ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Enhanced uptake of amino acids is frequently associated with hyperplasia in cultured cells; we have recently shown (Merrill et al., '77) that this is true of the stimulation of rat myoblast proliferation in culture by Temin's Multiplication Stimulating Activity (MSA). In many cases the asymmetric distribution of Na+ and K+ across the cell membrane profoundly affects uptake of certain amino acids, so we investigated the possibility that enhanced Na+-dependent AIB transport was the result of an MSA-induced increase in K+ accumulation. MSA stimulated the rate of uptake of the potassium analog 86Rb+ 15-25% within ten minutes; this rate remained elevated for at least seven hours. Effects were limited to the ouabain-sensitive component of Rb+ uptake. (Our simultaneous measurements of 86Rb+ and 42K+ uptake demonstrated that Rb+ provides a useful qualitative but not an exact quantitative index of K+ uptake.) The stimulation of K+ uptake by MSA did not cause a large increase in total cellular K+ of the myoblasts; after five hours, MSA-treated cells contained only about 20% more K+ than did corresponding controls (1.21 ± 0.02 vs. 1.01 ± 0.02 μmoles/mg protein, respectively). To investigate whether this small increase in K+ content could be amplified by the cell to account for the 50-150% stimulation of AIB uptake, we preincubated cells with ouabain for various times and then measured total cell K+ and AIB uptake in the same culture dishes. Under conditions in which the MSA-stimulated increase of total cell K+ was prevented by ouabain, a substantial stimulation of AIB uptake was still observed. We conclude that MSA stimulation of AIB transport is independent of increased accumulation of K+ in rat myoblasts.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041000215
