Abstract
Cardiac muscle sarcoplasmic reticulum appears to contain channel-like
structures that render the membrane permeable to small univalent
ions. Canine heart microsomes fractionated according to buoyant density
were examined by Millipore filtration, light scattering, and membrane
potential m easurements. Enzymatic analysis and measurement of D-glucose
permeation and Na/Ca exchange systems indicated two membrane fractions
suitable for the permeability studies, one enriched in surface membranes
with a buoyant density of 1.04-1.11 (10-25\% sucrose) and one enriched
in sarcoplasmic reticulum with a buoyant density of 1.13-1.15 (30-34\%
sucrose). Surface membrane vesicles impermeable to 3Hsucrose were
largely impermeable to K$^+$, Na$^+$, and Cl$^-$, while
sarcoplasmic reticulum vesicles impermeable to 3Hsucrose were readily
permeable to K$^+$, Na$^+$, H$^+$, and Cl$^-$. Sarcoplasmic
reticulum vesicles were essentially impermeable to Ca$^2+$, Mg2+,
choline+, gluconate-, 1,4-piperazinediethanesulfonic acid (Pipes-),
and D-glucose. These results suggest that cardiac muscle sarcoplasmic
reticulum contains structures that facilitate the movement of small
univalent ions. A possible function of these putative ion-conducting
structures may be to allow rapid ion fluxes to counter electrogenic
Ca$^2+$ fluxes across sarcoplasmic reticulum during cardiac muscle
contraction and relaxation.
- 7085644
- active,
- animals,
- biological
- chlorides,
- concentration,
- dogs,
- electron,
- gov't,
- hydrogen-ion
- intracellular
- kinetics,
- membranes,
- microscopy,
- microsomes,
- myocardium,
- p.h.s.,
- permeability,
- potassium,
- research
- reticulum,
- sarcoplasmic
- sodium,
- support,
- transport,
- u.s.
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