Desensitization of the serum effect on Na+ influx in cultured human fibroblasts
- 1 October 1984
- journal article
- research article
- Published by Wiley in Journal of Cellular Physiology
- Vol. 121 (1), 226-234
- https://doi.org/10.1002/jcp.1041210128
Abstract
Stimulation of an amiloride‐sensitive Na+ influx pathway, which mediates Na+/H+ exchange, has been postulated to be an important step in the initiation of DNA synthesis in quiescent human fibroblasts. If the elevation of intracellular Na+ or the alkalinization of intracellular pH resulting from the activation of this system is a trigger for subsequent mitogenic events, then its inactivation may also be important to cellular functions. We investigated the duration of the activation of Na+ influx by serum in human foreskin fibroblasts (HSWP). It was found that activation of Na+ influx by 10% serum was transient, declining with a t1/2 = 15 min. Similarly, the Na+ content of the cells rose rapidly following serum addition and decreased with a t1/2 = 15 min. In addition, both the lys‐bradykinin‐ and the vasopressin‐stimulated Na+ influx and Na+ content declined with a t1/2 of approximately 15 min. Similar results were obtained using both Tris‐buffered and Hepes‐buffered, amino‐acid‐free EMEM. Finally, the above experiments were repeated under conditions normally used to assess the mitogenic response of cells. It was found that in cells arrested in G0 by serum deprivation in CO2‐buffered EMEM, the serum activated Na+ flux was also transient with a t1/2 of approximately 20 min. The desensitization of cells to serum could be readily (t1/2 = 20′) reversed by a subsequent incubation of cells in serum‐free medium. Stimulation of Na+ influx by both the divalent cation ionophore A23187 and the phospholipase activator melittin in also desensitized rapidly, suggesting the process is independent of receptor downregulation. The desensitization during serum preincubation occurred in both low Na+ and low pH medium suggesting that the process is not due to negative feedback on the transport system via a rise in cellular Na+ concentration or a rise in intracellular pH. Although the mechanism of desensitization is at present not known, it is likely to be a physiologically important event.This publication has 24 references indexed in Scilit:
- Mitogens and melittin stimulate an increase in intracellular free calcium concentration in human fibroblastsBiochemical and Biophysical Research Communications, 1984
- Lys-bradykinin stimulates Na+ influx and DNA synthesis in cultured human fibroblastsCell, 1983
- Effect of the intracellular Ca+2 antagonist TMB-8 on serum-stimulated Na+ influx in human fibroblastsBiochemical and Biophysical Research Communications, 1982
- Rapid down regulation of insulin receptors in adipocytes artifact of the incubation bufferBiochemical and Biophysical Research Communications, 1981
- Tris(hydroxmethyl)aminomethane permits the expression of insulin-induced receptor loss in isolated rat adipocytesBiochemical and Biophysical Research Communications, 1981
- Sodium fluxes in human fibroblasts: Kinetics of serum‐dependent and serum‐independent pathwaysJournal of Cellular Physiology, 1981
- Sodium fluxes in human fibroblasts: Effect of serum, Ca+2, and amilorideJournal of Cellular Physiology, 1981
- MONOVALENT ION FLUXES AND THE CONTROL OF CELL PROLIFERATION IN CULTURED FIBROBLASTSAnnals of the New York Academy of Sciences, 1980
- IONICALLY MEDIATED INDUCTION OF MITOGENESIS IN CNS NEURONSAnnals of the New York Academy of Sciences, 1980
- IONIC TRIGGERS IN THE FERTILIZATION OF SEA URCHIN EGGSAnnals of the New York Academy of Sciences, 1980