ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary As part of a genetic study of the mechanisms for cation transport in cultured mammalian cells, two mouse fibroblastic cell lines have been compared with respect to unidirectional42K+ influx. The cell lines areLM(TK −) andLTK-5, a mutant selected fromLM(TK −) by the ability to grow in medium containing 0.2mm K+. In both cell lines, the overall influx can be resolved into three components: (i) a ouabain- and vanadate-sensitive component ( i MK f), presumably the Na/K pump, which is a saturable function of extracellular K+ with aK 1/2 of 1.3mm; (ii) a furosemide-sensitive component ( i Mk fx), also a saturable function of extracellular K+, with aK 1/2 of 6mm; and (iii) a diffusional component ( i Mk d); which is a linear function of extracellular K+. By several independent criteria, i Mk o and i Mk f appear to be distinct transport processes. First, as indicated above, they can be separated with the use of inhibitors. In addition, they can be separated genetically, since theLTK-5 mutant shows a threefold elevation in i Mk f with no change in i Mk o. And finally, extracellular Na+ has no effect on i Mk o, but stimulates i Mk f, a result consistent with the notion that i Mk f influx occurs by Na−K cotransport. Further experiments were directed towards understanding the nature of theLTK-5 mutation and the physiological role of i Mk f. LTK-5 differs from the parental cell line, not only in having an increased i Mk f, but also in having a large cell volume, a slow maximal growth rate, and an ability to grow at 0.2mm K+. The most straightforward interpretation — that the increased i Mk f is itself responsible—is unlikely since the addition of furosemide to the growth medium had no effect upon the growth rate or cell volume of the mutant at either normal or low extracellular K+ concentrations. It did, however, render the parent capable of growth at 0.2mm K+. Possible interpretations are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01869193
