Renal function in normal and potassium-depleted rats before and after preparation for micropuncture experimentation

1. The contribution of apical Na¤-H¤ exchange to sodium reabsorption in the thick ascending limb of the loop of Henle (TALH) in vivo was examined in anaesthetized rats by perfusing loops of Henle of superficial nephrons with solutions containing the Na¤-H¤ exchange inhibitor, ethyl isopropyl amiloride (EIPA). 2. Using a standard perfusate, no statistically significant effect of EIPA on net sodium reabsorption (JNa) was detected. However, when sodium reabsorption in the pars recta of the proximal tubule was minimized by using a low-sodium perfusate, EIPA reduced JNa from 828 ± 41 to 726 ± 37 pmol min¢ (P < 0·05), indicating that apical Na¤-H¤ exchange can make a small contribution to net sodium reabsorption in the TALH in vivo. This contribution appears to be dependent on the bicarbonate load, since an increase in the latter led to an enhancement of EIPA-sensitive sodium transport. 3. Addition of the Na¤-K¤-2Cl¦ cotransport inhibitor, bumetanide, to the low-sodium perfusate reduced baseline JNa to 86 ± 27 pmol min¢. In this setting, EIPA reduced JNa further, to −24 ± 18 pmol min¢ (P < 0·05), an effect similar to that seen in the absence of bumetanide. This finding argues against previous suggestions (based on in vitro evidence) that inhibition of the Na¤-K¤-2Cl¦ cotransporter leads to an increase in apical Na¤-H¤ exchange in the TALH.

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“…These values fall within the normal ranges for Sprague-Dawley rats as documented in this laboratory (e.g. Shirley et al 1990;Unwin et al 1994). …”

Section: Whole Animal Datasupporting

confidence: 84%

Contribution of Na⁺‐H⁺ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats

Shirley

Walter

Unwin

et al. 1998

The Journal of Physiology

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“…The present study revealed that NHE3 abundance in the proximal tubules and TALs of rat kidney was significantly increased. Consistent with the increased abundance of NHE3 in the proximal tubules, micropuncture studies have previously shown that potassium depletion in rats was associated with substantially reduced lithium clearance, indicating that sodium and water delivery to the end of the proximal tubules was reduced (43), possibly due to increased proximal tubular reabsorption in hypokalemia (47).…”

Section: Increased Nhe3 Abundance In Proximal Tubules and Tals In Hypmentioning

confidence: 54%

Altered expression of renal NHE3, TSC, BSC-1, and ENaC subunits in potassium-depleted rats

Elkjær

Kwon

Wang

et al. 2002

American Journal of Physiology-Renal Physiology

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The purpose of this study was to examine whether hypokalemia is associated with altered abundance of major renal Na+ transporters that may contribute to the development of urinary concentrating defects. We examined the changes in the abundance of the type 3 Na+/H+ exchanger (NHE3), Na+-K+-ATPase, the bumetanide-sensitive Na+-K+-2Cl− cotransporter (BSC-1), the thiazide-sensitive Na+-Cl− cotransporter (TSC), and epithelial sodium channel (ENaC) subunits in kidneys of hypokalemic rats. Semiquantitative immunoblotting revealed that the abundance of BSC-1 (57%) and TSC (46%) were profoundly decreased in the inner stripe of the outer medulla (ISOM) and cortex/outer stripe of the outer medulla (OSOM), respectively. These findings were confirmed by immunohistochemistry. Moreover, total kidney abundance of all ENaC subunits was significantly reduced in response to the hypokalemia: α-subunit (61%), β-subunit (41%), and γ-subunit (60%), and this was confirmed by immunohistochemistry. In contrast, the renal abundance of NHE3 in hypokalemic rats was dramatically increased in cortex/OSOM (736%) and ISOM (210%). Downregulation of BSC-1, TSC, and ENaC may contribute to the urinary concentrating defect, whereas upregulation of NHE3 may be compensatory to prevent urinary Na+ loss and/or to maintain intracellular pH levels.

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“…Sprague-Dawley rats or Munich-Wistar rats were anesthetized with sodium thiopentone (100 mg/kg, intraperitoneally; Link Pharmaceuticals, Horsham, Sussex, UK) and prepared surgically for micropuncture of the left kidney (12). All animals received intravenous infusions of isotonic saline at 4 ml/h.…”

Section: Methodsmentioning

confidence: 99%

Intraluminal ATP Concentrations in Rat Renal Tubules

Vekaria¹,

Unwin²,

Shirley³

2006

Journal of the American Society of Nephrology

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It is becoming increasingly recognized that stimulation of apical P2 receptors can influence solute transport in the nephron, but, to date, no information is available on endogenous intraluminal nucleotide concentrations in vivo. This study measured intraluminal ATP concentrations in the renal tubules of anesthetized rats. Proximal tubular concentrations were found to be in the range of 100 to 300 nmol/L, with no significant variation along the S 2 segment, whereas concentrations in the early distal tubule were markedly lower. Using collections of varying duration, the half-life of ATP in collected proximal tubular fluid was found to be 3.4 min, indicating significant breakdown by soluble nucleotidases. For assessment of whether proximal tubular ATP was filtered or secreted, experiments were performed in Munich-Wistar rats. The ATP concentration in midproximal tubules (142 ؎ 23 nmol/L) was more than four-fold higher than in Bowman's space (32 ؎ 7 nmol/L; P < 0.001), whereas fractional water reabsorption between the two sites was modest. In experiments that were designed to determine the effects of (patho)physiologic disturbances on intraluminal ATP, rats were either volume expanded or subjected to hypotensive hemorrhage. Neither maneuver affected proximal tubular luminal ATP concentrations significantly; rapid degradation of secreted ATP by ecto-and soluble nucleotidases is a possible explanation. It is concluded that the proximal tubule secretes ATP into the lumen, where it may have an autocrine/paracrine regulatory role. T he epithelial cells of the mammalian nephron express a variety of P2Y and P2X receptor subtypes on their basolateral and apical membranes (1-3). 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. Before making such inferences concerning a functional role of intraluminal nucleotides, however, it is necessary to ascertain whether their normal endogenous concentrations are sufficient to activate P2 receptors and whether they can be influenced by physiologic/pathophysiologic maneuvers that are known to affect tubular transport. ATP secretion by renal epithelial cultures and by cell lines that were derived from ...

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Renal function in normal and potassium-depleted rats before and after preparation for micropuncture experimentation

Cited by 24 publications

References 21 publications

Contribution of Na⁺‐H⁺ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats

Contribution of Na⁺‐H⁺ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats

Altered expression of renal NHE3, TSC, BSC-1, and ENaC subunits in potassium-depleted rats

Intraluminal ATP Concentrations in Rat Renal Tubules

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Renal function in normal and potassium-depleted rats before and after preparation for micropuncture experimentation

Cited by 24 publications

References 21 publications

Contribution of Na+‐H+ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats

Contribution of Na+‐H+ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats

Altered expression of renal NHE3, TSC, BSC-1, and ENaC subunits in potassium-depleted rats

Intraluminal ATP Concentrations in Rat Renal Tubules

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Contribution of Na⁺‐H⁺ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats

Contribution of Na⁺‐H⁺ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats