title: Low pH and calcium effects on net Na+ and K+ fluxes in two catfish species from the Amazon River (Corydoras: Callichthyidae).
abstract: The present study analyzes Na+ and K+ disturbances caused by low pH in two catfish species from the Amazon River. Corydoras adolfoi inhabits ion-poor, black-stained, low pH (3.5-4.0) waters, while C. schwartzi is native to ion-rich waters at circumneutral pH. Fish were exposed to pH 3.5 Ca2+-free, and Ca2+-enriched (approximately 500 micromol/l) water to determine the protective effects of calcium. Net Na+ and K+ fluxes were measured in the water collected from the fish experimental chambers. C. adolfoi was unable to control the Na+ efflux at low pH, exhibiting Na+ loss up to -594 +/- 84 nmol g(-1) h(-1) during the first hour. After 3 and 6 h, net Na+ flux increased by 7- and 23-fold, respectively. In C. schwartzi, at pH 3.5, the initial high Na+ loss (-1,063 +/- 73 nmol g(-1) h(-1)) was gradually attenuated. A K+ loss occurred in both species, but remained relatively constant throughout exposure. High [Ca2+] affected ion losses in both species. C. adolfoi had 70% loss attenuation, indicating incapacity to control Na+ efflux. In C. schwartzi, elevated [Ca2+] completely prevented the Na+ losses caused by exposure to low pH. Rather different patterns were seen for K+ fluxes, with C. adolfoi showing no K+ disruption when exposed to low pH/high [Ca2+]. Thus, C. adolfoi loses Na+ during acid exposure, but has the ability to control K+ loss, while C. schwartzi controls diffusive Na+ loss but exhibits a slightly higher K+ loss. Ion balance was influenced by [Ca2+] at low pH in C. schwartzi but not in C. adolfoi.
authors.affiliation: Laboratório de Ecofisiologia e Evolução Molecular, Instituto Nacional de Pesquisa da Amazônia, Manaus, AM, Brasil.
authors.forename: A Y
authors.initials: AY
authors.lastname: Matsuo
authors.forename: A L
authors.initials: AL
authors.lastname: Val
mesh_terms: D000136:Acid-Base Equilibrium; D000222:Adaptation, Physiological; D000818:Animals; D001938:Brazil; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002397:Catfishes / Q000502:physiology*; D004777:Environment; D004781:Environmental Exposure; D005618:Fresh Water / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D011188:Potassium / Q000032:analysis / Q000378:metabolism*; D012964:Sodium / Q000032:analysis / Q000378:metabolism*
chemical_list: D012964:Sodium; D011188:Potassium; D002118:Calcium