Thermal Dependence of Isometric Contractile Properties of Lizard Muscle

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  1. The thermal dependence of the isometric contractile properties of the iliofibularis and gastrocnemius muscles were studied at 5°C intervals from 10–50°C in lizards with different preferred body temperatures (PBT): Dipsosaurus dorsalis (PBT: 40–42°C); Cnemidophorus murinus (40°C); Sceloporus occidentalis (35°C); and Gerrhonotus multicarinatus (25–30°C).

  2. Isometric twitch and tetanic tensions were constant over a broad temperature range (as much as 25°C) in all species. Tetanic tension declined by 50% at 45–47.5°C inDipsosaurus, 42.5°C inCnemidophorus, and 40°C inSceloporus andGerrhonotus.

  3. Twitch contraction time (CT-the time to the peak twitch tension) increased with decreasing temperature from 10 ms to 300 ms. At any given temperature, the muscles ofSceloporusandGerrhonotus had faster CTs than those of the other species. The CTs were minimal at the maximal test temperature.

  4. The maximal rate of tension development with tetanic stimulation (dPo/dt) was strongly temperature dependent and was maximal at 40–45°C in Dipsosaurus, 40–42.5°C in Cnemidophorus, and 35°C in Sceloporus and Gerrhonotus.

  5. The time properties of these muscles are highly temperature dependent and contractile tensions are broadly temperature independent. Except in Gerrhonotus muscles, the combination of twitch speed and tension generating capability is maximal at PBT, although neither parameter alone is maximized at PBT.