Evolution of extreme stomach pH in bilateria inferred from gastric alkalization mechanisms in basal deuterostomes

Stumpp, Meike, Hu, Marian Yong-An, Tseng, Yung-Che, Guh, Ying-Jeh, Chen, Yi-Chih, Yu, Jr-Kai, Su, Yi-Hsien and Hwang, Pung-Pung (2015) Evolution of extreme stomach pH in bilateria inferred from gastric alkalization mechanisms in basal deuterostomes Scientific Reports, 5 (10421). DOI 10.1038/srep10421.

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Abstract

The stomachs of most vertebrates operate at an acidic pH of 2 generated by the gastric H+/K+-ATPase located in parietal cells. The acidic pH in stomachs of vertebrates is believed to aid digestion and to protect against environmental pathogens. Little attention has been placed on whether acidic gastric pH regulation is a vertebrate character or a deuterostome ancestral trait. Here, we report alkaline conditions up to pH 10.5 in the larval digestive systems of ambulacraria (echinoderm + hemichordate), the closest relative of the chordate. Microelectrode measurements in combination with specific inhibitors for acid-base transporters and ion pumps demonstrated that the gastric alkalization machinery in sea urchin larvae is mainly based on direct H+ secretion from the stomach lumen and involves a conserved set of ion pumps and transporters. Hemichordate larvae additionally utilized HCO 3- transport pathways to generate even more alkaline digestive conditions. Molecular analyses in combination with acidification experiments supported these findings and identified genes coding for ion pumps energizing gastric alkalization. Given that insect larval guts were also reported to be alkaline, our discovery raises the hypothesis that the bilaterian ancestor utilized alkaline digestive system while the vertebrate lineage has evolved a strategy to strongly acidify their stomachs.

Document Type: Article
Additional Information: WOS:000356062500001
Keywords: ACID-SECRETION; EXPRESSION PATTERNS; K+/H+ ANTIPORT; CARBONIC-ACID; H+/K+-ATPASE; BETA-SUBUNIT; H+-ATPASE; LARVAL; SEAWATER; DISSOCIATION
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence > FO-R08
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-B Experimental Ecology - Benthic Ecology
OceanRep > The Future Ocean - Cluster of Excellence > FO-R03
OceanRep > The Future Ocean - Cluster of Excellence > FO-R04
Refereed: Yes
DOI etc.: 10.1038/srep10421
ISSN: 2045-2322
Projects: Future Ocean
Date Deposited: 25 Jun 2015 10:06
Last Modified: 19 Dec 2017 12:42
URI: http://eprints.uni-kiel.de/id/eprint/29058

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