Effects of Cardiotonic Steroids on Isolated Perfused Kidney and NHE3 Activity in Renal Proximal Tubules

Publication date: Available online 12 May 2017
Source:Biochimica et Biophysica Acta (BBA) - General Subjects
Author(s): Alana N. Godinho, Graciana T. Costa, Nádia O. Oliveira, Bruno A. Cardi, Daniel Esdras A. Uchoa, Edilberto R. Silveira, Luis Eduardo M. Quintas, François G. Noël, Manassés C. Fonteles, Krishnamurti M. Carvalho, Cláudia F. Santos, Lucília M.A. Lessa, Nilberto R.F. do Nascimento
Cardiotonic steroids (CS) are known as modulators of sodium and water homeostasis. These compounds contribute to the excretion of sodium under overload conditions due to its natriuretic property related to the inhibition of renal Na⁺/K⁺-ATPase (NKA) pump α1 isoform. NHE3, the main route for Na⁺ reabsorption in the proximal tubule, depends on the Na⁺ gradient generated by NKA pump. In the present study we aimed to investigate the effects of marinobufagin (MBG) and telocinobufagin (TBG) on the renal function of isolated perfused rat kidney and on the inhibition of NKA activity. Furthermore, we investigated the mechanisms for the cardiotonic steroids-mediated natriuretic effect, by evaluating and comparing the effects of bufalin (BUF), ouabain (OUA), MBG and TBG on NHE3 activity in renal proximal tubule in vivo. TBG significantly increased GFR, UF, natriuresis and kaliuresis in isolated perfused rat kidney, and inhibits the activity of NKA at a much higher rate than MBG. By stationary microperfusion technique, the perfusion with BUF, OUA, TBG or MBG promoted an inhibitory effect on NHE3 activity, whereas BUF was the most effective agent, and demonstrated a dose-dependent response, with maximal inhibition at 50nM. Furthermore, our data showed the role of NKA - Src kinase pathway in the inhibition of NHE3 by CS. Finally, a downstream step, MEK1/2-ERK1/2 was also investigated, and, similar to Src inhibition, MEK1/2 inhibitor (UO126) suppressed BUF effect. Our findings indicate the involvement of NKA-SRc-Kinase-Ras-Raf-ERK1/2 pathway in the downregulation of NHE3 by cardiotonic steroids in renal proximal tubule, promoting a reduction of the proximal sodium reabsorption and natriuresis.



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