title: High rates of intestinal bicarbonate secretion in seawater tilapia (Oreochromis mossambicus).
abstract: Osmoregulation in fish is a complex process that requires the orchestrated cooperation of many tissues. In fish facing hyperosmotic environments, the intestinal absorption of some monovalent ions and the secretion of bicarbonate are key processes to favor water absorption. In the present study, we showed that bicarbonate levels in the intestinal fluid are several fold higher in seawater than in freshwater acclimated tilapia (Oreochromis mossambicus). In addition, we analyzed gene expression of the main molecular mechanisms involved in HCO3-movements i.e. slc26a6, slc26a3, slc4a4 and v-type H-ATPase sub C in the intestine of tilapia acclimated to both seawater and freshwater. Our results show an anterior/posterior functional regionalization of the intestine in tilapia in terms of expression patterns, which is affected by environmental salinity mostly in the anterior and mid intestine. Analysis of bicarbonate secretion using pH-Stat in tissues mounted in Ussing chambers reveals high rates of bicarbonate secretion in tilapia acclimated to seawater from anterior intestine to rectum ranging between ~900 and ~1700nmolHCO3-cm-2h-1. However, a relationship between the expression of slc26a6, slc26a3, slc4a4 and the rate of bicarbonate secretion seems to be compromised in the rectum. In this region, the low expression of the bicarbonate transporters could not explain the high bicarbonate secretion rates here described. However, we postulate that the elevated v-type H-ATPase mRNA expression in the rectum could be involved in this process.
authors.affiliation: Comparative Endocrinology and Integrative Biology, Centre of Marine Sciences (CCMar), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: I
authors.initials: I
authors.lastname: Ruiz-Jarabo
authors.affiliation: Comparative Endocrinology and Integrative Biology, Centre of Marine Sciences (CCMar), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: S F
authors.initials: SF
authors.lastname: Gregório
authors.affiliation: Comparative Endocrinology and Integrative Biology, Centre of Marine Sciences (CCMar), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Università degli Studi di Messina, Messina, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Gaetano
authors.affiliation: Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Università degli Studi di Messina, Messina, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Trischitta
authors.affiliation: Comparative Endocrinology and Integrative Biology, Centre of Marine Sciences (CCMar), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal. Electronic address: jfuentes@ualg.pt.
authors.forename: J
authors.initials: J
authors.lastname: Fuentes
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D005880:Gills / Q000378:metabolism* / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism*; D017136:Ion Transport / Q000235:genetics / Q000502:physiology; D064587:Osmoregulation / Q000235:genetics; D006180:Proton-Translocating ATPases; D054712:Salinity; D012623:Seawater; D000254:Sodium-Potassium-Exchanging ATPase; D017210:Tilapia / Q000235:genetics / Q000378:metabolism*; D014882:Water-Electrolyte Balance
chemical_list: D001639:Bicarbonates; D006180:Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Bicarbonate secretion; Intestine; Ion transport; Oreochromis mossambicus; Osmoregulation