Abstract
The surface density of diadic junctional complexes (DJC) between
plasmalemma and terminal cisternal membrane, as well as the areas
of plasmalemmal and cisternal membrane involved in DJC, have been
determined morphometrically in external plasmalemmal envelope and
T-system of rabbit, rat, and mouse ventricular heart muscle. In all
three species, both the surface density and the plasmalemmal area
of DJC are 4- to 6-fold greater in the T-system than in the external
plasmalemmal envelope. The surface density and DJC membrane area
per unit cell volume and per unit myofibrillar volume increase in
the order rabbit less than rat congruent to mouse and are not related
simply to basal heart rate or intraventricular pressure. The results
show that if Ca$^2+$ release is a function of terminal cisterns,
then, in ventricular heart muscle, most of the Ca$^2+$ thus released
for myofibrillar activation must originate from cisterns associated
with the T-system. They make it necessary to consider the possibility
that the 20--50\% of plasmalemma in the T-system that is involved
in excitation-contraction coupling may be unavailable for other processes;
and they show that interspecies differences in surface density and
membrane area of DJC/unit cellular and myofibrillar volume correlate
with differences in Ca$^2+$- activated Ca$^2+$ release in
skinned fibers and with differences in rate of tension development
described for intact rat and rabbit ventricular muscle.
- 376173
- anatomy,
- animals,
- cell
- comparative,
- fixatives,
- gov't,
- heart
- histological
- intercellular
- junctions,
- mathematics,
- membrane,
- mice,
- myocardium,
- myofibrils,
- p.h.s.,
- rabbits,
- rats,
- research
- reticulum,
- sarcolemma,
- sarcoplasmic
- support,
- techniques,
- u.s.
- ventricles,
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