QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online August 9, 2007
Journal of Experimental Biology 210, 2843-2850 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006379

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Trinh, M. Articles by Syme, D. A. Search for Related Content PubMed PubMed Citation Articles by Trinh, M. Articles by Syme, D. A.

Effects of stretch on work and efficiency of frog (Rana pipiens) muscle

Michelle Trinh and Douglas A. Syme^*

Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

View larger version (5K): [in this window] [in a new window]   Fig. 1. Experimental apparatus used to measure oxygen consumption and work. Muscle (mu) was mounted in a cylindrical glass chamber (bound by broken lines) surrounded by a temperature controlled water jacket (wj). One end of the muscle was attached to a rigid, stainless-steel arm (ra) secured to the stainless-steel chamber lid (cl). The other end was attached to a stainless-steel pin (pn) that passes through a narrow aperture in the lid and was connected to the arm of an ergometer (er). A glass-encapsulated magnetic stir bar (sb) was used to mix the saline in the chamber. An oxygen probe (op) enters the chamber through a sealed side port. A temperature probe (tp) was placed adjacent to the chamber. To flush the chamber, saline entered through a port in the bottom (arrow) and exited through the hole in the chamber lid; diameter of holes in chamber lid and bottom are exaggerated for illustration purposes. Chamber lid and bottom formed a tight seal with the walls of the chamber using rubber O-rings. The rigid arm and pin connected to the ends of the muscle were attached to fine magnet wires outside the chamber (not shown) and used to stimulate the muscle. The rigid arm was insulated along its length with polyethylene tubing to minimize stray current in the chamber.

View larger version (10K): [in this window] [in a new window]   Fig. 2. Records of the partial pressure (PO2) of oxygen in the chamber during the course of one series of measurements in two different muscles (top and bottom traces). The initial decline in PO2 as a result of resting metabolism in the muscle is followed by a more rapid decline when the muscle is stimulated to do work, which is then followed by a return to the resting rate when the muscle ceases working. The vertical separation between regressions fit to the initial and final resting rates, evaluated about half way between the onset and termination of work (line with arrowheads), is used to measure the change in PO2 that occurred while the muscle was working.

View larger version (5K): [in this window] [in a new window]   Fig. 3. Examples of the four protocols used to measure work done and cost of the different contractions, as described in Materials and methods. (A) Muscle length (upper traces) and force (lower traces) during shortening contractions preceded by either an isometric phase (protocol i) or stretch (protocol ii). Triangles indicate onset (up) and termination (down) of stimulation. (B) Muscle length (upper) and force (lower) during either a purely isometric contraction (protocol iii) or an isometric contraction preceded by a stretch (protocol iv). Lo is muscle length giving maximal, isometric twitch force. Scale bars indicate muscle length (mm), force (mN) and time (ms).

View larger version (5K): [in this window] [in a new window]   Fig. 4. Cumulative work done during 10 contractions in the protocols described in the Materials and methods and in Fig. 3. `I', shortening contractions preceded by an isometric phase; `S', shortening contractions preceded by a stretch; `shorten', the work done during the shortening portion of the contraction; `net', the net work done during the entire contraction (note: for contractions preceded by an isometric phase, net work equals shortening work); `stretch', the work required to stretch the muscle. Work is expressed relative to muscle mass. Values are means ± s.e.m. P values are comparisons with I-shorten using work values uncorrected for muscle mass.

View larger version (5K): [in this window] [in a new window]   Fig. 5. Cumulative metabolic cost over 10 contractions, derived from oxygen consumption as described in Materials and methods. `I', shortening contractions preceded by an isometric phase; `S', shortening contractions preceded by a stretch; `Isometric', cost of a 100 ms isometric contraction; `Stretch', cost of a 25 ms stretch followed by 75 ms isometric contraction. Cost is expressed relative to muscle mass. Values are means ± s.e.m. P values compare the measurements that they straddle using values uncorrected for muscle mass.

View larger version (5K): [in this window] [in a new window]   Fig. 6. Efficiency of muscle work measured over 10 contractions, derived from work and oxygen consumption as described in Materials and methods. `I', shortening contractions preceded by an isometric phase; `S', shortening contractions preceded by a stretch; `net', calculations using the net work done during the entire contraction; `shorten', calculations using the work done during only the shortening portion of the contraction, but still the energy used during the entire contraction. Values are means ± s.e.m. P values compare the two measurements that they straddle.