AJP - Heart and Circulatory Physiology, Vol 253, Issue 6 1484-H1491, Copyright © 1987 by American Physiological Society
Contractile function of isolated young and adult rat heart cells
R. A. Haworth, P. Griffin, B. Saleh, A. B. Goknur and H. A. Berkoff
Department of Surgery, University of Wisconsin Clinical Science Center, Madison 53792.
The stimulated contractile function of aerobic isolated adult rat heart
cells was assessed by laser light diffraction. Cells were maintained for up
to 8 h by attachment to a cover slip and continuous perfusion in a chamber
on the microscope stage. On stimulation such cells beat as though
unattached. Cells showed a negative staircase which was reduced by
increasing Ca or isoproterenol. Ryanodine caused a positive staircase on
stimulation, which was enhanced by increasing Ca or isoproterenol or by
using cells from younger rats. For beats of constant contraction duration,
there was a linear relationship between the magnitude of cell shortening
and the velocity of shortening, independent of the concentration of
extracellular Ca. We conclude the following. 1) The beat characteristics of
isolated cells are very similar to those of papillary muscle. 2) Attachment
of cells need not alter their unloaded shortening characteristics. 3) Cells
appear to contract against an internal load, to an extent determined by the
degree of myofilament activation. 4) Cells from young rats require less
extracellular Ca than those from adult rats for the same beat magnitude.
