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Otolith growth in trout Oncorhynchus mykiss: supply of Ca²⁺ and Sr²⁺ to the saccular endolymph

P. Payan^1,*, G. Borelli¹, F. Priouzeau¹, H. De Pontual², G. Buf³ and N. Mayer-Gostan¹

¹ Laboratoire R.O.S.E. (Réponses des Organismes aux Stress Environnementaux), UMR 1112, INRA-UNSA, Université de Nice-Sophia Antipolis, Faculté des Sciences, Parc Valrose, 06108 Nice Cedex 2, France
² IFREMER, DRV, RH, Laboratoire de Sclérochronologie des Animaux Aquatiques, BP 70, 29280 Plouzane, France
³ Observatoire Océanologique, Laboratoire Arago, Université de Pierre et Marie Curie, CNRS 639, BP 44, 66651, Banyuls sur Mer Cedex, France

View larger version (23K): [in a new window]   Fig. 1. Schematic drawing of the retroperfusion technique used to study Ca2+ fluxes across the saccular epithelium of trout. Solid arrows, in vivo blood circulation; open arrows, Ringer perfusion.

View larger version (17K): [in a new window]   Fig. 2. Effects of plasma hypercalcemia on calcium levels in the endolymph of trout. (A) Time course of calcium concentrations in plasma (solid circles), proximal (open circles) and distal (solid squares) endolymphs after intraperitoneal injection (at time 0 min) of 100 µl 0.5 mol l-1 CaCl2. (B) Relationships between calcium concentrations in proximal (solid symbols) and distal (open symbols) and plasma endolymph. Curve-fitting was done using Igor Pro 4.01 (Wavemetrics Inc).

View larger version (15K): [in a new window]   Fig. 3. Ca2+ influx measured by 45Ca2+ appearance in proximal (solid circles) and distal (open circles) endolymphs during perfusion of the inner ear of trout with radioactive Ringer solution under equilibrium conditions.

View larger version (19K): [in a new window]   Fig. 4. Calcium levels in endolymph in the presence of chemical gradients of calcium across the saccular epithelium of perfused inner ear of trout. (A) Proximal endolymph, (B) distal endolymph. The value at time 0 min (hatched colums) is the calcium content of endolymph before starting the perfusion. The inner ear was then perfused with a Ringer solution containing different concentrations of calcium (0.19 mmol l-1, white bars; 3.22 mmol l-1, grey bars; 4.40 mmol l-1, black bars). Endolymph was sampled in the left saccule at 35 min and in the right saccule at 70 min. N values are given in parentheses. NS, not significant; *P<0.01; **P<0.001 in comparison with control values.

View larger version (18K): [in a new window]   Fig. 5. Calcium levels in endolymph in the presence of chemical gradients of calcium across the saccular epithelium of perfused inner ear of trout. (A) Proximal endolymph, (B) distal endolymph. Values at time 0 min (hatched columns) are the calcium content of endolymph before starting the perfusion. The inner ear was then perfused with a Ringer solution containing 3.23 mmol l-1 calcium and 35 min later endolymphs were sampled in the left saccule. The perfusion was then either continued with the same [Ca]-Ringer, or with different concentrations of Ca-Ringer (0.19 mmol l-1, white bars; 3.22 mmol l-1, grey bars; 4.40 mmol l-1, black bars) and at t=70 min the endolymph was sampled in the right saccule. N values are given in parentheses. NS, not significant; *P<0.01; **P<0.001, for comparison between t=35 min and t=70 min.

View larger version (11K): [in a new window]   Fig. 6. Relationship between concentration of [Ca2+] and [protein] in endolymph of trout.

View larger version (18K): [in a new window]   Fig. 7. Relationships between Ca2+ entry into the endolymph and the chemical gradient of calcium across the saccular epithelium of trout. Ca2+ entry (mmol l-1 35 min-1) corresponds to the difference in endolymph calcium levels between t=0 and t=35 min, by which time equilibrium was reached (see Results, Fig. 4). Calcium gradient (mmol l-1) corresponds to the difference between calcium levels in the endolymph and the Ringer solution at the beginning of the perfusion. Regression lines are shown together with their equations and significances, which have been calculated with paired data. N values are given in parentheses.

View larger version (17K): [in a new window]   Fig. 8. Relationships between Sr2+ entry into the endolymph and the chemical gradient of strontium across the saccular epithelium of trout. Other details as in Fig. 7.

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