Regulation of Ion Transport by Ph And [Hco3-] In Isolated Gills Of The Crab Neohelice (Chasmagnathus) granulata

TRESGUERRES, MARTIN; PARKS, SCOTT; SABATINI, SEBASTIÁN; GOSS, GREG; LUQUET, CARLOS

THE AMERICAN JOURNAL OF PHYSIOLOGY.

AMER PHYSIOLOGICAL SOC

Año: 2008 p. 1033 - 1043

0002-9513

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 equiv kg h) in controls to base secretion (84.7+-14.4 equiv kg h). The HCO3 -induced Vte increase was inhibited by basolateral acetazolamide (200 _mol/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 _equiv 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.