Nce of detecting changes in renal function at an early stage. However, the identification of urinary proteins that are directly derived from the kidney is required. To the best of our knowledge, there have been no studies that directly and comprehensively identified proteins of kidney origin in urine. An analysis of kidney origin proteins in urine should exclude proteins present in urine as the result of the ultrafiltration of plasma. Isolated kidney perfusion is a classic technique that has been widely used for the study of renal physiology, pharmacology, and pharmacokinetics [10]. A perfused isolated kidney can maintain approximately normal physiological functions for more than two hours when it is circularly perfused with artificial bloodfree perfusion fluids, such as buffered saline solutions supplemented with macromolecular plasma substitutes [10]. In this study, we used a modified isolated rat kidney perfusion model to analyze the kidney origin proteins present in the urinary tract.Identifying Kidney Origin Proteins in UrineExperimental Procedures Ethics Title Loaded From File StatementThis study was approved by the Institute of Basic Medical Sciences Animal Ethics Committee, Peking Union Medical College (Animal Welfare Assurance Number: A5518). Male Sprague-Dawley rats (350?50 g) from the Institute of Laboratory Animal Science were maintained at approximately 21uC on a 12 h light/dark cycle with free access to food and water.Perfusate PreparationModified Krebs-Henseleit buffer (4.7 mM KCl, 1.2 mM KH2PO4, 2.1 mM MgSO4, 117 mM NaCl, 25 mM NaHCO3, 2.5 mM CaCl2, 11 g/L glucose) was used as a perfusate with 60 g/L clinical grade dextran added as an oncotic agent [11]. Twenty amino acids were combined in solution to achieve the following concentrations: 2 mM alanine, 0.5 mM arginine, 0.2 mM asparagine, 0.2 mM aspartate, 0.5 mM cysteine, 0.5 mM glutamate, 2 mM glutamine, 2.3 mM glycine, 0.24 mM histidine, 0.3 mM isoleucine, 0.4 mM leucine, 1 mM lysine, 0.33 mM methionine, 0.32 mM phenylalanine, 0.31 mM proline, 1 mM serine, 0.24 mM threonine, 0.07 mM tryptophan, 0.2 mM tyrosine, and 0.33 mM valine [12]. The perfusate was filtered through a 0.45 mm filter and equilibrated with a mixture of oxygen and carbon dioxide (95 O2/5 CO2) for at least two hours prior to use. The perfusate was used within 23148522 six hours of preparation, and the pH of the solution was adjusted to 7.4 with hydrochloric acid prior to use.perfusates and perfusion-driven urine was centrifuged at 12,0006g for 10 min at 4uC to determine if there were red blood cells in the perfusates, and the cell debris in the perfusion-driven urine was evaluated by macroscopic observation. Only isolated perfused kidneys that were negative for both of the above inspections were considered to be successful preparations and proceeded to the next stage. In the next stage, another 300 ml of fresh perfusion medium was used to perfuse the kidney for another 40 min under the same conditions, except that the perfusion medium was not supplemented with oxygen. The perfusion pressure and flow rate were recorded at 10-minute intervals over both stages of the Ves were generated by a cycle of 95uC for 1 min, 65uC experiments. When the experiment was complete, the perfusion-driven urine with and without oxygen supplementation was collected and prepared for analysis.Preparation of Proteins in Perfusion-driven UrineSDS-PAGE separation for the comprehensive analysis of the perfusion-driven urine with oxygen supplementation. To identify proteins in urine that werecollected during perfu.Nce of detecting changes in renal function at an early stage. However, the identification of urinary proteins that are directly derived from the kidney is required. To the best of our knowledge, there have been no studies that directly and comprehensively identified proteins of kidney origin in urine. An analysis of kidney origin proteins in urine should exclude proteins present in urine as the result of the ultrafiltration of plasma. Isolated kidney perfusion is a classic technique that has been widely used for the study of renal physiology, pharmacology, and pharmacokinetics [10]. A perfused isolated kidney can maintain approximately normal physiological functions for more than two hours when it is circularly perfused with artificial bloodfree perfusion fluids, such as buffered saline solutions supplemented with macromolecular plasma substitutes [10]. In this study, we used a modified isolated rat kidney perfusion model to analyze the kidney origin proteins present in the urinary tract.Identifying Kidney Origin Proteins in UrineExperimental Procedures Ethics StatementThis study was approved by the Institute of Basic Medical Sciences Animal Ethics Committee, Peking Union Medical College (Animal Welfare Assurance Number: A5518). Male Sprague-Dawley rats (350?50 g) from the Institute of Laboratory Animal Science were maintained at approximately 21uC on a 12 h light/dark cycle with free access to food and water.Perfusate PreparationModified Krebs-Henseleit buffer (4.7 mM KCl, 1.2 mM KH2PO4, 2.1 mM MgSO4, 117 mM NaCl, 25 mM NaHCO3, 2.5 mM CaCl2, 11 g/L glucose) was used as a perfusate with 60 g/L clinical grade dextran added as an oncotic agent [11]. Twenty amino acids were combined in solution to achieve the following concentrations: 2 mM alanine, 0.5 mM arginine, 0.2 mM asparagine, 0.2 mM aspartate, 0.5 mM cysteine, 0.5 mM glutamate, 2 mM glutamine, 2.3 mM glycine, 0.24 mM histidine, 0.3 mM isoleucine, 0.4 mM leucine, 1 mM lysine, 0.33 mM methionine, 0.32 mM phenylalanine, 0.31 mM proline, 1 mM serine, 0.24 mM threonine, 0.07 mM tryptophan, 0.2 mM tyrosine, and 0.33 mM valine [12]. The perfusate was filtered through a 0.45 mm filter and equilibrated with a mixture of oxygen and carbon dioxide (95 O2/5 CO2) for at least two hours prior to use. The perfusate was used within 23148522 six hours of preparation, and the pH of the solution was adjusted to 7.4 with hydrochloric acid prior to use.perfusates and perfusion-driven urine was centrifuged at 12,0006g for 10 min at 4uC to determine if there were red blood cells in the perfusates, and the cell debris in the perfusion-driven urine was evaluated by macroscopic observation. Only isolated perfused kidneys that were negative for both of the above inspections were considered to be successful preparations and proceeded to the next stage. In the next stage, another 300 ml of fresh perfusion medium was used to perfuse the kidney for another 40 min under the same conditions, except that the perfusion medium was not supplemented with oxygen. The perfusion pressure and flow rate were recorded at 10-minute intervals over both stages of the experiments. When the experiment was complete, the perfusion-driven urine with and without oxygen supplementation was collected and prepared for analysis.Preparation of Proteins in Perfusion-driven UrineSDS-PAGE separation for the comprehensive analysis of the perfusion-driven urine with oxygen supplementation. To identify proteins in urine that werecollected during perfu.