Renal HCO3- Reabsorption Is Differentially Modulated by Water Deprivation Depending on Food / Na+ Intake

Although kidneys are able to perform water balance dissociated from Na+ balance, hypovolemic dehydration, as seen during water deprivation (WD), modifies both. Moreover, WD can occur singly or together with food deprivation (FD) and, therefore, may differently alter such parameters. NHE3 is the major pathway for NaHCO3- in the proximal tubule and is important to volume balance, but the effect of WD on it is not well known. The goal of this work was to determine the effect of WD on HCO3- reabsorption (JHCO3-) and the role of food (FI) or Na (NaI) intake in this mechanism. Rats were kept for 24 hs with water ad libitum (CTRL) or in WD, and JHCO3- was measured by means of stationary microperfusion. WD decreased by 34% JHCO3- (vs CTRL), and this effect was NHE3-dependent, since the S3226(NHE3-inhibitor)-insensitive component of JHCO3- was not modulated by WD. Because NaI increases renal Na+ excretion and could influence JHCO3-, animals were kept in WD and fed with a deficient Na+ diet (DNa), to determine the ...