Low pH and high [HCO3−] stimulate ion transport across isolated gills of the crab Chasmagnathus granulatus via different cellular mechanisms

PARKS, S.K., TRESGUERRES, M., SABATINI, S.E., LUQUET, C.M., AND GOSS, G.G.

Salvador, Bahia, Brasil

Congreso; 7th International Congress of Comparative Physiology and Biochemistry; 2007

The Society for Comparative Physiology and Biochemistry

Posterior isolated gills of Chasmagnathus granulatus were symmetrically perfused with haemolymph-like saline of varying  pH and [HCO3−] while the transepithelial potential difference (Vte) was recorded as an indication of net ion transport. A decrease in pH from 7.75 to 7.45 in the perfusate stimulated the outside-positive Vte by 70%. This stimulation was sensitive to basolaterally applied acetazolamide (200 μmol l−1), bafilomycin (100 nmol l−1) and DIDS (2 mmol l−1), which indicates that carbonic anhydrase (CA), V–H+-ATPase and Na+/HCO3− cotransporters are involved in the mechanism of pH recovery. The low-pH stimulation of Vte also took place in Cl−-free conditions, indicative of a Cl−-independent mechanism. An increase of [HCO3−] from 2.5 to 12.5 mmol l−1 also stimulated Vte and was accompanied by an elevation of the pH in the bath surrounding the gill suggesting net base secretion. This HCO3- −stimulated Vte was completely inhibited by basolateral application of amiloride (1 mmol l−1) and acetazolamide but not by bafilomycin. The Vte response to HCO3− did not take place in Cl−-free conditions. These results indicate that an elevation in HCO3− stimulates ion transepithelial transport via a mechanism that includes apical anion exchangers, CA and basolateral Na+/H+ exchangers. Our results culminate in a model for the H+ and HCO3− secreting processes at the gill of C. granulatus