the locus of theophylline or db-camp action appears to be at the epithelial apical membrane where increased intracellular camp or other cyclic nucleotide such as guanosine 3',5'-cyclic monophosphate ( cgmp ) may interact directly or through another agent , such as the divalent cation ca2+ , to reduce or eliminate coupled na+-cl- influx into the cell from the gut lumen .
C1708726
locus
C0007634
cell