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Regulation of cardiac contractility in a cold stenothermal fish, the burbot Lota lota L.

Virpi Tiitu and Matti Vornanen^*

University of Joensuu, Department of Biology, PO Box 111, 80101 Joensuu, Finland

View larger version (16K): [in a new window]   Fig. 1. Temperature-dependence of contractility in spontaneously beating perfused burbot hearts with acute temperature changes from 1±0.5 °C to 18±0.5 °C. (A) Heart rate, (B) maximum developed force Fmax, (C) time course of contraction, (D) pumping capacity of the heart (Fmaxxheart rate). Values are means ± S.E.M. from eight hearts.

View larger version (15K): [in a new window]   Fig. 2. Effect of ryanodine on the contractility (maximum developed force Fmax) of burbot atrial and ventricular muscle at 1 ° and 7 °C, normalized against control value (at 1 or 7 °C). Values are means ± S.E.M. of 5 preparations for both atrial and ventricular tissue. *Statistically significant difference (P<0.05) between values of control at both 1 °C and 7 °C and after ryanodine treatment (+Ry); , between atrial and ventricular muscle.

View larger version (23K): [in a new window]   Fig. 3. Force and relaxation restitution of the burbot atrial and ventricular muscle in the absence (open symbols) and presence (filled symbols) of 10 µmoll-1 ryanodine. FES (A) and dF/dtmin (B) are plotted as a function of the extrasystolic interval (t) and the plots were fitted by single exponential equations. Values are means ± S.E.M. of 5 preparations. The experiments were conducted at 1±0.5°C. See Materials and methods for details.

View larger version (19K): [in a new window]   Fig. 4. Transition from rest-potentiation into rest-decay after ryanodine (10 µmoll-1) treatment in atrial and ventricular muscule of the burbot heart at 1±0.5°C. (A) Representative recordings of rest-potentiation (control) and rest-decay (ryanodine) in atrial (left) and ventricular (right) muscle. Note the prolonged twitch duration after rest in the ventricular preparation. (B) The correlation between the maximum force of contraction Fmax and the duration of contraction TDC in atrial and ventricular preparations in the absence (open symbols) and presence (filled symbols) of ryanodine. The direction of the arrows indicates a positive or negative correlation for atrial (solid lines) and ventricular (broken lines) force and duration of contraction. (C) Mean results (± S.E.M.; N=5) of Fmax for the first twitch after a 10, 30 or 60 s rest period in the absence (open bars) and presence (filled bars) of ryanodine. **Value significantly different from control (P<0.05).

View larger version (13K): [in a new window]   Fig. 5. Ca2+/Mg2+-ATPase activity of the purified atrial and ventricular myofibrils of the burbot heart. The experiments were conducted at four different temperatures (1, 5, 10 and 15 °C). Dissimilar letters indicate statistically significant differences between different temperatures. Values are means ± S.E.M. of 5-7 preparations.

View larger version (14K): [in a new window]   Fig. 6. Species-specific differences in heart rate (A), duration of contraction TDC (B) and activity of myofibrillar ATPase of atrial muscle (C) between cold-acclimated (4 °C) rainbow trout, cold-acclimated (4 °C) crucian carp and cold-adapted (1 °C) burbot. Dissimilar letters indicate statistically significant differences (P<0.05) between species. Values are means ± S.E.M. of 5-7 preparations as indicated. The data for myofibrillar ATPase activity (C) of rainbow trout and crucian carp are from Aho and Vornanen (1999) and Tiitu and Vornanen (2001), respectively.