ACTIVATION OF PROTEIN-KINASE-C DURING CELL-VOLUME REGULATION IN EHRLICH MOUSE ASCITES TUMOR-CELLS

We have previously demonstrated that in Ehrlich cells a bumetanide-sen sitive Na+,K+,2Cl(-) cotransporter is activated during regulatory volu me decrease after cell shrinkage (hypertonic conditions) as well as du ring the late phase of regulatory volume decrease (hypotonic condition s). It is, however, quiescent under isotonic conditions. Using a prote in kinase C assay system (Amersham, UK) it is here demonstrated that h ypertonic cell shrinkage results in an increase in protein kinase C ac tivity to 174% within the first minute, concomitant with the activatio n of the Na+,K+,2Cl(-) cotransporter. Hypotonic cell swelling results in a late activation of protein kinase C concomitant with a late activ ation of the Na+,K+,2Cl(-) cotransporter. The activation of protein ki nase C during hypertonic as well as hypotonic conditions is inhibited by H-7. The more specific protein kinase C inhibitor chelerythrine inh ibited protein kinase C as well as the Na+,K+,2Cl(-) cotransporter to the same extent as did H-7. These results indicate the involvement of protein kinase C in the regulation of the Na+,K+,2Cl(-) cotransporter in Ehrlich ascites tumor cells during cell volume regulation.