Nitric oxide (NO), among several other functions, may play a role in hypoxia and reoxygenation injury due to its free radical nature and high reactivity with the superoxide radical to yield peroxynitrite, an oxidant molecule. The present study was undertaken to evaluate a potential role for NO, either endogenous or exogenous, in a model of hypoxia/reoxygenation (H/R) in freshly isolated rat proximal tubules. NO synthase activity, as assessed by conversion of L-[3H]arginine to L-[3Hlcitrulline, was detected in normoxic tubules. This activity could be inhibited by N-nitro-L-argin ne methyl ester (L-NAME), a NO synthase inhibitor, and was stimulated by 15 min of hypoxia. The injury in proximal tubules caused by 15 min of hypoxia followed by 35 min of reoxygenation was completely prevented by L-NAME as assessed by release of lactate dehydrogenase, whereas D-NAME, which does not inhibit NO synthase, had no effect. In contrast, L-arginune (NO substrate) enhanced the H/R injury. These effects were paralleled by nitrite/nitrate production. In separate experiments, the addition of sodium nitroprusside, a NO donor, to proximal tubules enhanced the H/R injury; this effect could be blocked by hemoglobin, a NO scavenger. Also, addition of nitroprusside reversed L-NAME protection against H/R injury. These results demonstrate that NO is synthesized in rat proximal tubules and participates as one of the mediators in rat tubular H/R injury.Nitric oxide (NO) is a major chemical form of endotheliumderived relaxing factor (1, 2), an important regulator of vascular tone, and is released by endothelial cells (3). However, the role of NO is not restricted to the vascular system; several other functions have been described in recent years. NO has an important role in platelet function, causing inhibition of platelet aggregation; in immunological reactions, as a host defense mechanism against tumor cells and invasive organisms; and in the central and peripheral nervous systems, as a neurotransmitter (4, 5). Moreover, alterations in NO synthesis have been incriminated in several other pathophysiological conditions, including arterial hypertension and progression of renal failure (6), as well as septic shock (7), hypoxia-induced vasodilation (8), the vasospasm that follows subarachnoid hemorrhage due to inhibition of NO by hemoglobin (9), and neuronal destruction in vascular stroke and other neurodegenerative conditions (10).While endothelial cells, neurons, macrophages, neutrophils, and platelets are well-known sources of NO, recent studies have suggested that epithelial cells may constitutively generate NO (11). Furthermore, constitutive NO synthase (NOS) has been identified in the kidney, specifically in macula densa cells (12) and in the inner medullary collecting duct (13). Recently, the inducible form of NOS was identified in the rat proximal tubule and inner medullary collecting duct (14). In the kidney, NO has an important role in renal hemodynamic regulation and sodium and water excretion (15).The use of freshly isolated ...

Ubiquitin DNA sequences were isolated from the higher plant Arabidopsis thaliana L. by screening a lambda-gt11 genomic library with antibodies raised against oat and human ubiquitin. DNA sequence analysis showed that the predicted protein sequence is 100% conserved with that found in oat and barley and differs by only three residues to that found in animals. This gene (UBQ4) encodes a ubiquitin polyprotein with five repeats contiguously linked with no intervening sequences in the coding region and a C-terminal extension of Ser-Phe. Genomic Southern blot analysis showed that ubiquitin sequences comprise a multigene family of approximately 11 members in Arabidopsis. Northern blot analysis identified at least four transcript size classes, which accumulate in sizes ranging from 800 to 1900 bases. A 5'-specific probe for the UBQ4 gene was used to show that after 2 h heat shock stress, the steady state mRNA level decreased significantly in flowers/buds but not in leaves. The UBQ4 transcript accumulates in a differential manner, accumulating to higher levels in germinating tissue, etiolated tissue, and flowers/buds than in mature leaves, roots, or stems.

Fluorescence polarization technology has been used in basic research and commercial diagnostic assays for many decades, but has begun to be widely used in drug discovery only in the past six years. Originally, FP assays for drug discovery were developed for single-tube analytical instruments, but the technology was rapidly converted to high-throughput screening assays when commercial plate readers with equivalent sensitivity became available. This review will discuss fluorescence polarization assays in current use in drug discovery research as well as those in development that will likely be used in the near future. These assays include targets such as kinases, phosphatases, proteases, G-protein coupled receptors, and nuclear receptors.

Ischemic preconditioning has been shown to ameliorate injury due to subsequent ischemia in several organs. However, relatively little is known about preconditioning and the kidney. To address this, rats were randomized to control (C, N = 14), 2 min of ischemic preconditioning (P2 N = 10), 3 periods of 2 min of ischemia separated by 5 min periods of reflow (P2,3 N = 7), or three 5 min periods of ischemia separated by 5 min of reflow (P5,3 N = 6) prior to 45 min of bilateral renal ischemia followed by 24 hours of reperfusion. We observed a lower serum creatinine after 24 hours of reflow in P2, P2, 3 but not P5, 3 rats compared with C. Histology was examined in the C and P2, 3 groups and demonstrated less severe injury in the P2, 3 group. To gain insight into the mechanism by which preconditioning ameliorated ischemic injury, we performed near IR spectroscopy and 31P NMR spectroscopy. Based on near IR spectroscopy, the P2, 3 group had closer coupling of cytochrome aa3 redox state with that of hemoglobin during reflow. In the 31P NMR studies, the changes in ATP and pHi were similar during ischemia, but the P2, 3 group recovered ATP and pHi faster than C. These data suggest that ischemic preconditioning may ameliorate ischemic renal injury as assessed by functional, metabolic and morphological methods. The mechanism(s) by which this occurs requires additional study.

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The pathogenetic factors involved in norepinephrine- (NE) induced reversible acute renal failure (ARF) were examined in untreated (U) and mannitol-treated (M) animals. At 3 and 24 h after NE infusion renal blood flow (RBF) was significantly higher in M compared to U animals (174 vs. 138 and 191 vs. 148 ml/min, respectively, both P less than 0.05). At 3 h, glomerular filtration rate (GFR) was higher in M animals (8 vs. 4 ml/min, P less than 0.01), while at 24 h protection was even greater (18 vs. 3 ml/min, P less than 0.01). In U animals proximal tubule pressure (Pt) was lower at 1 h than before NE (13 vs. 23 mmHg, P less than 0.01); from 1 to 3 h Pt increased to elevated levels in parallel with restoration of RBF (r = 0.62, P less than 0.01). At 3 h in U animals stop-flow pressure (SFP), as an index of glomerular capillary pressure, was below normal (35 vs. 44 mmHg, P less than 0.05) yet Pt was increased (35 vs. 23 mmHg, P less than 0.05). Thus little transglomerular pressure gradient was present for ultrafiltration. Further evidence of tubular obstruction was obtained by microperfusion at 6 nl/min, which increased Pt from 30 to 45 mmHg (P less than 0.001), a finding not present in unobstructed tubules. Delayed excretion (approximately 20 min) of microinjected [3H]inulin also was compatible with renal ischemia and tubule obstruction. Microinjection studies provided no evidence for backleak of tubular fluid. At 1 h, Pt was higher in M vs. U animals (31 vs. 13 mmHg, P less than 0.05). In M animals at 3 h SFP was normal (50 vs. 44 mmHg) and Pt was below SFP (32 vs. 50 mmHg, P less than 0.01), thus preserving a substantial transglomerular pressure gradient for ultrafiltration. In summary, reduced GFR in U animals is characterized by a combination of reduced glomerular capillary pressure and tubule obstruction. In contrast, animals receiving mannitol were protected against ARF through maintenance of glomerular capillary pressure and prevention of tubular obstruction, perhaps by increasing Pt within the first hour of the NE insult.

The role of the lysosomal proteases cathepsins B and L and the calcium-dependent cytosolic protease calpain in hypoxia-induced renal proximal tubular injury was investigated. As compared to normoxic tubules, cathepsin B and L activity, evaluated by the specific fluorescent substrate benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methylcoumarin, was not increased in hypoxic tubules or the medium used for incubation of hypoxic tubules in spite of high lactate dehydrogenase (LDH) release into the medium during hypoxia. These data in rat proximal tubules suggest that cathepsins are not released from lysosomes and do not gain access to the medium during hypoxia. An assay for calpain activity in isolated proximal tubules using the fluorescent substrate N-succinyl-Leu-Tyr-7-amido-4-methylcoumarin was developed. The calcium ionophore ionomycin induced a dose-dependent increase in calpain activity. This increase in calpain activity occurred prior to cell membrane damage as assessed by LDH release. Tubular calpain activity increased signifi'cantly by 7.5 min of hypoxia, before there was significant LDH release, and further increased during 20 min of hypoxia. The cysteine protease inhibitor N-benzyloxycarbonyl-Val-Phe methyl ester (CBZ) markedly decreased LDH release after 20 min of hypoxia and completely prevented the increase in calpain activity during hypoxia. The increase in calpain activity during hypoxia and the inhibitor studies with CBZ therefore supported a role for calpain as a mediator of hypoxia-induced proximal tubular injury.The mechanisms responsible for hypoxia-induced tubular epithelial cell injury and death are controversial (1). Intracellular calcium has been suggested to be important in mediation of this hypoxic injury in renal proximal tubules (2). Our laboratory recently reported that cytosolic free Ca2+ [(Ca2+)i] is significantly increased by 2 min of hypoxia in proximal tubules, and that (Ca2+)i levels at 10 min of hypoxia correlated with subsequent damage at 20 min (3). Thus, prompt increases in (Ca2+), may play an initiating role in hypoxic injury. This conclusion was supported by the protection afforded by prevention of the increase in (Ca2+), (3,4). The mechanisms whereby increases in (Ca2+), lead to cell membrane injury, however, remain to be defined. An increase in (Ca2+)i may activate calcium-dependent enzymes, which could provide a mechanism for cell injury. The increase in (Ca2+)i during hypoxia may activate phospholipase A2 and thus be partly responsible for phospholipid degradation in membranes observed during hypoxia (5). Another potential mechanism for calcium-dependent cell injury is activation of the calciumdependent cytosolic protease calpain. In certain circumstances, proteases have been shown to play a role in cellular injury. For example, studies with cultured fibroblasts and the specific lysosomotropic detergent C12-imidazole demonstrated that cell killing can be caused by activation and/or release into the cytoplasm of cysteine proteases (6). Studies of cysteine p...

Forty-nine consecutive subjects with established diabetic peripheral neuropathy were treated with monochromatic near-infrared photo energy (MIRE) to determine if there was an improvement of sensation. Loss of protective sensation characterized by Semmes-Weinstein monofilament values of 4.56 and above was present in 100% of subjects (range, 4.56 to 6.45), and 42 subjects (86%) had Semmes-Weinstein values of 5.07 or higher. The ability to discriminate between hot and cold sensation was absent (54%) or impaired (46%) in both groups prior to the initiation of MIRE treatment. On the basis of Semmes-Weinstein monofilament values, 48 subjects (98%) exhibited improved sensation after 6 treatments, and all subjects had improved sensation after 12 treatments. Therefore, MIRE may be a safe, drug-free, noninvasive treatment for the consistent and predictable improvement of sensation in diabetic patients with peripheral neuropathy of the feet.