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The Biological Bulletin, Vol 190, Issue 3 385-395, Copyright © 1996 by Marine Biological Laboratory

PHYSIOLOGY AND BIOCHEMISTRY

Comparison of Temperature Effects on Heart Performance of the Dungeness Crab, Cancer magister, in vitro and in vivo

B. De Wachter and J. L. Wilkens
Department of Biological Sciences, University of Calgary, Calgary T2N 1N4, Alberta, Canada

A large percentage of physiological studies are based on isolated components of complex systems, but the question can always be posed, are the responses the same in isolation as when these components are under the homeostatic controls that exist in vivo? For cardiac performance in Cancer magister, the responses to temperature variation over the range 4{deg} to 20{deg}C are different in semi-isolated hearts than in intact animals. Cardiac performance in semi-isolated hearts was measured with a pressure transducer, a flow transducer, and electromyogram (EMG) electrodes, and in intact animals with pulsed Doppler flow probes. Heart rate increase in semi-isolated hearts was about one-third of that in intact animals. The cardiac output of semi-isolated hearts decreased with increasing temperature, whereas that of intact animals increased. Stroke volume decreased linearly in semi-isolated hearts. In intact animals, stroke volume decreased from 4{deg} to 12{deg}C, but remained relatively stable from 12{deg} to 20{deg}C. The ventricular pressure and the EMG amplitude of semi-isolated hearts both decreased with increasing temperature. Double systolic contractions appeared both in semi-isolated hearts and in intact animals in the temperature range 13{deg} to 20{deg}C; this may represent a compensatory mechanism at extreme temperatures. The difference in cardiac performance between intact crabs and semi-isolated hearts reflects, almost certainly, extrinsic control in intact animals, including modulation by cardioregulatory nerves or neurohormonal modulation of the cardiac ganglion, myocardial contractility or changes in outflow resistance.


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