Attenuation of lithium-induced natriuresis and kaliuresis in P2Y₂receptor knockout mice

Abstract

receptor activity and increased renal Na ϩ conservation. We hypothesized that P2Y2R KO mice would be less sensitive to lithiuminduced natriuresis and kaliuresis due to attenuated downregulation of one or more of the major renal Na ϩ or K ϩ transporter/channel proteins. KO and wild-type (WT) mice were fed a control or lithiumadded diet (40 mmol/kg food) for 14 days. Lithium-induced natriuresis and kaliuresis were significantly (ϳ25%) attenuated in KO mice. The subunits of the epithelial Na ϩ channel (ENaC) were variably affected by lithium and genotype, but, overall, medullary levels were decreased substantially by lithium (15-60%) in both genotypes. In contrast, cortical, ␤-, and ␥-ENaC were increased by lithium (ϳ50%), but only in WT mice. Moreover, an assessment of ENaC activity by benzamil sensitivity suggested that lithium increased ENaC activity in WT mice but in not KO mice. In contrast, medullary levels of Na ϩ -K ϩ -2Cl Ϫ cotransporter 2 and cortical levels of the renal outer medullary K ϩ channel were not downregulated by lithium and were significantly (15-76%) higher in KO mice under both dietary conditions. In addition, under control conditions, tissue osmolality of the inner medulla as well as furosemide sensitivity were significantly higher in KO mice versus WT mice. Therefore, we suggest that increased expression of these proteins, particularly in the control state, reduces Na ϩ delivery to the distal nephron and provides a buffer to attenuate collecting duct-mediated natriuresis and kaliuresis. Additional studies are warranted to explore the potential therapeutic benefits of purinergic antagonism.vasopressin; aldosterone; sodium transporters; epithelial sodium channel; potassium channels; ATP; nephrogenic diabetes insipidus DESPITE THE ADVENT of newer medications, lithium continues to be the main choice for the treatment of bipolar disorder due to its ability to prevent suicidal tendencies (12,24). However, the adverse effects of chronic lithium treatment on the kidney leading to nephrogenic diabetes insipidus (NDI) is a major limiting factor in the use of this effective medication (for a review, see Ref. 11). In addition, lithium has been shown to have a myriad of other effects in the kidney (for a review, see Ref. 15). Clinically, lithium-induced NDI is characterized by polyuria, natriuresis, and kaliuresis as well as the loss of other vital substances in the urine. Arginine vasopressin (AVP)-resistant polyuria causes dehydration, hypovolemia, and hypernatremia, leading to hemodynamic instability in elderly patients (23). On the other hand, lithium-induced natriuresis and kaliuresis activate mechanisms that result in renal lithium retention and lithium intoxication, which can become a vicious cycle (1, 34). Currently used therapeutic measures for lithiuminduced NDI, such as the use of cyclooxygenase (COX) inhibitors or thiazides, can also cause lithium intoxication, thus limiting their clinical use (25,35). Although administration of amiloride ameliorated lithium-induced polyuria, it markedly en...

Impaired natriuretic response to high-NaCl diet plus aldosterone infusion in mice overexpressing human CD39, an ectonucleotidase (NTPDase1)

“…First, we and others (23,35) observed that genetic deletion of P2Y 2 receptor per se upregulates the protein abundance of NKCC2 in the medulla, and is associated with increased natriuresis in response to acute furosemide treatment. However, another group (13) using P2Y 2 receptor-knockout mice with a different genetic background, did not observe upregulation of NKCC2 protein or transepithelial transport compared with WT mice.…”

“…Cortical and medullary tissue samples were processed separately as previously described (35,36) and shipped to Georgetown University for semiquantitative immunoblot analysis. Briefly, samples were prepared by homogenizing the frozen tissues in a buffer containing protease inhibitors.…”

“…For immunoblotting, 10 -30 g of protein from each sample was loaded into individual lanes of minigels of 7, 10, or 12% polyacrylamide (precast; BioRad, Hercules, CA). After electrotransfer of size-fractionated proteins to nitrocellulose membranes, blots were probed with our own rabbit peptide-derived polyclonal antibodies against the sodium-hydrogen exchanger type 3 (NHE3); the bumetanide-sensitive NKCC2; the thiazide-sensitive Na-Cl cotransporter (NCC); the sodium phosphate cotransporter-type 2 (NaPi-2); and the alpha, beta, and gamma subunits of the epithelial sodium channel (␣-ENaC, ␤-ENaC, and ␥-ENaC, respectively), as previously described (35,36). We used commercially available antibodies against the ␣-1 subunit of Na-K-ATPase (05-369; Millipore, Temecula, CA).…”

Prasugrel suppresses development of lithium-induced nephrogenic diabetes insipidus in mice

“…Unless otherwise stated, mice were housed in groups in conventional plastic cages with bedding and regulated light-dark cycles and had free access to food and drinking water. NDI was induced by the administration of LiCl by the methods established in our laboratory [10,[14][15][16]. Age-matched adult male mice were randomly divided into four groups (five mice/group).…”

“…Based on this deduction, we posited that the same actions of extracellular nucleotides mediated by P2Y receptors may also contribute to the development of collecting duct resistance to AVP often seen in acquired nephrogenic diabetes insipidus (NDI), such as the one induced by chronic lithium administration for the treatment of bipolar disorder [11][12][13]. Accordingly, we demonstrated that genetic deletion of P2Y 2 receptor confers significant resistance for the development of lithium-induced NDI [14,15]. However, currently, there are no FDA-approved selective antagonists of the P2Y 2 receptor, thus limiting our in vivo studies using pharmacological approach on this receptor.…”