Interessanter Artikel - Calcium und Fische - L-Welse.com Forum

Walter · 23.01.2006, 21:57

Frei nach Stefan, war´s eine der Arbeiten:

Gonzalez, R. J. und Preest, M. R. (1999). Ionoregulatory specializations for exceptional tolerance of ion-poor, acidic waters in the neon tetra (Paracheirodon innesi). Physiological and Biochemical Zoology 72 (2): 156-163.

ABSTRACT

To better understand how fish are able to inhabit dilute waters of low pH, we examined ionoregulation in exceptionally acid-tolerant neon tetras (Paracheirodon innesi), which are native to the ion-poor, acidic Rio Negro, Amazon. Overall ion balance was unaffected by 2-wk exposure to pH 4.0 and 3.5. Measurements of unidirectional Na+ fluxes during exposure to pH 3.5 showed that tetras experienced only a mild, ionic disturbance of short duration (

24 h) as a result of a stimulation of Na+ efflux. At pH 3.25, Na+ efflux was almost fourfold greater (all fish died within 6

8 h). At both pHs, active Na+ uptake was not inhibited, and in fact, at pH 3.5, uptake was stimulated. Kinetic analysis of Na+ uptake at pH 6.5 and 3.5 produced virtually identical low Km values and high maximum-transport values. These results confirmed the pH insensitivity of the uptake mechanism and revealed a mechanism well designed to operate in the dilute, acidic waters of the Rio Negro. Na+ influx was only mildly sensitive to amiloride (a Na+ channel blocker), which, along with the pH insensitivity, suggests that Na+ uptake may occur by a novel mechanism. Na+ efflux was reduced by addition of Ca2+ to the test water at pH 6.5, but the effect disappeared at pH 3.5. Exposure to LaCl3 (a strong Ca2+ displacer) also stimulated Na+ efflux. These results suggest that Ca2+ plays a role in determining branchial ion permeability at high pH but that, at low pH, where Na+ efflux is stimulated, alternate, Ca2+-independent mechanisms are employed to control Na+ efflux.

Gonzalez, R. J., Wood, C. M., Wilson, R. W., Patrick, M. L., Bergman, H. L., Narahara, A. und Val, A. L. (1998). Effects of water pH and calcium concentration on ion balance in fish of the Rio Negro, Amazon. Physiological Zoology 71 (1): 15-22.

23.01.2006, 21:57	#5
Walter Herr Prof. Obermoserer Registriert seit: 02.01.2003 Ort: Wien Beiträge: 4.130	Frei nach Stefan, war´s eine der Arbeiten: Gonzalez, R. J. und Preest, M. R. (1999). Ionoregulatory specializations for exceptional tolerance of ion-poor, acidic waters in the neon tetra (Paracheirodon innesi). Physiological and Biochemical Zoology 72 (2): 156-163. ABSTRACT To better understand how fish are able to inhabit dilute waters of low pH, we examined ionoregulation in exceptionally acid-tolerant neon tetras (Paracheirodon innesi), which are native to the ion-poor, acidic Rio Negro, Amazon. Overall ion balance was unaffected by 2-wk exposure to pH 4.0 and 3.5. Measurements of unidirectional Na+ fluxes during exposure to pH 3.5 showed that tetras experienced only a mild, ionic disturbance of short duration (24 h) as a result of a stimulation of Na+ efflux. At pH 3.25, Na+ efflux was almost fourfold greater (all fish died within 68 h). At both pHs, active Na+ uptake was not inhibited, and in fact, at pH 3.5, uptake was stimulated. Kinetic analysis of Na+ uptake at pH 6.5 and 3.5 produced virtually identical low Km values and high maximum-transport values. These results confirmed the pH insensitivity of the uptake mechanism and revealed a mechanism well designed to operate in the dilute, acidic waters of the Rio Negro. Na+ influx was only mildly sensitive to amiloride (a Na+ channel blocker), which, along with the pH insensitivity, suggests that Na+ uptake may occur by a novel mechanism. Na+ efflux was reduced by addition of Ca2+ to the test water at pH 6.5, but the effect disappeared at pH 3.5. Exposure to LaCl3 (a strong Ca2+ displacer) also stimulated Na+ efflux. These results suggest that Ca2+ plays a role in determining branchial ion permeability at high pH but that, at low pH, where Na+ efflux is stimulated, alternate, Ca2+-independent mechanisms are employed to control Na+ efflux. Gonzalez, R. J., Wood, C. M., Wilson, R. W., Patrick, M. L., Bergman, H. L., Narahara, A. und Val, A. L. (1998). Effects of water pH and calcium concentration on ion balance in fish of the Rio Negro, Amazon. Physiological Zoology 71 (1): 15-22. __________________ Grüße, Walter