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Journal of Experimental Biology, Vol 202, Issue 7 881-890, Copyright © 1999 by Company of Biologists

JOURNAL ARTICLES

The sarcoplasmic reticulum plays a major role in isometric contraction in atrial muscle of yellowfin tuna

HA Shiels, EV Freund, AP Farrell and BA Block
Simon Fraser University, Department of Biological Sciences, Burnaby, British Columbia, Canada V5A 1S6 and Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA. hollys@sfu.ca.

We used an isometric muscle preparation to test the hypothesis that yellowfin tuna Thunnus albacares utilize the intracellular Ca2+ storage sites of the sarcoplasmic reticulum (SR) during routine contractions. Ryanodine (a blocker of SR Ca2+ release) reduced the force of contraction by approximately 50 % and the rates of contraction and relaxation by 60 % in yellowfin tuna atrium. High levels of adrenaline were unable to ameliorate the effects of ryanodine. We conclude that the SR is active in contributing Ca2+ to force development at physiological contraction frequencies. Further, we suggest that, by using intracellular Ca2+ cycling, the yellowfin tuna is able to increase the maximum contraction frequency of its cardiac muscle beyond that of most other fishes.




© The Company of Biologists Ltd 1999