Abstract
Since the role of sarcoplasmic reticulum (SR) in the E-C coupling
of mammalian atrial cells has long been a subject of debate, biochemical,
electrophysiological and immunological assays were performed in order
to define and compare the properties of the Ca$^2+$-release channel-ryanodine
receptor (RyR)-from atrial and ventricular tissues. Cardiac SR preparations
from human, canine and ovine tissues were compared using (3)Hryanodine
binding, channel reconstitution into planar lipid bilayers and Western
blot analysis involving RyR antibodies. (3)Hryanodine binding assays
revealed a K(d)value of; 2.5 n M for all investigated cardiac tissues.
Bound (3)Hryanodine was Ca$^2+$-dependent with similar EC(50)values
of 0.43, 0.49 and 0.79 microM for human atrium, canine ventricle
and ovine atrium, respectively. However the density of binding sites
was 4.5 times lower in atrial than in ventricular tissues. Beyond
the presence of selective K$^+$channels (gamma=188 pS) recorded
in the SR enriched fraction of human atrium, the activity of a large
conducting (gamma=671 pS) cationic channel was also observed. The
latter displayed typical characteristics of Ca$^2+$-release channels
which were activated by 10 microM free Ca$^2+$ and 2 m M ATP.
Western blot analysis revealed the presence of the RyR2 isoform in
atrial and ventricular samples whereas no immunoreactivity was detected
with specific RyR1 and RyR3 antibodies. Our results, obtained at
the molecular level, are consistent with the presence of functional
SR in human atrial cells. The human atrial Ca$^2+$-release channel
displays binding and regulating properties typical of the RyR2 isoform.
- 11040108
- aged,
- animals,
- atria,
- bilayers,
- blotting,
- calcium
- calcium,
- cardiac,
- channel
- channel,
- channels,
- child,
- comparative
- conductivity,
- dogs,
- elapid
- electric
- female,
- gating,
- gov't,
- heart
- humans,
- ion
- isoforms,
- lipid
- magnesium,
- male,
- middle
- muscle
- myocytes,
- non-u.s.
- potassium
- potassium,
- protein
- proteins,
- rabbits,
- receptor
- red,
- release
- research
- reticulum,
- ruthenium
- ryanodine
- ryanodine,
- sarcoplasmic
- sheep,
- species
- specificity,
- study,
Users
Please
log in to take part in the discussion (add own reviews or comments).