Stimulation of phosphorylation of rat brush-border membrane proteins by Escherichia coli heat-stable enterotoxin, cholera enterotoxin and cyclic nucleotides, and its inhibition by protein kinase inhibitors, isoquinolinesulfonamides.

Stimulation of phosphorylation of rat brush-border membrane proteins by the heat-stable enterotoxin of Escherichia coli (STh), cholera enterotoxin, cGMP and cAMP was demonstrated. Among at least 14 proteins examined, a protein with a molecular mass of 81,000 Da (81 kDa protein) was phosphorylated most in the presence of both STh and cholera enterotoxin, as well as in the presence of cGMP and cAMP. This phosphorylation was inhibited by N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8) or N-(2-aminoethyl)-5-isoquinoline-sulfonamide (H-9), which suggests that the phosphorylation occurs through cGMP- and cAMP-dependent protein kinases.