Changes in renal medullary transport proteins during uncontrolled diabetes mellitus in rats

Abstract

Changes in renal medullary transport proteins during uncontrolled diabetes mellitus in rats. Am J Physiol Renal Physiol 285: F303-F309, 2003. First published April 15, 2003 10.1152/ajprenal.00438.2002We tested whether the abundance of transport proteins involved in the urinary concentrating mechanism was altered in rats with uncontrolled diabetes mellitus (DM). Rats were injected with streptozotocin and killed 5, 10, 14, or 20 days later. Blood glucose in DM rats was 300-450 mg/dl (control: 70-130 mg/dl). Urine volume increased in DM rats from 41 Ϯ 7 ml/100 g body wt (BW) at 5 days to 69 Ϯ 3 ml/100 g BW at 20 days (control: 9 Ϯ 1). Urine osmolality of DM rats decreased at 5 days DM and remained low at 20 days. UT-A1 urea transporter protein in the inner medullary (IM) tip was 55% of control in 5-day DM rats but increased to 170, 220, and 280% at 10, 14, and 20 days DM, respectively, due to an increase in the 117-kDa glycoprotein form. UT-A1 in the IM base was increased to 325% of control at 5 days DM with no further increase at 20 days. Aquaporin-2 (AQP2) increased to 290% in the IM base at 5 days DM and 150% in the IM tip at 10 days; both showed no further increase at 20 days. NKCC2/ BSC1 increased to 240% in outer medulla at 20 days DM, but not at 5 or 10 days. UT-B and ROMK were unchanged at any time point. The increases in UT-A1, AQP2, and NKCC2/ BSC1 proteins during uncontrolled DM would tend to limit the loss of fluid and solute during uncontrolled diabetes. urea; water; urea transporter; aquaporin; sodium PATIENTS WITH UNCONTROLLED type I diabetes mellitus (DM) are polyuric due to the osmotic diuresis caused by glucosuria. The persistent osmotic diuresis frequently results in a serious degree of volume depletion, but these patients rarely present for medical attention with shock and cardiovascular collapse. Instead, they generally present with severe hyperglycemia and diabetic ketoacidosis. This clinical presentation suggests the hypothesis that compensatory changes occur within the kidney that permit sufficient solute and water reabsorption, despite the ongoing osmotic diuresis, to prevent hypovolemic shock.The goal of this study was to test this hypothesis using rats made diabetic by streptozotocin (STZ) injection. The STZ-treated rat is a commonly used animal model of type I diabetes. These rats rapidly develop hyperglycemia and polyuria, although they do not develop ketoacidosis. Because the renal medulla is responsible for the production of concentrated or dilute urine, we hypothesized that any compensatory mechanism to conserve water and solute may involve changes in the abundance of the medullary transport proteins involved in the urinary concentrating mechanism. Therefore, we measured the abundance of the UT-A1 and UT-B urea transporters, the aquaporin-2 (AQP2) water channel, the NKCC2/BSC1 NaϪ cotransporter, and the ROMK K ϩ channel from rats made diabetic for 5, 10, 14, or 20 days. METHODSAnimal preparation. Male Sprague-Dawley rats (Charles River Laboratories, Wilmington, MA) weighing 125-200...

Aldosterone Decreases UT-A1 Urea Transporter Expression via the Mineralocorticoid Receptor

“…We recently showed that UT-A1 protein is upregulated in rats with uncontrolled diabetes at 10 to 20 d after streptozotocin injection (8). We suggested that this upregulation is part of a compensatory response to limit the loss of solute and water despite the ongoing osmotic diuresis (8). During the opposite physiologic condition, aldosterone-induced volume expansion, Wang et al (18) showed that UT-A1 protein abundance is decreased.…”

“…Upregulation of UT-A1 in adrenal insufficiency would tend to blunt the tendency for hemodynamic instability by creating a hypertonic inner medullary interstitium that promotes water reabsorption. We recently showed that UT-A1 protein is upregulated in rats with uncontrolled diabetes at 10 to 20 d after streptozotocin injection (8). We suggested that this upregulation is part of a compensatory response to limit the loss of solute and water despite the ongoing osmotic diuresis (8).…”

“…We previously studied the effect of glucocorticoids (dexamethasone) on UT-A1 protein abundance in adrenalectomized rats. We showed that glucocorticoids decrease the protein abundance of the UT-A1 urea transporter in the inner medullary tip of adrenalectomized rats (6) and in conditions associated with excess glucocorticoid, such as uncontrolled diabetes (7,8). Presumably, in catabolic states in which glucocorticoid levels are increased, UT-A1 is downregulated to permit more nitrogenous waste to be excreted into the urine and to prevent excessive reabsorption of urea across the terminal inner medullary collecting duct (IMCD).…”

X-chromosome linked inhibitor of apoptosis protein inhibits muscle proteolysis in insulin-deficient mice

“…Proteins were subjected to Western blot analysis using previously published methods. 46 Primary antibodies used were anti-XIAP antibody For determination of actin cleavage, hindlimb muscles were pulverized under liquid nitrogen and then homogenized in ice-cold hypotonic buffer. The homogenates were centrifuged (18 000 g for 10 min) and the resulting pellets containing the myofibrils were boiled in Laemmli sample buffer and proteins separated by 15% sodium dodecyl sulfate-polyacrylamide gel electrophoresis.…”

Renal function in a rat model of neurogenic bladder, effect of statins and phosphodiesterase-5 inhibitors

“…It seems that serum creatinine could be a better index of renal function in neurogenic bladder of rats, it reaches normal levels earlier. With regards to bladder weight increase up to eight times in the group with neurogenic bladder and no treatment, and significant body weight decline, it could be concluded that tissue injuries could be due to anatomic disruptions in the urinary system, urine retention and the following glomerular injury [17], leading to abnormal 24 h protein measurements and nitrogen loss at day 28. Bladder hyperplasia (eight times the normal bladder) may be due to neuronal signals causing muscular hypertrophy after spinal injury [18].…”