EFFECTS OF HGCL2 ON INTRACELLULAR PH IN SEA-URCHIN EGGS - ACTIVATION OF H+ EXCRETION AND NA+ H+ EXCHANGE ACTIVITY/

The action of HgCl2 on intracellular pH (pH(i)) and H+ excretion has b een investigated in unfertilized and fertilized sea urchin eggs. The r esults show that HgCl2 in the micromolar range stimulated acid release by increasing the Na+/H+ antiporter activity in both unfertilized and fertilized eggs, altering pH(i) regulation and cell metabolism. Howev er, the mechanism of HgCl2-induced acid excretion appeared to be diffe rent before and after fertilization. Furthermore, HgCl2 induced cell a lkalinisation in unfertilized eggs and cell acidification in fertilize d eggs. The mechanism of HgCl2 alteration of pH(i) and origin of excre ted H+ were studied. In unfertilized eggs, it is postulated that HgCl2 stimulates the diacylglycerol pathway of the phosphatidyl-inositol cy cle probably by acting on protein kinase C in a similar manner to the phorbol ester TPA, leading to activation of the Na+/H+ exchange. In fe rtilized eggs, HgCl2 induced H+ excretion appeared to be dependent on an increase in Ca2+ influx, which in tum may have been responsible for activating the Ca2+-dependent Na+/H+ exchange. Furthermore, internal H+ production was stimulated: the cyanide-sensitive H+ source involved uncoupling of mitochondria, the cyanide-insensitive part of H+ produc tion likely resulted from action on acidic intracellular compartments, both events mediated by an HgCl2-induced Ca2+ release.