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

Abstract

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.

Loss of LMOD1 impairs smooth muscle cytocontractility and causes megacystis microcolon intestinal hypoperistalsis syndrome in humans and mice

“…It is interesting to contrast the findings reported here with several other smooth muscle-restricted actin-binding proteins that are dispensable for similar functional activity in these organs, including CNN1 (17,36), TAGLN (37), CSRP1 (38), and CALD1 (39), which would suggest that compensatory pathways exist to preserve normal organ function in the absence of each of these actin-binding proteins. On the other hand, genetic inactivation of Myh11, encoding the major thick filament protein in smooth muscle, leads to megacystis, a decrease in intestinal motility, defective contraction of the bladder, and early postnatal death, all of which are reminiscent of the Lmod1 −/− phenotype and human MMIHS (40).…”

Amino acid mutations in the caldesmon COOH-terminal functional domain increase force generation in bladder smooth muscle

“…The exact role of CaD in the regulation of contraction can be better understood using smooth muscle that lacks whole CaD or a selected functional domain of CaD. Ablation of smooth muscle CaD (h-CaD) in a previous study showed overexpression of nonmuscle CaD (l-CaD), and while the Ca 2ϩ sensitivity of force generation of h-CaD-deficient smooth muscle remained largely unchanged, the kinetic behavior during relaxation in arteries was different (20).…”

The role of caldesmon and its phosphorylation by ERK on the binding force of unphosphorylated myosin to actin

“…It is generally believed that CaD promotes relaxation [28, 29]. Albrecht et al [28], demonstrated that exogenous addition of CaD to permeabilized tissues accelerates their rate of relaxation.…”

“…Both studies reported that CaD accelerates the rate of smooth muscle relaxation and suggested that this is accomplished by inhibiting the cooperative reattachment of dephosphorylated myosin [28, 29]. In the current study, we investigated at the molecular level, the role of CaD in the binding of unphosphorylated myosin to actin.…”

“…At the whole muscle level, the role of CaD in smooth muscle relaxation has been studied by exogenous addition to permeabilized fibres [28] or more recently by studying muscle strips from CaD knockout mice [29]. Both studies reported that CaD accelerates the rate of smooth muscle relaxation and suggested that this is accomplished by inhibiting the cooperative reattachment of dephosphorylated myosin [28, 29].…”