Hypertonicity stimulates Cl- transport in the intestine of fresh water acclimated eel, Anguilla anguilla

• Published in: Cellular Physiology and Biochemistry
• Main Authors: LIONETTO, Maria Giulia, GIORDANO, Maria Elena, NICOLARDI, Giuseppe, SCHETTINO, Trifone
• Other Authors: Lionetto, Maria Giulia, Giordano, Maria Elena, Nicolardi, Giuseppe, Schettino, Trifone
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2001
• Subjects: cell volume regulation; Na-K-2Cl; intestine; eel; Ringer; Anguilla anguilla
• Online Access: http://hdl.handle.net/11587/300584; https://doi.org/10.1159/000047791

Eel intestinal epithelium when bathed symmetrically with normal Ringer solution develops a net Cl- current (short circuit current, Isc) giving rise to a negative transepithelial potential (Vt) at the basolateral side of the epithelium, lower in fresh-water (FW)-acclimated animals with respect to sea-water (SW). The aim of the present work was to study the cell response to hypertonic stress of FW eel intestinal epithelium in relation to Cl- absorption. The hypertonicity of the external bathing solutions produced first a transient increase of Vt and Isc, then followed (after10-15min) by a gradual and sustained increase which reached the maximum value after 40-60 min. The morphometric analysis of the intestine revealed the shrinkage of the cells after 5 min hypertonicity exposure, and then a regulatory volume increase (RVI) response, which parallels the gradual and sustained increase in the electrophysiological parameters. This last phase is inhibited by drugs known to block Cl- absorption in eel intestine, such as luminal bumetanide (10 M), specific inhibitor of Na+-K+-2Cl- cotransport, or basolateral NPPB (0.5 mM), dichloro-DPC (0.5 mM), inhibitors of basolateral Cl- conductance. Serosal dimethyl-amiloride (100 M), specific inhibitor of the Na+/H+ antiport, was ineffective on the hyperosmotic response. Bicarbonate revealed a crucial role as a modulator of hypertonicity response, since in bicarbonate-free conditions or in the presence of serosal 0.25 mM SITS, blocker of HCO3- transport systems, the Isc response to hypertonicity was lost. In nominally Ca2+-free conditions the Isc response to hypertonicity was abolished. The same results were obtained by bilateral addition of 100 M verapamil or 50 M nifedipine or 1 mM lanthanum, known Ca2+ channel blockers, indicating that extracellular Ca2+ plays a key role for the activation of Cl- current in the response to hypertonic stress. The data show that in the eel intestinal epithelium the hypertonicity of the external medium affects cell volume which in turn might ...