Kinetics of cyclocreatine and Na+ cotransport in human breast cancer cells: mechanism of activity

The growth-inhibitory effect of cyclocreatine(CCr) and the kinetics of CCr andNa⁺ cotransport were investigatedin MCF7 human breast cancer cells and its adriamycin-resistant sublinewith use of ³¹P- and²³Na-NMR spectroscopy. Thegrowth-inhibitory effect in the resistant line occurred at a lower CCrconcentration and was more pronounced than in the wild-type line. Thiscorrelated with an ~10-fold higher affinity of CCr to the transporterin the resistant line. The passive diffusion coefficient of CCr wasalso higher in the resistant line by three- to fourfold. The transportof CCr was accompanied by a rapid increase in intracellularNa⁺. This increase was found todepend on the rate of CCr transport and varied differently with CCrconcentration in the two cell lines. It is proposed that thecotransport of CCr and Na⁺followed by increased Na⁺concentration, together with the accumulation of the highly charged phosphocyclocreatine, are responsible for cell swelling and death.

     

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Phytoplankton distribution along the eastern coast of the USA. Part VI. Shelf waters between Cape Henry and Cape May

The shelf area from Cape Henry to Cape May is located betweentwo adjacent shelf sections of greater concentrations of phytoplanktoncells. North of this area higher cell numbers are found in theNew York Bight, but these concentrations decrease southwardtoward Cape May. Here the Delaware plume offers some incrementin cell numbers, but the next major concentration of cells occursfather south within the Chesapeake Bay plume, before decreasingagain toward Cape Hatteras. Species composition for these areasof the mid-Atlantic Bight are similar.     

METABOLISM OF TISSUE CULTURES : III. A METHOD FOR MEASURING THE PERMEABILITY OF TISSUE CELLS TO SOLUTES

By using radioactive isotopes in tissue cultures, the rate of permeation of substances into cells can be measured independently of concurrent metabolic reactions of these substances. Techniques of obtaining and analyzing data are described. Examples are given using radioactive potassium and phosphorus. Using cultures of chick embryo muscle, turnover time for cell potassium is 6 hours, and for cell inorganic phosphate is 7 hours in the examples cited. Permeability rates, based on estimates of the cell surface involved and expressed as millimoles per cm.² per hour, are of the order of magnitude of 10^–6 for potassium and of 10^–7 for phosphate.