Fig. 5. cAMP enhances GJIC, ß-casein and connexin expression by CID-9 cells on day 6 of culture in differentiation medium. Cells were plated on plastic in the absence (Ctrl; control) or presence of 50 µM 8-Br-cAMP (cAMP). (A) LY dye transfer in scrape-loaded cells was enhanced by cAMP. Integrated fluorescence intensity, quantified from three different experiments as described in Materials and Methods, showed a 3.2-fold increase (P<0.01). Phase contrast light micrograph showing altered clustering behaviour in cells treated with cAMP. (B) Northern blot analysis of ß-casein for cells plated on (Ctrl) plastic, and (cAMP) plastic plus 50 µM 8-Br-cAMP. 28S rRNA demonstrates equal loading. (C) Western blot for ß-casein, Cx43, Cx26 and ß-actin for CID-9 cells plated on (Ctrl) plastic, and (cAMP) plastic plus 50 µM 8-Br-cAMP. ß-actin western blot demonstrates equal loading. Western blot analysis showed a significant increase in ß-casein (P<0.01), Cx43 (P<0.05) and Cx26 (P<0.001) levels.