Background: Guanylin and uroguanylin link intestinal and renal electrolyte and water transport. Their function in intestine is well studied, but renal actions are less understood. Uroguanylin concentrations are increased in patients with chronic renal failure, nephrotic syndrome, or those on dialysis. Guanylate cyclase C (GC-C) is the receptor first described for these peptides. In guanylate cyclase C-deficient mice guanylin- and uroguanylin-induced renal natriuresis, kaliuresis, and diuresis are retained.
Methods: Effects of guanylin and uroguanylin on principal cells of human cortical collecting ducts (CCD) isolated from kidneys after tumor nephrectomy were investigated. Reverse transcription-polymerase chain reaction (RT-PCR), slow whole-cell patch-clamp, and microfluorimetric analysis of intracellular Ca(2+) were used. Here we present first functional measurements of isolated human CCD.
Results: Principal cells of CCD were identified by the amiloride-induced hyperpolarization of principal cells (-3.8 +/- 0.3 mV) (N= 52). Cells depolarized upon guanylin or uroguanylin (each 10 nmol/L) by 3.3 +/- 0.8 mV (N= 12) and 3.4 +/- 0.5 mV (N= 18), respectively, but were hyperpolarized by 8Br-cyclic guanosine monophosphate (cGMP) (100 micromol/L) (-3.0 +/- 0.2 mV) (N= 4). mRNA for GC-C was not detected in CCD. Effects of both peptides were inhibited by Ba(2+) (1 mmol/L) or phospholipase A(2) (PLA(2)) inhibition (AACOCF(3)) (5 micromol/L).
Conclusion: These findings suggest a new cGMP- and GC-C-independent but PLA(2)-dependent signaling pathway for these peptides in the kidney. Most likely guanylin and uroguanylin inhibit luminal K(+) channels of principal cells of human CCD via this pathway. This depolarization of principal cells consequently reduces the driving force of Na(+) and water reabsorption, explaining natriuresis and diuresis caused by these peptides.