PT  - JOURNAL ARTICLE
AU  - Shiels, H.A.
AU  - Freund, E.V.
AU  - Farrell, A.P.
AU  - Block, B.A.
TI  - The sarcoplasmic reticulum plays a major role in isometric contraction in atrial muscle of yellowfin tuna
DP  - 1999 Apr 01
TA  - Journal of Experimental Biology
PG  - 881--890
VI  - 202
IP  - 7
4099  - http://jeb.biologists.org/content/202/7/881.short
4100  - http://jeb.biologists.org/content/202/7/881.full
SO  - J. Exp. Biol.1999 Apr 01; 202
AB  - 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.