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J S Cook

Publications and source records attributed to J S Cook.

At least 73 records · Page 4Linked to original sources
PubMed1977

Role of the membrane potential in serum-stimulated uptake of amino acid in a diploid human fibroblast.

The Na+-dependent accumulation of alpha-aminoisobutyric acid (AIB), measured in normal growing and quiescent (serum-deprived) HSWP cells (human diploid fibroblast), was found to be twofold higher (AIB/in/AIBout = 20-25) under the normal growing conditions. Serum stimulation of quiescent cells increases their AIB concentrating capacity by approximately 70% within 1 hr. These observations suggest that the driving forces for AIB accumulation may be reversibly influenced by the serum concentration of the growth medium. Addition of valinomycin (Val) to cells preequilibrated with AIB causes an enhanced accumulation of AIB, suggesting that the membrane potential can serve as a driving force for AIB accumulation. After preequilibration with AIB in 6 mM K+, transfer to 94 mM K+ with Val results in a marked and rapid net loss of AIB. The effect of Val on the accumulation of AIB is greatest in quiescent cells, with the intracellular AIB concentrations reaching those seen both in Val-stimulated normal cells and in Val-stimulated serum-stimulated cells. By adjusting [K+]0, in the presence of Val, the membrane potential of growing cells can be matched to that of quiescent cells or vice versa. When this is done, the two accumulate AIB to the same extent. Hence the AIB accumulating capacity is characteristic of the membrane potential rather than of the growth state. In summary, these data suggest that the accumulation of AIB in HSWP cells is influenced by changes in membrane potential and that a serum-associated membrane hyperpolarization could be responsible for the increased capacity for AIB accumulation in serum-stimulated cells.

Aminoisobutyric Acids↗
PubMed1976

Reversible independent alterations in glucose transport and metabolism in cultured human cells deprived of glucose.

We have measured uptake of 3H-hexoses into diploid human cells by exposing them to brief pulses of isotopic sugar during the log-growth, subconfluent-growth, and confluent-growth (contact inhibited) phases of the strain HSWP derived from human skin. 3H-deoxyglucose appears to be taken up three times faster than 3H-glucose. After exposure to 3H-glucose for longer than one minute, the cells excrete approximately 70% of the isotope into the medium as lactate. If lactate production (and hence excretion) is abolished by treating the cellls with iodoacetic acid or dinitrofluorobenzene, neither of which inhibits transport, the uptake of 3H-glucose is found to be in fact somewhat larger than that of 3H-deoxyglucose. If cells are deprived of glucose for 24 hours, apparent uptake of 3H-glucose is enhanced 10-fold or more. This latter increase is accounted for by 2- to 3-fold enhancement of true transport plus retention of greater than 90% of the radioactivity, since little lactate is formed or excreted in glucose-deprived cells. Deoxyglucose, galactose, or pyruvate when present during glucose deprivation each have quantitatively different effects on the cells' capacity to produce lactate from a short pulse of glucose, but none of them prevents the enhancement of hexose transport. After restoration of 5 mM glucose to starved cells, their metabolsim returns to normal (in the sense that approximately 70% of the glucose taken up in a pulse is again excreted as lactate), with a half-time of 0.5 hour; but the transport of hexoses returns to control levels much more slowly, with a half-time of approximately 6 hours. The two processes appear to be independently regulated.

Biological Transport, Active↗
PubMed1975

Interaction of two mechanisms regulating alkali cations in HeLa cells.

The alkali cation content of HeLa cells is independent of culture density and of whether the cells are grown in suspension or attached to the culture vessel. With a cell doubling time of 28 hours, the cell K content turns over approximately once per hour. Following partial blockade of the alkali-cation transport system with ouabain, two distinct but interrelated mechanisms operate in the cellular response: (a) an increase in intracellular Na stimulates the pump so that the short-term alteration in electrolyte compostition is less than would be expected from the fraction of pump sites inhibited, and (b) there is a cycloheximide-sensitive recovery in transport capacity reflecting a restoration of functional transport sites to their normal density on the cell surface. Experimental manipulations that mimic the effect of ouabain lead to a stimulation of transport, but they do not result in an increase in the number of ouabain-binding sites on the surface. The data are consistent with a four-to-six hour turn-over of transport sites at the surface, but there is no evidence for a speicific induction of the transport system within this short-term recovery period.

Binding Sites↗
PubMed1972

Regeneration of cation-transport capacity in HeLa cell membranes after specific blockade by ouabain.

The cardiac glycoside, ouabain, inhibits alkali-cation transport in HeLa cells. It binds to 0.75 x 10(6) sites per cell, and the half-time for its dissociation is 16 hr. After partial blockade by ouabain, the cell generates new ouabain-binding sites, with total restoration of transport in 10% of a cell cycle( approximately 3 hr). This recovery requires protein synthesis and appears to be a response to altered cell-electrolyte content, since growth of cells in media with low K(+) concentration enhances the titer of the transport enzyme in a fashion similar to the effect of ouabain. Totally blocked cells do not recover.

Animals↗