Regulation of ion transport by pH and [HCO3-] in isolated gills of the crab Neohelice (Chasmagnathus) granulata.

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

AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY, INTEGRATIVE AND COMPARATIVE PHYSIOLOGY

The American Physiological Society

Lugar: Bethesda MD; Año: 2008 vol. 294 p. 1033 - 1043

0363-6119

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 µequiv  kg_1  h_1) in controls to base secretion (84.7 ± 14.4 µequiv kg_1 h_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.