title: Force generation upon hydrostatic pressure release in tetanized intact frog muscle fibres.
abstract: Single intact muscle fibres isolated from the tibialis anterior muscle of the frog were exposed to hydrostatic pressures of 1-10 MPa, at 2-4 degrees C and sarcomere length of 2.1-2.2 microm. The pressure was rapidly released (ca. 1 ms) to atmospheric level (0.1 MPa) during the plateau of a tetanic contraction (Po) and the resultant tension (= force) transient examined. The pressure release induced tension transient consisted of an initial tension drop coincident with pressure release (ca. 4% Po per MPa, Phase 1), followed by a rapid recovery (Phase 2a) and a slower rise of tension (Phase 2b). Phase 1 was partly due to a length release at fibre ends (ca. 0.1 nm per half-sarcomere per MPa) induced by pressure-release effects on the steel chamber and fibre attachments, and partly due to 'expansion' upon pressure release within muscle fibre (ca. 0.2 nm per half-sarcomere per MPa), probably in the myofilaments and cross-bridges. The rate of tension recovery during phase 2a (ca. 600/s) was comparable to that of the quick tension recovery (T1-T2 transition) reported from moderately fast small length releases; the time course of Phase 2b (rate ca. 40/s) was similar to the late phase of tension rise in a tetanus, and hence compared with Phase 4 (T4) of a length release tension transient. Results are compared with the previously reported findings from analogous experiments on Ca2+ -activated skinned (rabbit) muscle fibres.
authors.affiliation: Department of Physiology, School of Medical Sciences, University of Bristol, UK.
authors.forename: F
authors.initials: F
authors.lastname: Vawda
authors.forename: M A
authors.initials: MA
authors.lastname: Geeves
authors.forename: K W
authors.initials: KW
authors.lastname: Ranatunga
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D006874:Hydrostatic Pressure; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D011817:Rabbits; D011896:Rana temporaria; D012518:Sarcomeres / Q000502:physiology