adenosine-5--o-(3-thiotriphosphate) and Disease-Models--Animal

AVP resistance of the medullary collecting duct (mCD) in postobstructive uropathy (POU) has been attributed to increased production of PGE2. P2Y2 receptor activation causes production of PGE2 by the mCD. We hypothesize that increased P2Y2 receptor expression and/or activity may contribute to the diuresis of POU. Sprague-Dawley rats were subjected to bilateral ureteral obstruction for 24 h followed by release (BUO/R, n = 17) or sham operation (SHM/O, n = 15) and euthanized after 1 wk or 12 days. BUO/R rats developed significant polydipsia, polyuria, urinary concentration defect, and increased urinary PGE2 and decreased aquaporin-2 protein abundance in the inner medulla compared with SHM/O rats. After BUO/R, the relative mRNA expression of P2Y2 and P2Y6 receptors was increased by 2.7- and 4.9-fold, respectively, without significant changes in mRNA expression of P2Y1 or P2Y4 receptor. This was associated with a significant 3.5-fold higher protein abundance of the P2Y2 receptor in BUO/R than SHM/O rats. When freshly isolated mCD fractions were challenged with different types of nucleotides (ATPgammaS, ADP, UTP, or UDP), BUO/R and SHM/O rats responded to only ATPgammaS and UTP and released PGE2, consistent with involvement of the P2Y2, but not P2Y6, receptor. ATPgammaS- or UTP-stimulated increases in PGE2 were much higher in BUO/R (3.20- and 2.28-fold, respectively, vs. vehicle controls) than SHM/O (1.68- and 1.30-fold, respectively, vs. vehicle controls) rats. In addition, there were significant 2.4- and 2.1-fold increases in relative mRNA expression of prostanoid EP1 and EP3 receptors, respectively, in the inner medulla of BUO/R vs. SHM/O rats. Taken together, these data suggest that increased production of PGE2 by the mCD in POU may be due to increased expression and activity of the P2Y2 receptor. Increased mRNA expression of EP1 and EP3 receptors in POU may also help accentuate PGE2-induced signaling in the mCD.

Topics: Adenosine Triphosphate; Animals; Dinoprostone; Disease Models, Animal; Diuresis; Gene Expression Regulation; Kidney Concentrating Ability; Kidney Tubules, Collecting; Male; Polyuria; Purinergic P2 Receptor Agonists; Rats; Rats, Sprague-Dawley; Receptors, Prostaglandin E; Receptors, Prostaglandin E, EP1 Subtype; Receptors, Prostaglandin E, EP3 Subtype; Receptors, Purinergic P2; Receptors, Purinergic P2Y2; RNA, Messenger; Signal Transduction; Time Factors; Up-Regulation; Ureteral Obstruction; Uridine Triphosphate

ATP stimulation of purinergic P2 receptors (P2YR and P2XR) regulates several hepatic functions. Here we report the involvement of ATP-mediated signals in enhancing hepatocyte tolerance to lethal stress.. The protection given by purinergic agonists was investigated in rat hepatocytes exposed to hypoxia.. ATP released after hypotonic stress (200 mOsm/L) as well as P2YR agonists prevented hepatocyte killing by hypoxia with efficiency ranking UTP > ATPgammaS > ADPbetaS, whereas the P2XR agonist, methylene-adenosine-5'-triphosphate, was ineffective. Adenosine-5'-O-3-thiotriphosphate (ATPgammaS; 100 micromol/L) also prevented Na+ -overload in hypoxic cells by inhibiting the Na+/H+ exchanger, without interfering with hypoxic acidosis. ATPgammaS activated Src and promoted a Src-dependent stimulation of both ERK1/2 and p38MAPK. Blocking p38MAPK with SB203580 reverted the protection given by ATPgammaS on both cell viability and Na+ accumulation, whereas ERK1/2 inhibition with PD98058 was ineffective. An increased phosphorylation of ERK1/2 was also evident in untreated hypoxic hepatocytes. PD98058 ameliorated Na+ accumulation and cell death caused by hypoxia. Hepatocyte pre-treatment with ATPgammaS reverted ERK1/2 activation in hypoxic cells. SB203580 blocked the effects of ATPgammaS on both ERK1/2 and Na+/H+ exchanger.. The activation of p38MAPK by P2Y2R increases hepatocyte resistance to hypoxia by down-modulating ERK1/2-mediated signals that promote Na+ influx through the Na+/H+ exchanger.

Topics: Adenosine Triphosphate; Affinity Labels; Animals; Cell Death; Disease Models, Animal; Hepatocytes; Hypoxia; Male; Organic Chemicals; Rats; Rats, Wistar; Receptors, Purinergic P2; Receptors, Purinergic P2Y2; Reperfusion Injury; Signal Transduction; Sodium

The mechanisms responsible for acute renal failure in sepsis are not understood. Measurement of tissue ATP might help to understand this process but, in the large animal, it is hampered by major technical difficulties.. To develop a technique to monitor ATP in the kidney of a large mammal during the induction of septic shock and then circulatory arrest.. Implantation of a custom-made phosphorus coil around the left kidney. Induction of septic shock by intravenous E. coli administration. Acquisition of 31 P magnetic resonance (MR) spectroscopic data at 3-tesla before and during septic shock over several hours. Induction of euthanasia and measurement of the same 31 P signal immediately and thirty minutes after circulatory arrest.. Clear reproducible 31 P MR spectra were obtained before and after the induction of septic shock and euthanasia. They indicated limited changes in ATP during septic shock. An expected rapid and dramatic decrease in ATP occurred with euthanasia.. It is possible to sequentially monitor renal bioenergetics in a large mammal during septic shock using an implanted custom-made phosphorus coil and 3-tesla MR technology. This technique offers a novel approach to the investigation of septic renal failure.

Topics: Acute Kidney Injury; Adenosine Triphosphate; Animals; Bacteremia; Disease Models, Animal; Escherichia coli Infections; Female; Kidney; Magnetic Resonance Spectroscopy; Phosphocreatine; Phosphorus Isotopes; Sheep; Shock; Shock, Septic; Thionucleotides

Spectral analysis of electrical noise recorded from the round window (RW) of the cochlea is referred to as the ensemble spontaneous activity (ESA) of the cochlear nerve. The ESA is considered to represent the summed spontaneous activity of single fibers of the auditory nerve and changes in the spectral characteristics of the ESA have been observed in humans with tinnitus. Experiments were undertaken to determine the relationship of the ESA to auditory neurotransmission. The ESA consisted of energy centered at approximately 900 Hz, similar to the spectral peak of single auditory neuron discharges. The amplitude of the ESA was correlated with good auditory sensitivity in the 12-30 kHz region of the cochlea. Constant pure tones of 12-22 kHz suppressed the ESA reducing its amplitude in a frequency and intensity dependent manner implying that the ESA recorded at the RW is generated or dominated by neurons in the basal region of the cochlea. The ESA was significantly suppressed by round window perfusion of the P2X receptor agonist adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) (10 mM) the glutamate receptor antagonist 6-7-dinitroquinoxaline-2,3-dione (DNQX) (1 mM), and the sodium channel antagonist tetrodotoxin (TTX) (20 microM). Following intravenous furosemide injection (40 mg/kg) reduction and recovery of the ESA correlated with similar changes in the endocochlear potential (EP). Following DNQX and ATPgammaS an additional spectral peak at 200 Hz was often observed. This peak has been postulated to be a correlate of tinnitus in humans but had not previously been observed in a guinea-pig model of tinnitus. These data confirm the spectral characteristics of the ESA in guinea-pigs and show it is dependent on the sensitivity of the auditory nerve and intact auditory neurotransmission. In addition these experiments support the view that the ESA represents summed spontaneous neural activity in the cochlea and provide a platform for studies of the influence of ototoxic compounds on the spontaneous neural outflow of the cochlea as a model of tinnitus.

Topics: Acoustic Stimulation; Adenosine Triphosphate; Animals; Cochlear Nerve; Disease Models, Animal; Electrophysiology; Excitatory Amino Acid Antagonists; Female; Furosemide; Guinea Pigs; Humans; Male; Nerve Fibers; Purinergic P2 Receptor Agonists; Quinoxalines; Receptors, Purinergic P2X; Sodium Channel Blockers; Synaptic Transmission; Tetrodotoxin; Tinnitus