Asymmetric release of cyclic AMP from guinea-pig and rabbit gallbladder

Summary The release of cyclic adenosine 3:5-monophosphate (cAMP) from guinea-pig and rabbit gallbladder was investigated in vitro. Serosal addition of prostaglandin E₁ (PGE₁) to luminally perfused guinea-pig gallbladders caused a concentration-dependent efflux of cAMP to the mucosal side, the threshold concentration of PGE₁ being 10^–7 M. The efflux of cAMP to the serosal side was 7-fold lower. A mucosal sidedness of cAMP release was also observed in stripped preparations of rabbit gallbladder mucosa mounted between two half chambers. No cAMP was found in the solutions bathing the serosal layers isolated from rabbit gallbladders. Fluid secretion was observed at 10^–7 M PGE₁, an effect mimicked by serosal, but not mucosal application of cAMP (3.3×10^–3 M). This is taken to indicate that the basolateral membrane is more easily permeated by cAMP than the apical membrane, since cAMP is believed to exerts its physiological effects from inside the cell. It is concluded that preferential release of cAMP to the mucosal side is not due to a higher permeability of the brush border membrane but rather represents an as yet undefined transport process which may be of importance for the regulation of excessive intracellular cAMP levels.