. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CD U 200 175 150 125 .100 75 50 25 0. Length (ML) Figure 1. (A) Tetanic force ink v\ alter addition of progressively higher concentrations of CPA on a red muscle bundle. Force traces are normalized to the maximum tone of each tetanus. Each tetanus had a stimulus duration of 125 ins (shown in bottom left of figure). T,QO_IO relaxation time increased from 133 ms prior to CPA to 163, 218. and 395 ms after , and pM CPA. respectively. (B) Effect of the different relaxation times shown in
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CD U 200 175 150 125 .100 75 50 25 0. Length (ML) Figure 1. (A) Tetanic force ink v\ alter addition of progressively higher concentrations of CPA on a red muscle bundle. Force traces are normalized to the maximum tone of each tetanus. Each tetanus had a stimulus duration of 125 ins (shown in bottom left of figure). T,QO_IO relaxation time increased from 133 ms prior to CPA to 163, 218. and 395 ms after , and pM CPA. respectively. (B) Effect of the different relaxation times shown in (A) on power production. Work loops are at : muscle oscillation frequency, strain. -48° phase, and 7 5-ms stimulus duration. Power valuer decreased from 4f>.N \\'kg'1 prior to CPA to \Vkg~'. I? 4 \Vkg~' and. »'kg'1 after 10. , and iM CPA. Note that at 5 fiM the work loop is generated in a clockwise direction, indicating that the muscle is having net work done on it (negative work). All other work loops are counterclockwise (positive work) Length changes are given in muscle lengths (ML). ing the number of Ca~+ pumps, and pharmacologically slowing the pumps already present. When the relaxation rate of the pos- terior muscle is mimicked by the addition of CPA to anterior muscle, the tension falls with a nearly identical time course over most of the force range. However, the relaxation rate de- viated at the lower end (20% maximal force to baseline), ap- proaching baseline far more slowly than in the unaltered poste- rior muscle. This effect grew more pronounced with increasing doses of CPA (Fig. 1 A). CPA seems to have a greater inhibitory effect on Ca:+ pumps at low [Ca2+], which allows a small pop- ulation of cross bridges to remain in force-producing states. Al- though these few remaining cross bridges have an almost im- perceptible effect on isometric relaxation, they generate high forces during the lengthening phase of the work loop (Fig. 1 B
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
