Inhibition of bicarbonate reabsorption in the rat proximal tubule by activation of luminal P2Y₁receptors

Abstract

The present study used a stationary microperfusion technique to investigate in vivo the effect of P2Y1 receptor activation on bicarbonate reabsorption in the rat proximal tubule. Proximal tubules were perfused with a bicarbonate Ringer solution before flow was stopped by means of an oil block. The recovery of lumen pH from the initial value (pH 8.0) to stationary values (pH approximately 6.7) was recorded by a H+-sensitive microelectrode inserted downstream of the perfusion pipette and oil block. The stationary pH value and the t(1/2) of pH recovery were used to calculate bicarbonate reabsorption (JHCO3). Both EIPA and bafilomycin A1 caused significant reductions in proximal tubule JHCO3, consistent with the established contributions of Na/H exchange and H+-ATPase to proximal tubule HCO3 reabsorption. The nucleotides ADP and, to a lesser extent, ATP reduced JHCO3 but AMP and UTP were without effect. 2MeSADP, a highly selective agonist of the P2Y1 receptor, reduced JHCO3 in a dose-dependent manner. MRS-2179, a P2Y1 receptor-specific antagonist, abolished the effect of 2MeSADP, whereas theophylline, an antagonist of adenosine (P1) receptors, did not. The inhibitory action of 2MeSADP was blocked by inhibition of protein kinase C and reduced by inhibition of protein kinase A. The effects of EIPA and 2MeSADP were not additive. The data provide functional evidence for P2Y1 receptors in the apical membrane of the rat proximal tubule: receptor activation impairs acidification in this nephron segment.

Relative contribution of V‐H+ATPase and NA+/H+ exchanger to bicarbonate reabsorption in proximal convoluted tubules of old rats

“…The bafilomycinsensitive acidification was significantly smaller than the EIPAsensitive one, showing that normal acidification is carried out mostly by an EIPA-sensitive mechanism. These results concur with data on bicarbonate reabsorption obtained with a similar experimental approach (Bailey, 2004). In NHE3 -/-mice, bicarbonate reabsorption is reduced 50-60% (Schultheis et al, 1998), a figure close to that reported in the present work.…”

“…We also confirm that a large fraction (∼60%) of bicarbonate reabsorption in the rat proximal tubule is dependent on the operation of an EIPA-sensitive mechanism (Preisig et al, 1987;Wang et al, 1999Wang et al, , 2001Bailey, 2004). In agreement with others (Wang et al, 1999(Wang et al, , 2001Bailey, 2004), we found a significant component of bicarbonate transport mediated by the bafilomycin-sensitive V-H + ATPase in the proximal tubules of both young and old rats. The bicarbonate reabsorption in proximal convoluted tubules of 3-month-old rats, either with EIPA or with bafilomycin in the luminal solution, were, respectively, 60% and 30% lower than the measured under control conditions.…”

Purinergic signaling in the lumen of a normal nephron and in remodeled PKD encapsulated cysts

“…Bailey et al detected mRNA for P2Y1, 2, 4, and 6 in glomeruli that was confirmed by functional analysis using inositol phosphate production as an endpoint [90]. They confirmed P2Y 1 receptor expression in the proximal tubule, showing inhibition of bicarbonate reabsorption [88]. They also assessed the expression of basolateral P2Y receptors along the nephron by applying different agonists to the bath in isolated nephron segment preparations [89].…”

Intraluminal ATP Concentrations in Rat Renal Tubules

“…When stimulated by application of exogenous nucleotides, these P2 receptors can influence a number of transport processes. Thus, activation of basolateral P2 receptors in the collecting duct inhibits vasopressin-stimulated water reabsorption (4 -6), and stimulation of apical P2 receptors can affect solute transport in both the proximal and the distal nephron: a recent in vivo micropuncture study in the rat showed that stimulation of apical P2Y 1 receptors inhibits proximal tubular bicarbonate reabsorption through suppression of NHE3 activity (7), and in vitro and in vivo evidence indicates that stimulation of apical P2 receptors in the distal nephron inhibits amiloride-sensitive sodium reabsorption (8,9) and reduces the activity of apical K ϩ secretory channels (10). These findings clearly support the proposal that intraluminal nucleotides, acting on apical P2 receptors, can function as autocrine/paracrine regulators of tubular transport.…”