell surface PLase.…”