Plasticity of muscle contractile properties following temperature acclimation in the marine fish Myoxocephalus scorpius
Live fibre bundles were isolated from the fast myotomal muscle of short-horned sculpin (Myoxocephalus scorpius L.) and isometric contractile properties and the force&shy;velocity (P&shy;V) relationship determined at 5, 10 and 15 &deg;C. Experiments were carried out on winter- and summer-caught sculpins and on individuals acclimated for 6&shy;8 weeks to either 5 or 15 &deg;C (12 h:12 h light:dark). Maximum tetanic tension (P0) in fibres from 15 &deg;C-acclimated fish increased from 125 kN m-2 at 5 &deg;C to 282 kN m-2 at 15 &deg;C (R10=2.3). For 5 &deg;C-acclimated fish, P0 was 139 kN m-2 at 5 &deg;C, but fell to 78 kN m-2 at 15 &deg;C, consistent with a partial failure of excitation&shy;contraction coupling at high temperatures. Peak force at 15 &deg;C was increased 2.2 times following depolarisation with a high-K+ solution, but was unaffected by the addition of caffeine and/or eserine to the Ringer's solution. The results from winter- and summer-caught fish were similar to those from 5 &deg;C- and 15 &deg;C-acclimated sculpins respectively. In 15 &deg;C-acclimated fish, the power output of muscle fibres calculated from the P&shy;V relationship was 55 W kg-1 at 5 &deg;C and 206 W kg-1 at 15 &deg;C. The P&shy;V relationship at 5 &deg;C was significantly less curved in muscle fibres from 5 &deg;C- than from 15 &deg;C-acclimated fish. After normalizing the curves for P0 and Vmax, it was found that the change in curvature was sufficient to produce a 40 % increase in relative power output at 5 &deg;C in cold-acclimated fish. The maximum contraction speed of muscle fibres at 15 &deg;C was 2.4 times higher in 15 &deg;C- than in 5 &deg;C-acclimated fish. It was concluded that acclimation modifies the contractile properties of fast muscle fibres at both low and high temperatures.
Beddow
T
Johnston
I