Downregulation of profilin with antisense oligodeoxynucleotides inhibits force development during stimulation of smooth muscle

The actin-regulatory protein profilin has been shown to regulate the actin cytoskeleton and the motility of nonmuscle cells. To test the hypothesis that profilin plays a role in regulating smooth muscle contraction, profilin antisense or sense oligodeoxynucleotides were introduced into the canine carotid smooth muscle by a method of reversible permeabilization, and these strips were incubated for 2 days for protein downregulation. The treatment of smooth muscle strips with profilin antisense oligodeoxynucleotides inhibited the expression of profilin; it did not influence the expression of actin, myosin heavy chain, and metavinculin/vinculin. Profilin sense did not affect the expression of these proteins in smooth muscle tissues. Force generation in response to stimulation with norepinephrine or KCl was significantly lower in profilin antisense-treated muscle strips than in profilin sense-treated strips or in muscle strips not treated with oligodeoxynucleotides. The depletion of profilin did not attenuate increases in phosphorylation of the 20-kDa regulatory light chain of myosin (MLC20) in response to stimulation with norepinephrine or KCl. The increase in F-actin/G-actin ratio during contractile stimulation was significantly inhibited in profilin-deficient smooth muscle strips. These results suggest that profilin is a necessary molecule of signaling cascades that regulate carotid smooth muscle contraction, but that it does not modulate MLC20 phosphorylation during contractile stimulation. Profilin may play a role in the regulation of actin polymerization or organization in response to contractile stimulation of smooth muscle.     

Regulation of expression of avian slow myosin heavy-chain isoforms.

The slow tonic anterior latissimus dorsi (ALD) muscle of the chicken contains two isomyosins, namely SM-1 and SM-2. The proportions of the two isoforms change with age, SM-2 expression increasing at the expense of SM-1. Applying a load on the wing increases the rate and extent of SM-1 replacement. Here we have demonstrated that decreasing the load by removal of the distal portion of the wing in 1-week-old chickens had an effect opposite to that of overloading in that it slowed muscle growth and the rate of SM-1 elimination. Experimental unloading of muscles previously weighted for 1 or 3 weeks slowed the growth rate of muscles, with consequent regression of relative hypertrophy; however, it did not lead to the reexpression of SM-1 myosin. This indicates that the overload-induced changes in myosin expression are not readily reversible. Nerve section produced unexpected results, in that it advanced the normal developmental shift in myosin expression toward predominance of the SM-2 isoform, similar to the effect of muscle overload.     

Smooth muscle myosin isoform distribution and myosin ATPase in hypertrophied urinary bladder.

Hypertrophy of the urinary bladder was produced in rabbit by partial ligation of the urethra. Electrophoresis of the bladder smooth muscle myosin on highly porous (3.5-7% gradient) SDS-polyacrylamide gel revealed two heavy chain isoforms, SM-1 and SM-2 with approximate molecular weights of 204,000 and 200,000, respectively. The ratio of the SM-2 to SM-1 heavy chain is 3:1 for myosin isolated from normal bladder smooth muscle, and this ratio changes to about 1:1 in hypertrophied bladder. Despite a change in the ratio of SM-2 to SM-1, the myosin ATPase and the actin-activated ATPase activities are not altered in response to hypertrophy.     

A variant derived from rabbit aortic smooth muscle: phenotype modulation and restoration of smooth muscle characteristics in cells in culture

We examined the relationship between growth arrest of smooth muscle cells and structural changes in microfilament bundles, and also that between the structural changes and the actions of contractile agonist using a multipassagable variant cell line (SM-3) derived from rabbit aortic smooth muscle cells. The content of smooth muscle type alpha-actin increased with density-dependent growth arrest of the SM-3 cells, but was attenuated in the logarithmically growing cultures. As assessed cytochemically, the growth-arrested cells contained longitudinally oriented bundles of actin-containing microfilament and myosin-based filaments visualized with rhodamine-phalloidin and antibody against myosin light chain 20, respectively, whereas both actin- and myosin-containing structures in logarithmically growing cells showed slight, shortened, or diffused patterns. Electron microscopic examination of the growth-arrested cells revealed that the cells contained numerous and conspicuous microfilament bundles associated with many compact electron-dense bodies. In addition, pinocytotic vesicles were often found near the plasma membrane in the growth-arrested cells. SM-3 cells in the growth-arrested phase responded to prostaglandin F2 alpha (3-30 microM) and rat endothelin (0.1-1.0 microM) with a reversible contractile response, in association with monophosphorylation and/or diphosphorylation of the myosin light chain 20. However, the influence of the contractile agonists was greatly reduced during logarithmic growth. These results suggest that in the SM-3 cells in the growth-arrested phase, there is a restoration of the contractile architecture and the myosin light chain phosphorylation system. Thus, this SM-3 cell line is expected to serve as a useful model for examining biochemical and physiological phenomena of smooth muscle.     

Vascular development in early ovine gestation: carotid smooth muscle function, phenotype, and biochemical markers

Vascular smooth muscle (VSM) maturation is developmentally regulated and differs between vascular beds. The maturation and contribution of VSM function to tissue blood flow and blood pressure regulation during early gestation are unknown. The carotid artery (CA) contributes to fetal cerebral blood flow regulation and well being. We studied CA VSM contractility, protein contents, and phenotype beginning in the midthird of ovine development. CAs were collected from early (88-101 day of gestation) and late (138-150 day; term = day 150) fetal (n = 14), newborn (6-8 day old; n = 7), and adult (n = 5) sheep to measure forces in endothelium-denuded rings with KCl, phenylephrine, and ANG II; changes in cellular proteins, including total and soluble protein, actin and myosin, myosin heavy chain isoforms (MHC), filamin, and proliferating cell nuclear antigen; and vascular remodeling. KCl and phenylephrine elicited age- and dose-dependent contraction responses (P < 0.001) at all ages except early fetal, which were unresponsive. In contrast, ANG II elicited dose responses only in adults, with contractility increasing greater than fivefold vs. that shown in fetal or neonatal animals (P < 0.001). Increased contractility paralleled age-dependent increases (P < 0.01) in soluble protein, actin and myosin, filamin, adult smooth muscle MHC-2 (SM2) and medial wall thickness and reciprocal decreases (P < 0.001) in nonmuscle MHC-B, proliferating cell nuclear antigen and medial cellular density. VSM nonreceptor- and receptor-mediated contractions are absent or markedly attenuated in midgestation and increase age dependently, paralleling the transition from synthetic to contractile VSM phenotype and, in the case of ANG II, paralleling the switch to the AT(1) receptor. The mechanisms regulating VSM maturation and thus blood pressure and tissue perfusion in early development remain to be determined.     

Alterations in expression of myosin and myosin light chain kinases in response to vascular injury

Histochemical analysis ofballoon-injured rat carotid arteries revealed a coordinated expressionof nonmuscle myosin heavy chain-A and -B (NM-A and NM-B) in response toinjury. Expression of these nonmuscle myosin forms shifts from themedia to the adventitia and intima. In contrast, expression of smoothmuscle myosin heavy chain-1 (SM-1) within the media is not altered,whereas smooth muscle myosin heavy chain-2 (SM-2) expression declines.Western blotting shows a statistically significant increase inexpression of NM-A that occurs within 6 h in response to carotidinjury, suggesting this myosin form may be an appropriate experimental marker for proliferating, migrating cells in injured vessels. Nooverall change in the relative expression level of NM-B was detected,suggesting that compensatory declines in media expression are balancedby increases in the intima and adventitia. Expression of SM-1 did notchange in response to injury, whereas the expression of SM-2significantly declined between 24 h and 7 days. Expression ofmyosin light chain kinase is also negatively regulated, and the declinein its expression parallels downregulation of SM-2.

     

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

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.     

Rho GTPase signaling modulates cell shape and contractile phenotype in an isoactin-specific manner

Rho family small GTPases (Rho, Rac, and Cdc42) play an important role in cell motility, adhesion, and cell division by signaling reorganization of the actin cytoskeleton. Here, we report an isoactin-specific, Rho GTPase-dependent signaling cascade in cells simultaneously expressing smooth muscle and nonmuscle actin isoforms. We transfected primary cultures of microvascular pericytes, cells related to vascular smooth muscle cells, with various Rho-related and Rho-specific expression plasmids. Overexpression of dominant positive Rho resulted in the formation of nonmuscle actin-containing stress fibers. At the same time, -vascular smooth muscle actin (VSMactin) containing stress fibers were disassembled, resulting in a dramatic reduction in cell size. Rho activation also yielded a disassembly of smooth muscle myosin and nonmuscle myosin from stress fibers. Overexpression of wild-type Rho had similar but less dramatic effects. In contrast, dominant negative Rho and C3 exotransferase or dominant positive Rac and Cdc42 expression failed to alter the actin cytoskeleton in an isoform-specific manner. The loss of smooth muscle contractile protein isoforms in pericyte stress fibers, together with a concomitant decrease in cell size, suggests that Rho activation influences "contractile" phenotype in an isoactin-specific manner. This, in turn, should yield significant alteration in microvascular remodeling during developmental and pathologic angiogenesis. vascular smooth muscle actin; Rho GTPase; pericyte; myosin; cytoskeleton     

Cyr61 mediates the expression of VEGF, alphav-integrin, and alpha-actin genes through cytoskeletally based mechanotransduction mechanisms in bladder smooth muscle cells.

Application of cyclic strain to bladder smooth muscle (SM) cells results in profound alterations of the histomorphometry, phenotype, and function of the cells. The onset of this process is characterized by the activation of a cascade of signaling events coupled to progressive and, perhaps, interdependent changes of gene expression. In particular, externally applied cyclic stretch to cultured bladder SM cells results in the transient expression of the Cyr61 gene that encodes a cysteine-rich heparin-binding protein originally described as a proangiogenic factor capable of altering the gene programs for angiogenesis, adhesion, and extracellular matrix synthesis. In this study, we investigated the effects of mechanical stretch-induced Cyr61 on the expression of potential mechanosensitive Cyr61 target genes and the signaling pathways involved. We showed that suppression of Cyr61 expression with an adenoviral vector encoding an antisense oligonucleotide reduced mechanical strain-induced VEGF, alpha(v)-integrin, and SM alpha-actin gene expression but had no effect on the myosin heavy chain isoforms SM-1 and SM-2. Signaling pathways involving RhoA GTPase, phosphatidyl inositol 3-kinase, and cytoskeletal actin dynamics altered stretch-induced Cyr61 and Cyr61 target genes. Reciprocally, adenovirus-mediated overexpression of Cyr61 in cells cultured under static conditions increased the expression of VEGF, alpha(v)-integrin, and SM alpha-actin, as well as that of SM-1 and SM-2 isoforms, suggesting that the effects of a sustained expression of Cyr61 extend to SM specific contractile function. These effects were dependent on integrity of the actin cytoskeleton. Together, these results indicate that Cyr61 is an important determinant of the genetic reprogramming that occurs in mechanically challenged cells.     

Phasic Contractions of the Mouse Vagina and Cervix at Different Phases of the Estrus Cycle and during Late Pregnancy

Background/Aims

The pacemaker mechanisms activating phasic contractions of vaginal and cervical smooth muscle remain poorly understood. Here, we investigate properties of pacemaking in vaginal and cervical tissues by determining whether: 1) functional pacemaking is dependent on the phase of the estrus cycle or pregnancy; 2) pacemaking involves Ca²⁺ release from sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) -dependent intracellular Ca²⁺ stores; and 3) c-Kit and/or vimentin immunoreactive ICs have a role in pacemaking.

Methodology/Principal Findings

Vaginal and cervical contractions were measured in vitro, as was the distribution of c-Kit and vimentin positive interstitial cells (ICs). Cervical smooth muscle was spontaneously active in estrus and metestrus but quiescent during proestrus and diestrus. Vaginal smooth muscle was normally quiescent but exhibited phasic contractions in the presence of oxytocin or the K⁺ channel blocker tetraethylammonium (TEA) chloride. Spontaneous contractions in the cervix and TEA-induced phasic contractions in the vagina persisted in the presence of cyclopiazonic acid (CPA), a blocker of the SERCA that refills intracellular SR Ca²⁺ stores, but were inhibited in low Ca²⁺ solution or in the presence of nifedipine, an inhibitor of L-type Ca²⁺channels. ICs were found in small numbers in the mouse cervix but not in the vagina.

Conclusions/Significance

Cervical smooth muscle strips taken from mice in estrus, metestrus or late pregnancy were generally spontaneously active. Vaginal smooth muscle strips were normally quiescent but could be induced to exhibit phasic contractions independent on phase of the estrus cycle or late pregnancy. Spontaneous cervical or TEA-induced vaginal phasic contractions were not mediated by ICs or intracellular Ca²⁺ stores. Given that vaginal smooth muscle is normally quiescent then it is likely that increases in hormones such as oxytocin, as might occur through sexual stimulation, enhance the effectiveness of such pacemaking until phasic contractile activity emerges.     

Alternative splicing of smooth muscle myosin heavy chains and its functional consequences

The aim of our study was to determine the relation between alternatively spliced myosin heavy chain (MHC) isoforms and the contractility of smooth muscle. The relative amount of MHC with an alternatively spliced insert in the 5′ (amino terminal) domain was determined on the protein level using a peptide-directed antibody (a25K/50K) raised against the inserted sequence (QGPSFAY). Smooth muscle MHC isoforms of both bladder and myometrium but not nonmuscle MHC reacted with a25/50K. Using a quantitative Western-blot approach the amount of 5′-inserted MHC in rat bladder was detected to be about eightfold higher than in normal rat myometrium. The amount of heavy chain with insert was found to be decreased by about 50% in the myometrium of pregnant rats. Although bladder contained significantly more 5′-inserted MHC than myometrium, apparent maximal shortening velocities (Vmax) were comparable, being 0.138 ± 0.012 and 0.114 ± 0.023 muscle length per second of skinned bladder and normal myometrium fibers, respectively. Phosphorylation of myosin light chain 20 induced by maximal Ca²⁺/calmodulin activation was the same in bladder and myometrial fibers. These results suggest that the amount of 5′-inserted MHC is not necessarily associated with contractile properties of smooth muscle. © 1996 Wiley-Liss, Inc.     

Biomechanical and morphological properties of the multiparous ovine vagina and effect of subsequent pregnancy

Pelvic floor soft tissues undergo changes during the pregnancy. However, the degree and nature of this process is not completely characterized. This study investigates the effect of subsequent pregnancy on biomechanical and structural properties of ovine vagina. Vaginal wall from virgin, pregnant (in their third pregnancy) and parous (one year after third vaginal delivery) Swifter sheep (n = 5 each) was harvested. Samples for biomechanics and histology, were cut in longitudinal axis (proximal and distal regions). Outcome measurements describing Young’s modulus, ultimate stress and elongation were obtained from stress-strain curves. For histology samples were stained with Miller's Elastica staining. Collagen, elastin and muscle cells and myofibroblasts contents were estimated, using image processing techniques. Statistical analyses were performed in order to determine significant differences among experimental groups. Significant regional differences were identified. The proximal vagina was stiffer than distal, irrespective the reproductive status. During the pregnancy proximal vagina become more compliant than in parous (+47.45%) or virgin sheep (+64.35%). This coincided with lower collagen (−15 to −21%), higher elastin (+30 to +60%), and more smooth muscle cells (+17 to +37%). Vaginal tissue from parous ewes was weaker than of virgins, coinciding with lower collagen (−10%), higher elastin (+50%), more smooth muscle cells (+20%). It could be proposed that after pregnancy biomechanical properties of vagina do not recover to those of virgins. Since elastin has a significant influence on the compliance of soft tissues and collagen is the main “actor” regarding strength, histological analysis performed in this study justifies the mechanical behavior observed.     

Role of vimentin in smooth muscle force development

Vimentin intermediate filaments undergo spatial reorganization in cultured smooth muscle cells in response to contractile activation; however, the role of vimentin in the physiological properties of smooth muscle has not been well elucidated. Tracheal smooth muscle strips were loaded with antisense oligonucleotides (ODNs) against vimentin and then cultured for 2 days to allow for protein degradation. Treatment with vimentin antisense, but not sense, ODNs suppressed vimentin protein expression; neither vimentin antisense nor sense ODNs affected protein levels of desmin and actin. Force development in response to ACh stimulation or KCl depolarization was lower in vimentin-deficient tissues than in vimentin sense ODN- or non-ODN-treated muscle strips. Passive tension was also depressed in vimentin-depleted muscle tissues. Vimentin downregulation did not attenuate increases in myosin light chain (MLC) phosphorylation in response to contractile stimulation or basal MLC phosphorylation. In vimentin sense ODN-treated or non-ODN-treated smooth muscle strips, the desmosomal protein plakoglobin was primarily localized in the cell periphery. The membrane-associated localization of plakoglobin was reduced in vimentin-depleted muscle tissues. These studies suggest that vimentin filaments play an important role in mediating active force development and passive tension, which are not regulated by MLC phosphorylation. Vimentin downregulation impairs the structural organization of desmosomes, which may be associated with the decrease in force development. intermediate filaments; cytoskeleton; contraction; desmin     

Mechanisms of aortic smooth muscle hyporeactivity after prolonged hypoxia in rats.

The aim of this study was to determine whether the effects of hypoxia on aortic contractility reflect a decrease in smooth muscle activation [phosphorylation of the 20-kDa myosin regulatory light chain (LC(20))], the capacity for myofibrillar ATP hydrolysis (mATPase activity), or both. Our results indicate that, in endothelium-denuded aortic rings from rats exposed to hypoxia for 48 h (inspired O(2) concentration = 10%), contractions to phenylephrine and potassium chloride (KCl) are impaired compared with rings from normoxic rats. The proportion of phosphorylated to total LC(20) during aortic contraction induced by 10(-5) M phenylephrine was reduced after hypoxia (51.4 +/- 5.4% in normoxic control rats vs. 32.5 +/- 4.7% in hypoxic rats, P < 0.01). Aortic mATPase activity was also decreased (maximum ATPase rate = 29.6 +/- 3.4 and 20.7 +/- 3.7 nmol. min(-1). mg protein(-1) in control and hypoxic rats, respectively, P < 0.05). Neither proliferation nor dedifferentiation of aortic smooth muscle was evident in this model; immunostaining for smooth muscle expression of the proliferating cell nuclear antigen was negative and smooth muscle-specific isoforms of myosin heavy chains, h-caldesmon, and calponin were increased, not decreased, after hypoxic exposure. Decreased aortic reactivity after hypoxia is associated with both impairment of smooth muscle activation and diminished capacity of the actomyosin complex, once activated, to hydrolyze ATP. These changes cannot be attributed to smooth muscle dedifferentiation or to reduced contractile protein expression.     

Contractile proteins in pericytes at the blood-brain and blood-retinal barriers

Evidence from a variety of sources suggests that pericytes have contractile properties and may therefore function in the regulation of capillary blood flow. However, it has been suggested that contractility is not a ubiquitous function of pericytes, and that pericytes surrounding true capillaries apparently lack the machinery for contraction. The present study used a variety of techniques to investigate the expression of contractile proteins in the pericytes of the CNS. The results of immunocytochemistry on cryosections of brain and retina, retinal whole-mounts and immunoblotting of isolated brain capillaries indicate strong expression of the smooth muscle isoform of actin (α-SM actin) in a significant number of mid-capillary pericytes. Immunogold labelling at the ultrastructural level showed that α-SM actin expression in capillaries was exclusive to pericytes, and endothelial cells were negative. Compared to α-SM actin, non-muscle myosin was present in lower concentrations. By contrast, smooth muscle myosin isoforms, were absent. Pericytes were strongly positive for the intermediate filament protein vimentin, but lacked desmin which was consistently found in vascular smooth muscle cells. These results add support for a contractile role in pericytes of the CNS microvasculature, similar to that of vascular smooth muscle cells.     

Contraction of smooth muscle of pig airway tissues from before birth to maturity

Two heavy chains of smooth muscle myosin (MHC1 and MHC2) were identified in pig airways and parenchyma. The ratio of MHC1 to MHC2 was the same along the bronchial tree in animals of the same age, but it changed with age (mature, young, suckling, and fetus), ranging from 0.8 in the mature to 2.2 in the fetus. Stress developed in airway (trachea, bronchus, and bronchiole) and parenchymal preparations in response to carbachol and histamine (mN/mm2) was normalized for myosin content (N/mm2 myosin). Airways from sucklings always developed the greatest stress to carbachol and histamine with the rank order of maximum force (Emax) suckling greater than fetus greater than young greater than mature for carbachol in large airways. Airway ranking to histamine was similar except that Emax of fetal bronchus and bronchiole were least. In parenchymal strips, mature animals gave strong responses to carbachol and histamine compared with other age groups. Sensitivity to carbachol was increased in the suckling trachea; otherwise it did not vary with age. Chemically skinned tracheal fibers exhibited three- to fourfold greater sensitivity to Ca2+ in fetal and suckling airways compared with the older animals. It is concluded that maturation of smooth muscle occurs in the expression of myosin, in the Ca2(+)-force relationships of the contractile machinery, and in the pharmacological responsiveness of the intact smooth muscle, with the latter greatest at or soon after birth.     

Smooth muscle myosin isoform expression and LC20 phosphorylation in innate rat airway hyperresponsiveness

Four smooth muscle myosin heavy chain (SMMHC) isoforms are generated by alternative mRNA splicing of a single gene. Two of these isoforms differ by the presence [(+)insert] or absence [(-)insert] of a 7-amino acid insert in the motor domain. The rate of actin filament propulsion of the (+)insert SMMHC isoform, as measured in the in vitro motility assay, is twofold greater than that of the (-)insert isoform. We hypothesized that a greater expression of the (+)insert SMMHC isoform and greater regulatory light chain (LC(20)) phosphorylation contribute to airway hyperresponsiveness. We measured airway responsiveness to methacholine in Fischer hyperresponsive and Lewis normoresponsive rats and determined SMMHC isoform mRNA and protein expression, as well as essential light chain (LC(17)) isoforms, h-caldesmon, and alpha-actin protein expression in their tracheae. We also measured tracheal muscle strip contractility in response to methacholine and corresponding LC(20) phosphorylation. We found Fischer rats have more (+)insert mRNA (69.4 +/- 2.0%) (mean +/- SE) than Lewis rats (53.0 +/- 2.4%; P < 0.05) and a 44% greater content of (+)insert isoform relative to total myosin protein. No difference was found for LC(17) isoform, h-caldesmon, and alpha-actin expression. The contractility experiments revealed a greater isometric force for Fischer trachealis segments (4.2 +/- 0.8 mN) than Lewis (1.9 +/- 0.4 mN; P < 0.05) and greater LC(20) phosphorylation level in Fischer (55.1 +/- 6.4) than in Lewis (41.4 +/- 6.1; P < 0.05) rats. These results further support the contention that innate airway hyperresponsiveness is a multifactorial disorder in which increased expression of the fast (+)insert SMMHC isoform and greater activation of LC(20) lead to smooth muscle hypercontractility.     

Decreased velocity of shortening in arterial smooth muscle from older (28- to 31-week-old) spontaneously hypertensive rats

An increased maximum velocity of shortening (Vmax) and increased shortening ability (delta Lmax) have been reported for caudal arterial smooth muscle from 16- to 18-week-old spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto (WKY) control rats. It is known that hypertension results in hypertrophy of vascular smooth muscle. It is plausible that the faster Vmax of 16- to 18-week-old SHR arterial smooth muscle may slow down with age due to hypertrophy. The force-velocity (F-V) study done previously on caudal arterial strips from 16- to 18-week-old SHR and WKY rats was repeated on preparations from 28- to 31-week-old rats. An electromagnetic muscle lever was employed in recording force-velocity data. Analysis of these data revealed that the 28- to 31-week-old SHR (n = 7) mean F-V curve was not different from the 28- to 31-week-old WKY (n = 5) mean F-V curve (p greater than 0.05), and the shortening ability of 28- to 31-week-old SHR arterial muscle was significantly depressed compared with 28- to 31-week-old WKY arterial muscle (p less than 0.01). In conclusion, (i) although Vmax is faster in younger (16- to 18-week-old) SHR compared with age-matched WKY caudal arterial smooth muscle, SHR Vmax is not different from WKY Vmax in the older (28- to 31-week-old) rats. (ii) Shortening ability is greater in 16- to 18-week-old SHR caudal arterial strips compared with 16- to 18-week-old WKY strips, but is significantly depressed in 28- to 31-week-old SHR compared with 28- to 31-week-old WKY preparations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulmonary vascular smooth muscle: biochemical and mechanical developmental changes.

To evaluate the developmental changes in pulmonary vascular smooth muscle contractile protein content, mechanical properties, and their contribution to the high resistance characteristic of the fetal and immediate neonatal period, we studied pulmonary vessels of fetal, newborn, and adult sheep, as well as newborn and adult pigs. Strips of the second- through fifth-generation vessels were dissected, and their content of tissue total smooth muscle cell protein, myosin, and actin-to-myosin ratio were measured; the mechanical properties of the second-generation vascular strips were also studied. For all ages the smooth muscle protein and myosin content of the second-generation vessels were significantly greater than for the lower pulmonary vascular orders (P less than 0.05). The myosin content in fetal sheep (0.77 +/- 0.03 micrograms/mg wet tissue) was similar to that of the newborn (0.79 +/- 0.04) and adult (0.86 +/- 0.05). However, the smooth muscle protein content (7.94 +/- 0.21 micrograms/mg wet tissue) and the actin-to-myosin ratio of the pulmonary vascular tissue of the fetus (1.00 +/- 0.04) were lower (P less than 0.01) in the fetal than in the newborn (9.16 +/- 0.26 and 1.60 +/- 0.12) and adult (9.38 +/- 0.3 and 1.60 +/- 0.11, respectively). No differences were observed for these parameters between the newborn and adult pig. Stress (16.5 +/- 1.7 mN/mm2) and the maximum shortening capacity (13.0 +/- 1.5% of optimal length) in the newborn pulmonary vascular strips were significantly greater than for the fetus (6.8 +/- 1.4 and 5.9 +/- 1.0, respectively) but similar to those of the adult sheep.(ABSTRACT TRUNCATED AT 250 WORDS)