Smooth muscle cells line all of the hollow
organs of the body; the GI tract, all of the blood vessels, the bronchi
and all areas of the lung, the bladder, the urogenital tract, the
uterus, they control the diameter of the iris of the eye and even make
your hair stand on end. This tissue has such a wide distribution that
it is difficult to underestimate its importance in health and disease.
A few examples of conditions which involve alterations in the function
of smooth muscle cells include hypertension, atherosclerosis, and
asthma. These muscles have dynamic and complex mechanisms to regulate
their intracellular calcium concentration and their force of
contraction. This section of the gallery is devoted to experiments
which have helped to discover some of these mechanisms.
a and b subunits of the Na+/K+
ATPase Distribution of the a (red) and b
(green) subunits of the Na+/K+ ATPase in a smooth
muscle cell. The superimposed image demonstrates that the pump is a
heterodimer that is distributed in strands that run roughly parallel to
the long axis of the cell, although individual strands merge and
Coupling of Sarcoplasmic Reticulum
Calcium Storage to Sarcolemma Ca2+Transport
The distribution of the a subunit of the
Na+/K+ ATPase was compared to other proteins involved in ion regulation
or involved in maintenance of the cytoskeleton. The Na+/K+ ATPase was
located within 150 nm of the Na+/Ca2+ exchanger on the sarcolemma and
within 150 nm of calsequestrin in the lumen of the sarcoplasmic
reticulum, but was in a different domain of the sarcolemma than the
cytoskeletal protein vinculin.
Ca2+ Induced Ca 2+
Release in Smooth Muscle Cells
Voltage-gated Ca2+ channels
(green) on the sarcolemma are physically juxtaposed to ryanodine
receptors (red) in the SR membrane in mammalian smooth muscle cells.
This provides the structural verification that calcium-induced calcium
release can operate in mammalian smooth muscle cells.
Distribution of Active Protein Kinase C in
Single Smooth Muscle Cells
In a smooth muscle
cell at rest there is a network of active protein kinase C (green)
roughly 250 nm beneath the sarcolemma whose distribution mirrors that
of the cytoskeletal protein vinculin (red).
After stimulation with carbachol, active
protein kinase C (green) is seen throughout the myoplasm, but not in
the nucleus. Vinculin remains at the sarcolemma (red). (SMMUSC4.JPG).
Protein Kinase C has been implicated in regulating contractile force in
smooth muscle cells and its distribution to what appears to be
contractile filaments following cell activation with a muscarinic
agonist is consistent with this hypothesis.