Temperature dependence of the crossbridge cycle during unloaded shortening and maximum isometric tetanus in frog skeletal muscle

Abstract

The primary objective of this study was to determine if the rate limiting step in the crossbridge cycle was the same during maximum rate of shortening and during maintenance of maximum tension in an isometric contraction. To this end the temperature dependence, Q10, of the crossbridge cycle was estimated during unloaded shortening and maximum isometric tetanus. Isolated semitendinosus muscles from the frog were studied at 0 and 10 degrees C. Crossbridge cycling during unloaded shortening was determined from the velocity of unloaded shortening estimated by the slack step technique. Crossbridge cycling during maintained isometric tetanus was determined from the steady rate of energy liberation during the tetanus after allowance for energy liberation due to Ca2+ cycling. The Q10 of the velocity of unloaded shortening was 2.5 and that of the steady rate of energy liberation was 4.6. After correction for the temperature dependence of energy liberation associated with Ca2+ cycling (5.7), the estimated Q10 of the steady rate of energy liberation became 3.9. These estimates of the Q10 of the crossbridge cycle are significantly different. These results support the conclusion that the rate limiting steps during unloaded shortening and maximum isometric force maintenance occur at different steps in the crossbridge cycle. Further the high Q10 of the energy liberation due to Ca2+ cycling may relate to the high concentration of parvalbumin in frog muscle. A second objective of this study was to document in the same muscle the variation of Q10s of mechanical and energetic properties of contraction. Over this temperature range the Q10s ranged from 1.1 to 5.7.

Myofibrillar ATPase activity in skinned human skeletal muscle fibres: fibre type and temperature dependence.

“…Boska, 1991;Blei et al 1993a,b;Turner et al 1993 (Godt & Lindley, 1982;Burchfield & Rall, 1986), intact muscle fibres from mouse (Liinnergren & Westerblad, 1987) and human muscle (Ranatunga, Sharpe & Turnbull, 1987). These studies indicate that the temperature dependence of force production decreases when the temperature increases.…”

“…Burchfield & Rall, 1986) and on single fibres (Curtin, Howarth, Rall, Wilson & Woledge, 1986) (Zhao & Kawai, 1994), while in human fibres (this study) a Qlo of 2-6 was found. …”

Differential effects of length on maximum force production and myofibrillar ATPase activity in rat skinned cardiac muscle.

“…This value is somewhat greater than in previous studies with other cardiac muscle preparations. For example, in pig skinned myocardium the turnover was 0-5 s-' at 24°C (Kuhn, Bletz & Riiegg, 1990) and in guinea-pig skinned trabeculae it was 0 4 s' at 12°C (Barsotti & Ferenezi, 1988), which is equivalent to 1P4 s' at 21°C (assuming a Q10 of 4; Burchfield & Rall, 1986). Our higher value for ATP turnover may be because we measured this at optimal SL and in a species (rat) of an age (1P5 months) where the myosin isozyme is almost exclusively the fast V1 form (Horowits & Winegrad, 1987).…”

Malignant hyperthermia: Effects of sarcoplasmic reticulum Ca2+ pump inhibition

“…At 26°C the prolonged twitch can be attributed to an elongation of the Ca 2+ transient 1 and/or the slowing of crossbridge cycling. 2 Since there are no known differences in the contractile proteins of MHS muscles 18 which could account for the greater temperature sensitivity, we attribute this difference to an altered Ca 2+ homeostasis in MHS muscles. This conclusion was supported by our findings with CPA, which should have identical inhibitory effects on the SR pump of both muscle types, since the SR Ca…”

“…The SR Ca 2+ pump can be slowed by cooling the muscle; however, this also alters the cross-bridge kinetics, 2 making it difficult to distinguish between possible effects on Ca 2+ uptake and on the contractile apparatus. Cyclopiazonic acid (CPA) is a potent and specific inhibitor of the SR Ca 2+ pump, 14 making it a useful probe of the role of the SR Ca 2+ adenosine triphosphatase (ATPase) in muscle relaxation.…”