1989 Fiscal Year Final Research Report Summary
Function mechanisms of cation-driven carriers in transporting epithelia
| Project/Area Number |
62480101
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
General physiology
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| Research Institution | University of Shizuoka |
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Principal Investigator |
HOSHI Takeshi University of Shizuoka, School of Food & Nutritional Sciences Professor, 食品栄養科学部, 教授 (60004537)
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| Co-Investigator(Kenkyū-buntansha) |
GODA Toshinao University of Shizuoka, School of Food & Nutritional Sciences Assistant, 食品栄養科学部, 助手 (70195923)
FUJITA Teruyuki University of Shizuoka, School of Food & Nutritional Sciences Professor, 食品栄養科学部, 教授 (20013302)
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| Project Period (FY) |
1987 – 1989
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| Keywords | Cation-driven Carriers / H^+ / peptide Cotransport / Stoichiometry / Proton Gradient Formation / Intestinal Brush Border Membrane / Basic Amino Acid Transport / Na^+-dependent Process / Renal Proximal Tubule |
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| Research Abstract |
This work aimed at clarification of mechanisms of cation-driven carrier transport of nutrients across intestine and renal tubular epithelia. Three major problems were specifically investigated during this period: (1) stoichiometry and specificity of the H^+/Peptide cotransport. (2) nature of the H^+ gradient which drives the H^+ cotransport, (3) localization of Na^+-dependent step of active transepithelial transport of basic amino acid, Reading problem (1). simultaneous measurements of short-circuit current increase and Gly-Gly influx across overted intestine gave the stoichiometry of 2:1 for H^+/Gly-Gly cotransport. All glycyl- and alanyl-dipeptides tested were found to be transported by a common carrier at the same stoichiometry.
In regard to (2). intracellular pH of enterocytes as determined by digitonin equilibration method was found to be 7.10-7.15, whereas the cell surface pH as measured with ph-sensitive microelectrodes was around 6.0. Thus, a pH gradient about 1 pH unit is normally maintained across the luminal membranes.
Both pHi and the cell surface pH were strongly sensitive to amiloride. indicating tertiary active nature of H^+/peptide cotransport. Reading (3). dependence of lysine- induced cell membrane depolarization on intraluminal Na^+ and H^+ and on peritubular Na^+ was studied in Triturus proximal tubule, No immediate effect of intraluminal Na^+ or H^+ was found, but the lack of peritubular Na^+ caused gradual decay of electrical responsiveness to intraluminally applied lysine. Addition of Na^+ to the peritubular side restored the responsiveness rapidly, Na^+ influx across the peritubular membrane was much greater in lysine-loaded cells than in unloaded cells, indicating the presence of a Na^+/lysine exchange mechanism in the peritubular membrane. Thus the Na^+-driven step could clearly localized in the proximal tubule for active transepithelial transport of basic amino acids.
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