EFFECTS OF TEMPERATURE-ACCLIMATION ON MUSCLE-RELAXATION IN THE CARP - A MECHANICAL, BIOCHEMICAL, AND ULTRASTRUCTURAL-STUDY

Common carp (Cyprinus carpio L.) were acclimated to either 5–8°C or 20–25°C for a minimum of 1 month, and the twitch contraction kinetics of a myotomal nerve‐muscle preparation were investigated. A significant compensation for the acute effects of temperature was achieved in twitch kinetics by acclimation to 8°C. An acute drop in temperature from 20 to 8°C in preparations from warm‐acclimated fish led to approximately two‐ to three‐fold increases in the half‐times for activation and relaxation. At 8°C, values were 50% faster in 8°C‐ than in 20°C‐acclimated fish, indicating a partial capacity adaptation in rates of both twitch activation and relaxation. The mechanisms underlying temperature compensation of twitch contraction kinetics were investigated. A quantitative ultrastructural study was performed on the sarcoplasmic reticulum (S.R.) of fast and slow myotomal muscles. No differences were found in the surface and volume densities of the S.R. in fast‐twitch fibres between cold‐ and warm‐acclimated fish. The surface densities of terminal cisternae and S.R. were higher in slow‐twitch fibres from the warm‐acclimated fish. Parvalbumin concentration in fast fibres was found to be independent of acclimation temperature (0.61–0.68 mmol/kg wet weight). Although the relative proportions of parvalbumin isoforms (I–IV) showed considerable individual variation this was not correlated with environmental temperature. The Ca2+‐ATPase activity of S.R.‐enriched microsomes prepared from fast myotomal muscle was 60% higher at 8°C in cold‐ than warm‐acclimated carp. This suggests that changes in the kinetics and/or density of Ca2+ pumps contribute to the observed capacity adaptation in relaxation rate with temperature acclimation. Other possible mechanisms underlying the plasticity of twitch contraction kinetics in carp are briefly discussed. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company