The Cell Biology of Gastric Acid Secretion

Okamoto, Curtis T.; Asano, Shinji; Sakai, Hideki

doi:10.1016/b978-0-12-809954-4.00038-4

Cited by 3 publications

(2 citation statements)

References 333 publications

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“…As intestinal stems cells are intrinsically programmed with their location-specific functions [ 17 ], organoids derived from different regions of the gastrointestinal tract retain the unique properties of their site of origin, enabling a new dimension of spatial resolution in research, not covered previously by cell lines. Also the pH varies greatly along the gastrointestinal tract, increasing from pH 1.2 in the empty stomach, pH 5–7 in the small intestine, to 6–7.5 in the colon [ 18 ]. Digestion starts in the oral cavity with salivary amylase and continuous in the stomach, however, the small intestine is the major site for both digestion and absorption [ 19 ].…”

Section: Bioavailability and The Intestinal Epitheliummentioning

confidence: 99%

Drug Screening, Oral Bioavailability and Regulatory Aspects: A Need for Human Organoids

Zietek

Boomgaarden²,

Rath

2021

Pharmaceutics

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The intestinal epithelium critically contributes to oral bioavailability of drugs by constituting an important site for drug absorption and metabolism. In particular, intestinal epithelial cells (IEC) actively serve as gatekeepers of drug and nutrient availability. IECs’ transport processes and metabolism are interrelated to the whole-body metabolic state and represent potential points of origin as well as therapeutic targets for a variety of diseases. Human intestinal organoids represent a superior model of the intestinal epithelium, overcoming limitations of currently used in vitro models. Caco2 cells or rodent explant models face drawbacks such as their cancer and non-human origin, respectively, but are commonly used to study intestinal nutrient absorption, enterocyte metabolism and oral drug bioavailability, despite poorly correlative data. In contrast, intestinal organoids allow investigating distinct aspects of bioavailability including spatial resolution of transport, inter-individual differences and high-throughput screenings. As several countries have already developed strategic roadmaps to phase out animal experiments for regulatory purposes, intestinal organoid culture and organ-on-a-chip technology in combination with in silico approaches are roads to go in the preclinical and regulatory setup and will aid implementing the 3Rs (reduction, refinement and replacement) principle in basic science.

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Section: Bioavailability and The Intestinal Epitheliummentioning

confidence: 99%

Drug Screening, Oral Bioavailability and Regulatory Aspects: A Need for Human Organoids

Zietek

Boomgaarden²,

Rath

2021

Pharmaceutics

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show abstract

“…However, their cation selectivity and transport stoichiometry need to be very specific in order to achieve their respective physiological roles. HKA acidifies gastric juice down to pH1, which corresponds to a more than one million-fold H + gradient, one of the highest gradients known in mammalian tissue (12,13). Therefore, because of the limited free energy available from ATP hydrolysis, the stoichiometry of transported cations needs to be strictly 1H + /1K + per ATP to satisfy the thermodynamic requirement (14)(15)(16).…”

Section: Introductionmentioning

confidence: 99%

Gastric proton pump with two occluded K+ engineered with sodium pump-mimetic mutations

Abe

Yamamoto

Irie

et al. 2021

Preprint

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The gastric H+,K+-ATPase mediates electroneutral exchange of 1H+/1K+ per ATP hydrolysed across the membrane. Previous structural analysis of the K+-occluded E2-Pi form of H+,K+-ATPase showed a single bound K+ at cation-binding site II, in marked contrast to the two K+ occluded at sites I and II of the closely-related Na+,K+-ATPase which mediates electrogenic 3Na+/2K+ translocation across the membrane. The two pumps show significant differences in structure in and around Site I, but which are critical for blocking K+ binding in the gastric pump and contribute to binding in the sodium pump is unclear. We have a series of crystal structures and a cryo-EM structure of H+,K+-ATPase mutants with changes in the vicinity of site I based on the structure of the sodium pump. The number of bound Rb+, determined by its anomalous dispersion, remains one in the luminal-open E2BeF form of the Lys791Ser single mutant and Lys791Ser/Glu820Asp double mutant, mutation that could create space and may directly bind the cation. We next introduced mutations in peripheral residues Try340Asn and Glu936Val. A strong and spread-out Rb+ anomalous density observed in the quadruple mutant suggests that a certain population ATPases has two Rb+ bound. We then added gate-closing mutation Try799Trp and determined its cryo-EM structure in the occluded E2-AlF form. This quintuple mutant unambiguously has two separate densities at the cation-binding site. The step-wise construction of the K+ binding site offers new insight into how it is blocked in the one pump and constituted in the other.

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Gastric proton pump with two occluded K+ engineered with sodium pump-mimetic mutations

et al. 2021

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The gastric H+,K+-ATPase mediates electroneutral exchange of 1H+/1K+ per ATP hydrolysed across the membrane. Previous structural analysis of the K+-occluded E2-P transition state of H+,K+-ATPase showed a single bound K+ at cation-binding site II, in marked contrast to the two K+ ions occluded at sites I and II of the closely-related Na+,K+-ATPase which mediates electrogenic 3Na+/2K+ translocation across the membrane. The molecular basis of the different K+ stoichiometry between these K+-counter-transporting pumps is elusive. We show a series of crystal structures and a cryo-EM structure of H+,K+-ATPase mutants with changes in the vicinity of site I, based on the structure of the sodium pump. Our step-wise and tailored construction of the mutants finally gave a two-K+ bound H+,K+-ATPase, achieved by five mutations, including amino acids directly coordinating K+ (Lys791Ser, Glu820Asp), indirectly contributing to cation-binding site formation (Tyr340Asn, Glu936Val), and allosterically stabilizing K+-occluded conformation (Tyr799Trp). This quintuple mutant in the K+-occluded E2-P state unambiguously shows two separate densities at the cation-binding site in its 2.6 Å resolution cryo-EM structure. These results offer new insights into how two closely-related cation pumps specify the number of K+ accommodated at their cation-binding site.

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The Cell Biology of Gastric Acid Secretion

Cited by 3 publications

References 333 publications

Drug Screening, Oral Bioavailability and Regulatory Aspects: A Need for Human Organoids

Drug Screening, Oral Bioavailability and Regulatory Aspects: A Need for Human Organoids

Gastric proton pump with two occluded K+ engineered with sodium pump-mimetic mutations

Gastric proton pump with two occluded K+ engineered with sodium pump-mimetic mutations

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