Membrane transport properties differ following return of serum‐deprived versus Ca++‐deprived human fibroblasts to a proliferative state

Joseph T. Tupper, William T. Ryals, Peter V. Bodine

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7 Scopus citations


Human lung fibroblasts (W138) can be brought to a quiescent state by removal of serum from the medium or by lowering of the extracellular Ca++. Upon return of Ca++ or serum, the cells enter the G1 phase and progress to S within 15–18 hours. Since multiple G1 phase blocks have been demonstrated, we wished to determine whether the Ca++ and serum block were equivalent since previous data suggested that these two medium components may act at a common point in the initiation of proliferation. We have evaluated the membrane transport of 86Rb, 3‐O‐methylglucose, AIB, and cycloleucine following stimulation of quiescent cells by Ca++ or serum. Serum stimulation results in large increases in the influx of all the substances tested. These increases are prevented if Ca++ is absent upon serum stimulation or they are rapidly diminished following Ca++ removal. In contrast, Ca++ stimulation of Ca++‐deprived cells causes little or no enhancement of any of the transport systems, yet the cells progress to S phase in a manner similar to serum‐stimulated cells. These results indicate that the Ca++ and serum G0 or G1 block are not equivalent and that the serum‐induced change in transport of these components does not appear necessary for successful G1 phase progression. Furthermore, the data suggest that the sequence in which Ca++ or serum are presented to the cells alters the ability of Ca++ to modulate the transport systems. Quiescent cells which are exposed to Ca++ prior to serum possess a Ca++ modulation of several transport systems. Cells which are exposed to Ca++ subsequent to serum do not appear to possess this Ca++ regulation.

Original languageEnglish (US)
Pages (from-to)29-34
Number of pages6
JournalJournal of Cellular Physiology
Issue number1
StatePublished - Jan 1982

ASJC Scopus subject areas

  • Physiology
  • Clinical Biochemistry
  • Cell Biology


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