[Molecular biology in regulation of kidney functions: Kallikrein-kinin system (bradykinin)].
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Animals↗
Biomedical subjects
Shinya Taniguchi
Publications and source records attributed to Shinya Taniguchi.
Proteolipid of vacuolar H(+)-ATPase of Plasmodium falciparum: cDNA cloning, gene organization and complementation of a yeast null mutant.
Vacuolar H(+)-ATPase (V-ATPase), an electrogenic proton pump, is highly expressed in Plasmodium falciparum, the human malaria parasite. Although V-ATPase-driven proton transport is involved in various physiological processes in the parasite, the overall features of the V-ATPase of P. falciparum, including the gene organization and biogenesis, are far less known. Here, we report cDNA cloning of proteolipid subunit c of P. falciparum, the smallest and most highly hydrophobic subunit of V-ATPase. RT-PCR analysis as well as Northern blotting indicated expression of the proteolipid gene in the parasite cells. cDNA, which encodes a complete reading frame comprising 165 amino acids, was obtained, and its deduced amino acid sequence exhibits 52 and 57% similarity to the yeast and human counterparts, respectively. Southern blot analysis suggested the presence of a single copy of the proteolipid gene, with 5 exons and 4 introns. Upon transfection of the cDNA into a yeast null mutant, the cells became able to grow at neutral pH, accompanied by vesicular accumulation of quinacrine. In contrast, a mutated proteolipid with replacement of glutamate residue 138 with glutamine did not lead to recovery of the growth ability or vesicular accumulation of quinacrine. These results indicated that the cDNA actually encodes the proteolipid of P. falciparum and that the proteolipid is functional in yeast.
Amino Acid Substitution↗
QT PRODACT: a multi-site study of in vitro action potential assays on 21 compounds in isolated guinea-pig papillary muscles.
To construct a non-clinical database for drug-induced QT interval prolongation, the electrophysiological effects of 11 positive and 10 negative compounds on action potentials (AP) in guinea-pig papillary muscles were investigated in a multi-site study according to a standard protocol. Compounds with a selective inhibitory effect on the rapidly activated delayed rectifier potassium current (IKr) prolonged action potential duration at 90% repolarization (APD90) in a concentration-dependent manner, those showing Ca2+ current (ICa) inhibition shortened APD30, and those showing Na+ current (INa) inhibition decreased action potential amplitude (APA) and Vmax. Some of the mixed ion-channel blockers showed a bell-shaped concentration-response curve for APD90, probably due to their blockade of INa and/or ICa, sometimes leading to a false-negative result in the assay. In contrast, all positive compounds except for terfenadine and all negative compounds with IKr-blocking activity prolonged APD30-90 regardless of their INa- and/or ICa-blocking activities, suggesting that APD30-90 is a useful parameter for evaluating the IKr-blocking activity of test compounds. Furthermore, the assay is highly informative regarding the modulation of cardiac ion channels by test compounds. Therefore, when APD90 and APD30-90 are both measured, the action potential assay can be considered a useful method for assessing the risk of QT interval prolongation in humans in non-clinical safety pharmacology studies.
Action Potentials↗
QT PRODACT: evaluation of the potential of compounds to cause QT interval prolongation by action potential assays using guinea-pig papillary muscles.
Certain compounds that prolong QT interval in humans have little or no effect on action-potential (AP) duration used traditionally, but they inhibit rapidly-activated-delayed-rectifier potassium currents (IKr) and/or human ether-a-go-go-related gene (hERG) currents. In this study using isolated guinea-pig papillary muscles, we investigated whether new parameters in AP assays can detect the inhibitory effects of various compounds on IKr and/or hERG currents with high sensitivity. The difference in AP duration between 60% and 30% repolarization, 90% and 60% repolarization, and 90% and 30% repolarization (APD30-60, APD60-90, and APD30-90, respectively) were calculated as the new parameters. All the 15 IKr and/or hERG current inhibitors that have been reported (9 compounds) or not reported (6 compounds) to inhibit calcium currents prolonged APD30-60, APD60-90, and/or APD30-90; and 8 of the 15 inhibitors prolonged APD30-60, APD60-90, and/or APD30-90 more potently than APD90. The APD30-60, APD60-90, and APD30-90 measurements revealed no difference in sensitivity when evaluating the effects of the IKr and/or hERG current inhibitors on the three parameters. On the other hand, compounds with little or no effect on hERG currents had no effect on APD30-60, APD60-90, or APD30-90. Therefore, it is concluded that in AP assays using isolated guinea-pig papillary muscles, APD30-60, APD60-90, and APD30-90 are useful indexes for evaluating the inhibitory effects of compounds including mixed ion-channel blockers on IKr and/or hERG currents.
Action Potentials↗