CALMODULIN EXPRESSION DURING RAT-LIVER REGENERATION

We have investigated the messenger RNAs expressed from the three calmo dulin genes during rat liver regeneration. The results revealed that a ll the calmodulin transcripts increased from 8 hr after a partial hepa tectomy, although differences in the timing and the level of expressio n from the three genes were observed. Calmodulin I transcripts peaked at 16 hr, whereas calmodulin II and calmodulin III progressively incre ased from 8 to 24 hr. At 24 hr after surgery, calmodulin I, calmodulin II and the 2.3 kb calmodulin m transcripts reached values of a 6-fold increase, whereas the 0.8 kb product of calmodulin III increased 25-f old. At 30 hr the levels of all the calmodulin transcripts were simila r to those observed at 24 hr. The transcription rates of the three cal modulin genes augmented after hepatectomy (calmodulin I and calmodulin II twofold and calmodulin III fourfold), indicating that the elevatio n of the calmodulin transcripts could be, at least partially, the resu lt of this increase in the transcription rates. The total calmodulin c oncentration also increased twofold at 24 hr after hepatectomy. We als o report that the administration of the beta-adrenergic blocker, D,L-p ropranolol inhibited the accumulation of calmodulin protein without si gnificantly affecting the increase of the messenger RNAs. These result s indicate that the expression of calmodulin observed during liver reg eneration could be regulated by cyclic AMP at the translational or pos ttranslational level.