The Na+/H+ antiport is activated by serum and phorbol esters in proliferating myoblasts but not in differentiated myotubes. Properties of the activation process.
The properties of the Na+/H+ exchange system have been studied with 22Na+ uptake techniques at two stages of muscle development: proliferating myoblasts and differentiated myotubes. The characteristics of the interactions of the exchanger with external H+, with external Na+, and with amiloride or its more potent analogs are the same at both stages of development. Differences between the two stages of development concern: (i) the internal pH (pHi) dependence of the Na+/H+ exchanger, and (ii) the activation of the Na+/H+ exchanger by serum and phorbol ester which is observed in myoblasts but not in myotubes. Properties of the Na+/H+ exchanger in myoblasts after serum activation seem to be identical to those observed in myotubes with or without serum as if myotube formation stabilized a fully activated state of the exchanger. The activation of the myoblast Na+/H+ exchange system by serum is due to a shift of the pHi dependence towards alkaline pHi values and to an increase in the maximal activity of the Na+/H+ exchange system at acidic pH. Phorbol esters which are well-known activators of protein kinase C can only partially mimic the effects of serum on the Na+/H+ exchanger: they produce a shift of the pH dependence, but they do not increase the maximal activity at acidic pH.
Vigne
P
P
Frelin
C
C
Lazdunski
M
M
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001769:Blood; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D002455:Cell Division; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D024510:Muscle Development; D010703:Phorbol Esters / Q000494:pharmacology*; D010704:Phorbols / Q000494:pharmacology*; D051381:Rats; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002352:Carrier Proteins; D010703:Phorbol Esters; D010704:Phorbols; D017923:Sodium-Hydrogen Exchangers; C039465:5-dimethylamiloride; D004815:Epidermal Growth Factor; D000584:Amiloride; D012964:Sodium; D013755:Tetradecanoylphorbol Acetate