Smooth muscle expresses a cardiac/slow muscle isoform of the Ca2+-transport ATPase in its endoplasmic reticulum.
Smooth muscle expresses in its endoplasmic reticulum an isoform of the Ca2+-transport ATPase that is very similar to or identical with that of the cardiac-muscle/slow-twitch skeletal-muscle form. However, this enzyme differs from that found in fast-twitch skeletal muscle. This conclusion is based on two independent sets of observations, namely immunological observations and phosphorylation experiments. Immunoblot experiments show that two different antibody preparations against the Ca2+-transport ATPase of cardiac-muscle sarcoplasmic reticulum also recognize the endoplasmic-reticulum/sarcoplasmic-reticulum enzyme of the smooth muscle and the slow-twitch skeletal muscle whereas they bind very weakly or not at all to the sarcoplasmic-reticulum Ca2+-transport ATPase of the fast-twitch skeletal muscle. Conversely antibodies directed against the fast-twitch skeletal-muscle isoform of the sarcoplasmic-reticulum Ca2+-transport ATPase do not bind to the cardiac-muscle, smooth-muscle or slow-twitch skeletal-muscle enzymes. The phosphorylated tryptic fragments A and A1 of the sarcoplasmic-reticulum Ca2+-transport ATPases have the same apparent Mr values in cardiac muscle, slow-twitch skeletal muscle and smooth muscle, whereas the corresponding fragments in fast-twitch skeletal muscle have lower apparent Mr values. This analytical procedure is a new and easy technique for discrimination between the isoforms of endoplasmic-reticulum/sarcoplasmic-reticulum Ca2+-transport ATPases.
Wuytack
F
F
Laboratorium voor Fysiologie, Katholieke Universiteit Leuven, Belgium.
Kanmura
Y
Y
Eggermont
J A
JA
Raeymaekers
L
L
Verbist
J
J
Hartweg
D
D
Gietzen
K
K
Casteels
R
R
D000818:Animals; D000906:Antibodies; D015153:Blotting, Western; D000252:Calcium-Transporting ATPases / Q000032:analysis* / Q000276:immunology; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D007527:Isoenzymes / Q000032:analysis* / Q000276:immunology; D009130:Muscle, Smooth / Q000201:enzymology* / Q000648:ultrastructure; D009206:Myocardium / Q000201:enzymology / Q000648:ultrastructure; D010750:Phosphoproteins / Q000276:immunology; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D013552:Swine; D014357:Trypsin
D000906:Antibodies; D007527:Isoenzymes; D010750:Phosphoproteins; D014357:Trypsin; D000252:Calcium-Transporting ATPases