Is Myosin Phosphorylation Sufficient to Regulate Smooth Muscle Contraction?

Pfitzer, Gabriele; Schroeter, Mechthild M.; Hasse, Veronika; Ma, Jun; Rösgen, Klaus-Henning; Rösgen, S.; Smyth, Neil

doi:10.1007/0-387-24990-7_24

Cited by 5 publications

(10 citation statements)

References 34 publications

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“…In bladder the difference between KO and WT was even less, and the Ca 2+ dependence of active force was steeper than that of aorta. This is in contrast to previous studies where an increase in force at low Ca 2+ was observed when h-CaD was extracted from skinned taenia coli, and the change was partially reversed by reconstitution of CaD [45,54]. We believe that, although for visceral smooth muscle there might indeed be a more robust CaD effect than in vascular smooth muscle, such an effect was masked by the up-regulation of l-CaD in the KO tissues, rendering a decreased net difference in our experiments.…”

Section: Discussioncontrasting

confidence: 92%

Ablation of smooth muscle caldesmon affects the relaxation kinetics of arterial muscle

Guo

Huang

Semba

et al. 2012

Pflugers Arch - Eur J Physiol

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Smooth muscle caldesmon (h-CaD) is an actin- and myosin-binding protein that reversibly inhibits the actomyosin ATPase activity in vitro. To test the function of h-CaD in vivo, we eliminated its expression in mice. The h-CaD-null animals appeared normal and fertile, although the litter size was smaller. Tissues from the homozygotes lacked h-CaD and exhibited up-regulation of the non-muscle isoform, l-CaD, in visceral, but not vascular tonic smooth muscles. While the Ca2+-sensitivity of force generation of h-CaD-deficient smooth muscle remained largely unchanged, the kinetic behavior during relaxation in arteries was different. Both intact and permeabilized arterial smooth muscle tissues from the knockout animals relaxed more slowly than those of the wild-type. Since this difference occurred after myosin dephosphorylation was complete, the kinetic effect most likely resulted from slower detachment of unphosphorylated cross-bridges. Detailed analyses revealed that the apparently slower relaxation of h-CaD-null smooth muscle was due to an increase in the amplitude of a slower component of the biphasic tension decay. While the identity of this slower process has not been unequivocally determined, we propose it reflects a thin-filament state that elicits fewer re-attached cross-bridges. Our finding that h-CaD modulates the rate of smooth muscle relaxation clearly supports a role in the control of vascular tone.

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Section: Discussioncontrasting

confidence: 92%

Ablation of smooth muscle caldesmon affects the relaxation kinetics of arterial muscle

Guo

Huang

Semba

et al. 2012

Pflugers Arch - Eur J Physiol

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“…8 ). In contrast to CaD-extracted Triton X-100–skinned taenia coli fibers ( Pfitzer et al, 2005 ), Cald1 −/− strips did not contract in the absence of Ca 2+ (pCa >8). The threshold pCa for eliciting a contraction was lower in KO than in WT (P < 0.01; Fig.…”

Section: Resultsmentioning

confidence: 86%

“…As the impact of CaD on smooth muscle contraction has been investigated in Triton S-100–skinned fibers ( Pfitzer et al, 1993 ; Malmqvist et al, 1996 ; Albrecht et al, 1997 ; Pfitzer et al, 2005 ), we first investigated the contractile properties in such skinned strips from urinary bladder prestretched to 1.5 L 0 ( Fig. 8 ).…”

Section: Resultsmentioning

confidence: 99%

“…However, force and RLC phosphorylation are frequently uncoupled, e.g., during sustained contractions. This indicates that additional regulatory mechanisms may be present ( Morgan and Gangopadhyay, 2001 ; Pfitzer et al, 2005 ). The protein caldesmon (CaD) is a candidate for such an actin-associated regulatory mechanism (reviewed in Chalovich et al, 1998 ; Marston et al, 1998 ; Gusev, 2001 ; Wang, 2001 ).…”

Section: Introductionmentioning

confidence: 99%

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Caldesmon ablation in mice causes umbilical herniation and alters contractility of fetal urinary bladder smooth muscle

Pütz

Barthel

Frohn

et al. 2021

Journal of General Physiology

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The actin-, myosin-, and calmodulin-binding protein caldesmon (CaD) is expressed in two splice isoforms: h-CaD, which is an integral part of the actomyosin domain of smooth muscle cells, and l-CaD, which is widely expressed and is involved in many cellular functions. Despite extensive research for many years, CaD's in vivo function has remained elusive. To explore the role of CaD in smooth muscle contraction in vivo, we generated a mutant allele that ablates both isoforms. Heterozygous animals were viable and had a normal life span, but homozygous mutants died perinatally, likely because of a persistent umbilical hernia. The herniation was associated with hypoplastic and dysmorphic abdominal wall muscles. We assessed mechanical parameters in isometrically mounted longitudinal strips of E18.5 urinary bladders and in ring preparations from abdominal aorta using wire myography. Ca2+ sensitivity was higher and relaxation rate was slower in Cald1−/− compared with Cald1+/+ skinned bladder strips. However, we observed no change in the content and phosphorylation of regulatory proteins of the contractile apparatus and myosin isoforms known to affect these contractile parameters. Intact fibers showed no difference in actin and myosin content, regardless of genotype, although KCl-induced force tended to be lower in homozygous and higher in heterozygous mutants than in WTs. Conversely, in skinned fibers, myosin content and maximal force were significantly lower in Cald1−/− than in WTs. In KO abdominal aortas, resting and U46619 elicited force were lower than in WTs. Our results are consistent with the notion that CaD impacts smooth muscle function dually by (1) acting as a molecular brake on contraction and (2) maintaining the structural integrity of the contractile machinery. Most importantly, CaD is essential for resolution of the physiological umbilical hernia and ventral body wall closure.

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“…the so called latch state (Dillon et al 1981). Although several models have been put forward to account for the latch state it is still a matter of debate how it is regulated (Hai and Murphy 1989; Somlyo et al 1988; Butler and Siegman 1998; Vyas et al 1994; Pfitzer et al 2005). …”

Section: Introductionmentioning

confidence: 99%

New insights into myosin phosphorylation during cyclic nucleotide-mediated smooth muscle relaxation

Puetz

Schroeter

Piechura

et al. 2012

J Muscle Res Cell Motil

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Nitrovasodilators and agonists, via an increase in intracellular cyclic nucleotide levels, can induce smooth muscle relaxation without a concomitant decrease in phosphorylation of the regulatory light chains (RLC) of myosin. However, since cyclic nucleotide-induced relaxation is associated with a decrease in intracellular [Ca2+], and hence, a decreased activity of MLCK, we tested the hypothesis that the site responsible for the elevated RLC phosphorylation is not Ser19. Smooth muscle strips from gastric fundus were isometrically contracted with ET-1 which induced an increase in monophosphorylation from 9 ± 1 % under resting conditions (PSS) to 36 ± 1 % determined with 2D-PAGE. Electric field stimulation induced a rapid, largely NO-mediated relaxation with a half time of 8 s, which was associated with an initial decline in RLC phosphorylation to 18 % within 2 s and a rebound to 34 % after 30 s whereas relaxation was sustained. In contrast, phosphorylation of RLC at Ser19 probed with phosphospecific antibodies declined in parallel with force. LC/MS and western blot analysis with phosphospecific antibodies against monophosphorylated Thr18 indicate that Thr18 is significantly monophosphorylated during sustained relaxation. We therefore suggest that (i) monophosphorylation of Thr18 rather than Ser19 is responsible for the phosphorylation rebound during sustained EFS-induced relaxation of mouse gastric fundus, and (ii) that relaxation can be ascribed to dephosphorylation of Ser19, the site considered to be responsible for regulation of smooth muscle tone.

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Is Myosin Phosphorylation Sufficient to Regulate Smooth Muscle Contraction?

Cited by 5 publications

References 34 publications

Ablation of smooth muscle caldesmon affects the relaxation kinetics of arterial muscle

Ablation of smooth muscle caldesmon affects the relaxation kinetics of arterial muscle

Caldesmon ablation in mice causes umbilical herniation and alters contractility of fetal urinary bladder smooth muscle

New insights into myosin phosphorylation during cyclic nucleotide-mediated smooth muscle relaxation

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