The Na+/H+ exchanger is constitutively activated in P19 embryonal carcinoma cells, but not in a differentiated derivative. Responsiveness to growth factors and other stimuli

• Published in: The Journal of biological chemistry 1987-07, Vol.262 (20), p.9621-9628
• Main Authors: Bierman, A J, Tertoolen, L G, de Laat, S W, Moolenaar, W H
• Format: Article
• Language: English
• Subjects: Ammonia - pharmacology; Animals; Biological and medical sciences; Carrier Proteins - metabolism; Cell Differentiation; Cell differentiation, maturation, development, hematopoiesis; Cell Line; Cell Membrane - metabolism; Cell physiology; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Kinetics; Membrane Potentials; Mice; Molecular and cellular biology; Sodium-Hydrogen Exchangers; Teratoma - metabolism; Teratoma - pathology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)47979-3

We have examined the functional properties and growth factor responsiveness of the plasma membrane Na+/H+ exchanger in pluripotent P19 embryonal carcinoma (EC) cells and in a differentiated mesodermal derivative (MES-1) by analyzing the recovery of cytoplasmic pH (pHi) from an acute acid load under bicarbonate-free conditions. In the absence of exogenous growth factors, the mean steady-state pHi of undifferentiated P19 cells (7.49 +/- 0.03) is 0.55 unit higher than the value of differentiated MES-1 cells (6.94 +/- 0.01). In both cell types, recovery of pHi from an NH+4-induced acid load follows an exponential time course and is entirely mediated by the amiloride-sensitive Na+/H+ exchanger in the plasma membrane. Kinetic analysis indicates that the higher steady-state pHi in P19 EC cells is due to an alkaline shift in the pHi sensitivity of the Na+/H+ exchange rate, as compared to that in MES-1 cells. The Na+/H+ exchanger of MES-1 cells is responsive to epidermal growth factor, platelet-derived growth factor, serum, phorbol esters, and diacylglycerol, as shown by a rapid amiloride-sensitive rise in pHi of 0.15-0.35 unit. This mitogen-induced alkalinization is attributable to an alteration in the pHi sensitivity of the exchanger. In contrast, the Na+/H+ exchanger of P19 EC cells fails to respond to any of these stimuli. Similarly, hypertonic medium rapidly activates the Na+/H+ exchanger in MES-1, but not in P19 EC cells. We conclude that the Na+/H+ exchanger in undifferentiated P19 EC stem cells is maintained in a fully activated state which is unaffected by extracellular stimuli, as if signal pathways normally involved in growth factor action are constitutively operative.