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

At a muscle length L0 (just taut), isometric tension and ATPase activity were measured at constant levels of various Ca2+ activations in muscle fibres (2-3 mm long and 34-66 microns in diameter) isolated from temporal, masseter and digastric (anterior belly) muscles. The isometric tension increased in a sigmoid fashion with increasing Ca2+ 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 preparations of each muscle averaged 44.4 +/- 6.6 g/mm2 in the temporalis, 31.9 +/- 4.0 g/mm2 in the masseter, and 23.9 +/- 5.5 g/mm2 in the digastric. The ATPase activity also increased sigmoidally with increasing Ca2+ 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 mumol/mg protein per min in the temporalis, 0.29 +/- 0.06 mumol/mg protein per min in the masseter, and 0.18 +/- 0.04 mumol/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.