Metabolic and ionic responses of trout hepatocytes to anisosmotic exposure

GERHARD KRUMSCHNABEL, RONALD GSTIR, CLAUDIA MANZL, CAROLINE PREM, DIEGO PAFUNDO AND PABLO J. SCHWARZBAUM

JOURNAL OF EXPERIMENTAL BIOLOGY

COMPANY OF BIOLOGISTS LTD

Lugar: Londres; Año: 2003 vol. 206 p. 1799 - 1808

0022-0949

Trout hepatocytes exposed to hypo- or hyperosmoticconditions respond by swelling and shrinking,respectively, followed by regulatory volume changes thatalmost, although not completely, restore cell volume.These anisosmotic conditions have a significant impact onmetabolic functions. In hyposmotic medium, oxygenconsumption (V˙ O2) and glucose production rates weresignificantly reduced, whereas lactate accumulation wasnot significantly affected. By contrast, hyperosmoticconditions did not affect V˙ O2 and lactate production butcaused a sustained reduction in glucose production.Volume changes were also accompanied by alterations inintracellular free calcium ([Ca2+]i). At the cell populationlevel, hyposmotic exposure evoked a moderate and slowlydeveloping increase in [Ca2+]i, whereas hyperosmolaritycaused a pronounced and sustained increase, whichpeaked at the time of maximum cell shrinkage but clearlyexceeded a mere concentration effect due to volumereduction. Responses of individual cells were highlyvariable in hyposmotic medium, with only 60% showing aclear increase in [Ca2+]i, while in hyperosmotic conditionsall cells displayed elevated [Ca2+]i levels. A decrease inintracellular pH (pHi) observed in hyposmotic mediumwas insensitive to EIPA, an inhibitor of Na+/H+ exchange,and SITS, an inhibitor of Cl–/HCO3– exchange, but wasprevented in Cl–-free medium. In hyperosmotic medium,pHi increased. This alkalinization did not occur underconditions of blocked Na+/H+ exchange and wassignificantly diminished upon inhibition of Cl–/HCO3–exchange, suggesting an important role of these iontransporters in regulatory volume increase of trouthepatocytes