Renal effects of serine-7 analog of lymphoguanylin in ex vivo rat kidney

Guanylin and uroguanylin compose a family of natriuretic, diuretic, and kal iuretic peptides that bind to and activate apical membrane receptor guanyly l cyclase signaling molecules in renal and intestinal epithelia. Recently, a complementary DNA encoding an additional member of the guanylin family of cGMP-regulating peptides was isolated from lymphoid tissues of the opossum and was termed lymphoguanylin (LGN). A peptide analog of opossum LGN was s ynthesized containing a single disulfide bond with the internal cysteine-7 replaced by a serine residue (LGN(Cys7-->Ser7)). The biological activity of LGN(Ser) was tested by using a cGMP bioassay with cultured T84 (human inte stinal) cells and opossum kidney (OK) cells. LGN(Ser) has potencies and eff icacies for activation of cGMP production in the intestinal and kidney cell lines that are 100- and 1,000-fold higher than LGN, respectively. In the i solated perfused rat kidney, LGN(Ser) stimulated a maximal increase in frac tional Na+ excretion from 24.8 +/- 3.0 to 36.3 +/- 3.3% 60 min after admini stration and enhanced urine flow from 0.15 +/- 0.01 to 0.24 +/- 0.01 ml.g(- 1).min(-1). LGN(Ser) (0.69 muM) also increased fractional K+ excretion from 27.3 +/- 2.3 to 38.0 +/- 3.0% and fractional Cl- excretion from 26.1 +/- 0 .8 to 43.5 +/- 1.9. A ninefold increase in the urinary excretion of cGMP fr om 1.00 +/- 0.04 to 9.28 +/- 1.14 pmol/ml was elicited by LGN(Ser), whereas cAMP levels were not changed on peptide administration. These findings dem onstrate that LGN(Ser), which contains a single disulfide bond like native LGN, activates guanylyl cyclase-C (GC-C) receptors in T84 and OK cells and may be very helpful in studying the physiological importance of activation of GC-C in vivo. LGN(Ser) also exhibits full activity in the isolated perfu sed kidney equivalent to that observed previously with opossum uroguanylin, suggesting a physiological role for LGN in renal function. Thus the single amino acid substitution enhances the activity and potency of LGN.