Effect of uroguanylin on potassium and bicarbonate transport in rat renal tubules

Amorim J.B.O.; Musa-Aziz R.; Lessa L.M.A.; Malnic G.; Fonteles M.C.

Effect of uroguanylin on potassium and bicarbonate transport in rat renal tubules

Tipo

Artigo

Data de publicação

2006

Periódico

Canadian Journal of Physiology and Pharmacology

Citações (Scopus)

17

Autores

Amorim J.B.O.
Musa-Aziz R.
Lessa L.M.A.
Malnic G.
Fonteles M.C.

Resumo

The effect of uroguanylin (UGN) on K+ and H+ secretion in the renal tubules of the rat kidney was studied using in vivo stationary microperfusion. For the study of K+ secretion, a tubule was punctured to inject a column of FDC-green-colored Ringer's solution with 0.5 mmol KCl/L ± 10-6 mol UGN/L, and oil was used to block fluid flow. K+ activity and transepithelial potential differences (PD) were measured with double microelectrodes (K+ ion-selective resin vs. reference) in the distal tubules of the same nephron. During perfusion, K + activity rose exponentially, from 0.5 mmol/L to stationary concentration, allowing for the calculation of K+ secretion (J K). JK increased from 0.63 ± 0.06 nmol·cm-2·s-1 in the control group to 0.85 ± 0.06 in the UGN group (p < 0.01). PD was -51.0 ± 5.3 mV in the control group and -50.3 ± 4.98 mV in the UGN group. In the presence of 10-7 mol iberiotoxin/L, the UGN effect was abolished: J K was 0.37 ± 0.038 nmol·cm-2·s -1 in the absence of, and 0.38 ± 0.025 in the presence of, UGN, indicating its action on maxi-K channels. In another series of experiments, renal tubule acidification was studied, using a similar method: proximal and distal tubules were perfused with solutions containing 25 mmol NaHCO 3/L. Acidification half-time was increased both in proximal and distal segments and, as a consequence, bicarbonate reabsorption decreased in the presence of UGN (in proximal tubules, from 2.40 ± 0.26 to 1.56 ± 0.21 nmol·cm-2·s-1). When the Na +/H+ exchanger was inhibited by 10-4 mol hexamethylene amiloride (HMA)/L, the control and UGN groups were not significantly different. In the late distal tubule, after HMA, UGN significantly reduced JHCO3-, indicating an effect of UGN on H +-ATPase. These data show that UGN stimulated JK + by acting on maxi-K channels, and decreased JHCO3 - by acting on NHE3 in proximal and H+-ATPase in distal tubules. © 2006 NRC.