Contractile activation and force generation in skinned rabbit muscle fibres: effects of hydrostatic pressure.
1. Effects of hydrostatic pressure (range 0.1-10 MPa) on the isometric tension of skinned (rabbit psoas) muscle fibres were examined at 12 degrees C and at different levels of Ca2+ activation (pCa range 4-7); the effects on both the steady tension and the tension transients induced by rapid pressure release (< 1 ms) are described. 2. The steady tension was depressed by increased pressure (approximately 1% MPa-1) at a high level of Ca2+ activation (pCa approximately 4) whereas it was potentiated at lower Ca2+ levels (pCa > 6); the effects were reversible. 3. At maximal Ca2+ activation, the tension recovery following pressure release (10 MPa to atmospheric) consisted of a fast (approximately 30 s-1) and a slow (2-3 s-1) phase; the rate and the normalized amplitude (normalized to the steady tension at atmospheric pressure for a particular pCa) of the fast phase were invariant with changes in Ca2+ level. 4. The effects of changing Ca2+ level on the slow phase were complex; its positive amplitude at high Ca2+ levels changed to negative and the rate decreased to approximately 1 s-1 at low Ca2+ levels (pCa > 6.0). 5. Results are discussed in relation to previous studies on the effect of pressure on intact muscle fibres and the actin-myosin interaction. This work supports calcium regulation of cross-bridge recruitment rather than calcium regulation of the rate of a specific step in the cross-bridge cycle.
Fortune
N S
NS
Department of Physiology, School of Medicine, University of Bristol.
Geeves
M A
MA
Ranatunga
K W
KW
D000818:Animals; D001274:Atmospheric Pressure; D002118:Calcium / Q000502:physiology; D006874:Hydrostatic Pressure; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D009132:Muscles / Q000166:cytology / Q000294:innervation / Q000502:physiology*; D016658:Psoas Muscles / Q000166:cytology / Q000502:physiology; D011817:Rabbits; D011999:Recruitment, Neurophysiological / Q000502:physiology
D002118:Calcium