title: Mechanisms regulating intracellular pH in sea urchin eggs.
abstract: Intracellular pH (pHi) of sea urchin eggs (Paracentrotus lividus) was determined using DMO (dimethyloxazolidinedione) and a rapid filtration technique (P. Payan, J.P. Girard, R. Christen and C. Sardet (1981). Exp. Cell Res. 134, 339-344). Transfer of unfertilized or fertilized eggs from normal sea water into Na+-free artificial sea water leads to a progressive acidification and fall of intracellular Na+ content. A step rise in external Na+ to 10 meq causes a rapid but transient Na+ entry coupled to an excretion of H+, giving rise to a pHi increase. It is shown that the plasma membrane of unfertilized eggs contains a permanent and reversible Na+/H+ exchanger which contributes to the regulation of pHi. This exchange occurs with a 1:1 stoichiometry and is independent of metabolic energy. Proton excretion and sodium entry follow saturable kinetics with respect to external Na+ and are completely inhibited by amiloride. At fertilization, pHi increases from 7.38 to 7.64 and is maintained at this level by two separate mechanisms: (1) a Na+/H+ exchange with the same characteristics as in unfertilized eggs; (2) a H+-excreting system that is dependent on external Na+, amiloride sensitive, and requiring metabolic energy. The relationship between the permanent Na+/H+ exchange involved in pHi regulation and the transient Na+/H+ exchange occurring at fertilization is discussed.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004114:Dimethadione; D005260:Female; D005306:Fertilization; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007473:Ion Channels / Q000187:drug effects; D007700:Kinetics; D010063:Ovum / Q000378:metabolism*; D011522:Protons; D012617:Sea Urchins; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D015053:Zygote / Q000378:metabolism
chemical_list: D007202:Indicators and Reagents; D007473:Ion Channels; D011522:Protons; D000584:Amiloride; D012964:Sodium; D004114:Dimethadione