Length-dependent activation in intact ferret hearts: a study of
steady-state calcium-stress-strain interrelations.
Stennett, Richard, Kazuhide Ogino, James P. Morgan, and Daniel
Burkhoff.
Department of Anesthesiology, and Division of Circulatory
Physiology, Department of Medicine, Columbia University, 630 W. 168th
St., New York, NY 10032 and Division of Cardiology, Beth Israel
Hospital, Boston, MA
APStracts 2:0492H, 1995.
We examined the steady-state stress-strain relationships and the
steady-state stress-intracellular calcium ([Ca2+]i) relationship in
intact ferret hearts and compared these to previously published
analogous relationships in skinned and intact muscle. Langendorff
-perfused ferret hearts were treated with ryanodine and tetanized by
rapid stimulation to create steady-state conditions. [Ca2+]i was
measured concurrently by macroinjected aequorin. Over a range of
volumes corresponding to strains between 1.0 and 0.75, steady-state
stress decreased by 33% when saturating levels of perfusate calcium
were used indicating the degree to which physical factors contribute
to the Frank-Starling relationship. The steady-state stress-[Ca2+]i
relationship was sigmoidal with a mean Hill coefficient (n) of
4.91+/-0.29 at a strain of 1.0, and the [Ca2+]i required for half
-maximal activation (K 1/2) was 0.41+/-0.03 [mu]mol/L. K 1/2 increased
and n decreased with decreasing strains. These results are similar to
those observed in intact muscle, but differ quantitatively from
results obtained in isolated skinned preparations. Based upon these
results, we suggest that whole heart function can be related to
average sarcomere function without the need for complex models of
ventricular structure.
Received 2 August 1995; accepted in final form 5 October 1995.
APS Manuscript Number H727-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95