ACID-BASE REGULATION IN TADPOLES OF RANA-CATESBEIANA EXPOSED TO ENVIRONMENTAL HYPERCAPNIA

Tadpoles of Rana catesbeiana were exposed to different levels of envir onmental hypercapnia. The acid-base regulatory response differed from that in adult amphibians in showing a high degree of pH compensation i n the extracellular fluid (65-85%) and complete compensation in the in tracellular fluid (tail muscle and liver) within 24h. Hypercapnia indu ced a massive transfer of HCO3- equivalents and Ca2+ from the tadpoles to the environment, which lasted some 4-6h. Bicarbonate accumulated i n the body fluids came mainly from internal buffer sources (probably C aCO3 in lime sacs and/or skin deposits). It is suggested that the larg e bicarbonate efflux from the animal is a consequence of the dissoluti on of CaCO3 stores and the delayed adjustment of bicarbonate-retaining mechanisms. Re-exposure of tadpoles to hypercapnia after 1-3 weeks of normocapnic recovery only affected transepithelial fluxes of acid-bas e equivalents marginally, suggesting that mobilisable CaCO3 stores wer e depleted during the first exposure to hypercapnia and that they were not refilled. The CaCO3 stores may normally be mobilised during the s lowly developing internal hypercapnia that occurs during metamorphosis .