ATPase activity and tension development in mechanically-skinned feline jaw muscle

Abstract

At a muscle length L 0 (just taut), isometric tension and ATPase activity were measured at constant levels of various Ca 2+ activations in muscle fibres (2–3 mm long and 34–66 μm in diameter) isolated from temporal, masseter and digastric (anterior belly) muscles. The isometric tension increased in a sigmoid fashion with increasing Ca 2+ concentration from about pCa 6.60 to pCa 5.00 in the temporalis and from about pCa 6.37 to pCa 5.00 in both the masseter and digastric. The maximum isometric tension from four perparations of each muscle averaged 44.4 ± 6.6 g/mm 2 in the temporalis, 31.9 ± 4.0 g/mm 2 in the masseter, and 23.9 ± 5.5 g/mm 2 in the digastric. The ATPase activity also increased sigmoidally with increasing Ca 2+ concentration from slightly below pCa 7.0 to pCa 5.0 in the temporalis, and from slightly above pCa 6.0 to pCa 5.0 in both the masseter and digastric. The maximum ATPase activity obtained from four preparations of each muscle averaged 0.35 ± 0.06 μmol/mg protein per min in the temporalis, 0.29 ± 0.06 μmol/mg protein per min in the masseter, and 0.18 ± 0.04 μmol/mg protein per min in the digastric. The tension cost (ATPase activity/tension) estimated from these results was lower in the digastric than in the temporalis or masseter, indicating more economical ATP consumption in the digastric.