Abstract
Single fibres were isolated from the ‘red’ and ‘white’ portions of the iliofibularis muscle from the desert iguana (Dipsosaurus dorsalis). Muscle fibres were chemically skinned with the non-ionic detergent Brij. 58.
Maximal Ca2+-activated tensions at 40°C were 32·3 ± 1·5 N cm-2 for red and 33·0 ± 24 N cm-2 for white muscle fibres (mean ± S.E. mean). Unloaded contraction velocities (Vmax) were determined by the ‘slack-test’ method. Average values for Vmax at 40°C were 7·1 ±0·4 and 164 ± 14 muscle length s-1 (Lo s-1) for red and white fibres respectively. The red portion of the iliofibularis contained fibres with Vmax values between 14 and 12·9 Los-1. Around 18% of the red fibre population had maximum contraction velocities less than 4·0Los-1. These slower fibres were principally located in the region closest to the femur in situ. They probably correspond to the multiply-innervated ‘tonic type’ fibres that can be identified histochemically.
Q10 values for Vmax over the range 5·15 °C were higher for red (4·2) than white (2·3) muscle fibres. Above 25·30 °C Q10 values for Vmax were in the range 1·3−1·9 for both fibre types. Maximum Ca2+-activated tensions were largely independent of temperature between 20 and 45 °C. Dipsosaurus is maximally active in the field at 35·42 °C, which corresponds to a 2one of relative thermal independence of muscle contractile properties and locomotory performance.
