Morphometrical analysis of the gap-junctional area in parenchymal cells of the rat liver after administration of dibutyryl cAMP and aminophylline.

In view of the presumed involvement of gap junctions in the coordination of metabolic activities, the influence of cAMP as a regulatory signal of cell metabolism on gap junctions of hepatocytes has been examined. Male rats received two intraperitoneal doses of 10 mg dibutyryl cAMP/100 g body weight with a time interval of 2.5 h and were decapitated 2.5 h later. After this 5-h interval, analysis of freeze-fracture replicas of fixed liver tissue revealed an increase in the mean (+/- SEM) gap-junctional membrane portion on the lateral hepatocyte membranes from 0.049 +/- 0.003 (n = 66) in controls to 0.061 +/- 0.003 (n = 70) in treated rats, while the configuration of the connexons appeared unaltered. This effect could not be reinforced by prior administration of aminophylline: the relative gap-junctional area is similarly extended from 0.054 +/- 0.003 (n = 126) in the control group to 0.065 +/- 0.004 (n = 105) in the experimental animals. Probing for the time course of the junctional response, a group of rats was sacrificed 3 h after the onset of treatment. Already within this time, the gap-junctional area is augmented from 0.042 +/- 0.004 (n = 63) in the concurrent controls to 0.069 +/- 0.006 (n = 42) in the treated rats. These statistically significant increases in area may suggest a stimulating effect of cAMP on gap junctions of hepatocytes in vivo.