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.
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- 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.