Smooth muscle expresses a cardiac/slow muscle isoform of the Ca2+-transport ATPase in its endoplasmic reticulum

Abstract

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.

Evidence for two isoforms of the endoplasmic-reticulum Ca2+ pump in pig smooth muscle

“…Our results are in accordance with the previous observation that the smooth-muscle ER Ca2" pump is very similar or even identical to the slow-twitch/cardiac SR isoform [4]. These SR/ER Ca2" pumps are indeed encoded by the same gene which can be alternatively spliced.…”

“…One Ca2+ pump (Mr 130 000) extrudes Ca2+ across the plasma membrane (PM) and the second (Mr 100000) reaccumulates Ca2" into an intracellular Ca2+ store, generally assumed to be the endoplasmic reticulum (ER). Recently we have demonstrated that the porcine smoothmuscle ER Ca21 pump strongly resembles the sarroplasmic reticulum (SR) Ca2+ pump of slower-twitch skeletal muscle and of cardiac muscle [4].…”

Plasma membrane calcium pumps in smooth muscle: from fictional molecules to novel inhibitors

“…The 2 pumps also differ in target size as determined by radiation inactivation. These properties led to the initial realization that the smooth muscle expressed both SERCA and PMCA pumps (Wuytack et al 1983(Wuytack et al , 1984(Wuytack et al , 1989Grover et al 1985b;Spencer et al 1991;Grover 1988). Further confirmation of these observations came from the use of SERCAand PMCA-specific antibodies (Wuytack et al 1983(Wuytack et al , 1984(Wuytack et al , 1989Spencer et al 1991;Grover 1988).…”

“…These properties led to the initial realization that the smooth muscle expressed both SERCA and PMCA pumps (Wuytack et al 1983(Wuytack et al , 1984(Wuytack et al , 1989Grover et al 1985b;Spencer et al 1991;Grover 1988). Further confirmation of these observations came from the use of SERCAand PMCA-specific antibodies (Wuytack et al 1983(Wuytack et al , 1984(Wuytack et al , 1989Spencer et al 1991;Grover 1988). Finally, the cDNA for both SERCA and PMCA pumps were cloned from smooth muscle (Carafoli 1997;Lehotsky et al 2002;Strehler et al 1991;Grover and Khan 1992;Strehler and Zacharias 2001;Shull et al 2003).…”

Expression of endoplasmic-reticulum Ca2+-pump isoforms and of phospholamban in pig smooth-muscle tissues

“…The microsomal fractions of pig cardiac muscle, antrum, pulmonary artery, aorta and liver were separated on a Laemmli-[28] type polyacrylamide gel [7.5 % (w/w) acrylamide for SERCA2 detection or 15.0% (w/w) acrylamide for PLB detection], blotted on to Immobilon-P transfer membranes (Millipore Corp., Bedford, MA, U.S.A.) and immunostained as described previously [29]. The antisera, which were elicited against a peptide-BSA conjugate, were incubated for 1 h with 0.1 % (w/v) BSA in 150 mM-NaCl/10 mM-Tris/HCI, pH 7.5, to neutralize the anti-BSA antibodies, and were subsequently added to the blot.…”