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How the efficiency of rainbow trout (Oncorhynchus mykiss) ventricular muscle changes with cycle frequency

Claire L. Harwood^*, Iain S. Young and John D. Altringham

School of Biology, University of Leeds, Leeds LS2 9JT, UK
^* Present address: Department of Biology, Leidy Laboratory, University of Pennsylvania, Philadelphia, PA 19104, USA
Present address: Department of Veterinary Preclinical Science, Faculty of Veterinary Science, University of Liverpool, Liverpool L69 7ZJ, UK

View larger version (51K): [in a new window]   Fig. 1. The chamber assembly. The oxygen electrode (oe) was screwed into the chamber body by means of a membrane sleeve (es). Ringer’s solution flowed through the chamber via inlet (chin) and outlet (chout) studs made of Kel-F. A water jacket (wj) surrounded the chamber (ch) and oxygen electrode. Water entered the jacket through a side port (wjin) and exited at the rear of the jacket (wjout). The chloride-coated stimulating electrodes (se) were connected via wires (st) to a Grass S48 stimulator. A temperature probe (tp) was located in the chamber cup and connected to a K-type thermometer (th). The muscle was attached at one end to a servo arm (sa) and at the other end to a force transducer (ft) mounted in a Kel-F stud. A glass-encapsulated stir bar (sb) lay in the cup of the chamber and was used to mix the Ringer’s solution. The glass lid (cl) was sealed using silicon high vacuum grease.

View larger version (21K): [in a new window]   Fig. 2. A sample recording of uncorrected (A) and corrected (B) PO2 (solid line) plotted against time. The dotted lines are linear regressions applied to the decline in PO2 before and during stimulation (B). The cumulative work (open circles) plotted against time for a rainbow trout ventricular preparation is also shown in B. This muscle was subjected to 300 work loops (5 min) at 1.0 Hz. Starting length (L0) was 95 % Lmax, where Lmax is the length for maximum isometric force production, strain was ±8 % L0 (16 % peak-to-peak) and phase of stimulation (circles on work loops) was 30°. Representative work loops from cycles 10, 50, 100, 200 and 300 are also illustrated (C). The loops are counterclockwise, with their area representing net work. Arrows indicate the direction of travel and the stimulus timing is indicated by a filled circle.

View larger version (14K): [in a new window]   Fig. 3. The effects of cycle frequency on net oxygen consumption (O2) and its energetic equivalent (O2). Values are means ± S.E.M., N=5–8.

View larger version (17K): [in a new window]   Fig. 4. The effects of cycle frequency on net work (circles) and the rate of energy utilisation, O2, per cycle (squares). Values are means ± S.E.M., N=5–8.

View larger version (23K): [in a new window]   Fig. 5. The effects of cycle frequency on total efficiency (total power output divided by the sum of resting and active rates of energy consumption) (diamonds), net efficiency (squares) and total power output, Ep (circles). Values are means ± S.E.M., N=5–8. and * indicate statistically significant differences (P<0.05, ANOVA) from 0.6 Hz and 1.0 Hz, respectively.