Regulation of ion transport by pH and [HCO-3] in isolated gills of the crab Neohelice (Chasmagnathus) granulata.

Posterior isolated gills of Neohelice (Chasmagnathus) granulatus were symmetrically perfused with hemolymph-like saline of varying [HCO3-] and pH. Elevating [HCO3-] in the saline from 2.5 to 12.5 mmol/l (pH 7.75 in both cases) induced a significant increase in the transepithelial potential difference (Vte), a measure of ion transport. The elevation in [HCO3-] also induced a switch from acid secretion (-43.7 ± 22.5 µequivµkg-1µh-1) in controls to base secretion (84.7 ± 14.4 µequivµkg-1µh-1). The HCO3--induced Vte increase was inhibited by basolateral acetazolamide (200 µmol/l), amiloride (1 mmol/l), and ouabain (5 mmol/l) but not by bafilomycin (100 nmol/l). The Vte response to HCO3- did not take place in Cl--free conditions; however, it was unaffected by apical SITS (2 mmol/l) or DIDS (1 mmol/l). A decrease in pH from 7.75 to 7.45 pH units in the perfusate also induced a significant increase in Vte, which was matched by a net increase in acid secretion of 67.8 ± 18.4 µequiv kg-1 h-1. This stimulation was sensitive to basolateral acetazolamide, bafilomycin, DIDS, and Na+-free conditions, but it still took place in Cl--free saline. Therefore, the cellular response to low pH is different from the HCO3--stimulated response. We also report V-H+-ATPase- and Na+-K+-ATPase-like immunoreactivity in gill sections for the first time in this crab. Our results suggest that carbonic anhydrase (CA), basolateral Na+/H+ exchangers and Na+-K+-ATPase and apical anion exchangers participate in the HCO3--stimulated response, while CA, apical V-H+-ATPase and basolateral HCO3--dependent cotransporters mediate the response to low pH. [ABSTRACT FROM AUTHOR]