COVID-19-induced changes in the workplace, psychosocial work environment and employee well-being: a longitudinal study.

BACKGROUND: In many workplaces, the coronavirus disease 2019 pandemic changed work arrangements, but there is scarce longitudinal evidence on whether psychosocial work environment and employee well-being were affected. AIMS: To examine the psychosocial work environment and employee well-being before, during and after the pandemic in relation to pandemic-induced changes (working from home, change to other tasks and team reorganization). METHODS: Survey data from a cohort of 20 944 public sector employees in Finland were collected before (2016-2018), during (2020) and after the pandemic (2022). Multilevel linear and logistic regression was used to examine group differences between the before-during and during-after periods of the pandemic. RESULTS: Working from home was associated with a small but favourable change in worktime control, organizational justice and social capital (scale 1-5) during the pandemic and after the pandemic (marginal mean difference ranging from 0.02 to 0.09 with 95% confidence intervals [CIs] from 0.01 to 0.10). There was a post-pandemic increase in work time control, even among participants with a transfer into other tasks (0.11, 95% CI 0.07, 0.14) or team reorganization (0.06, 95% CI 0.02, 0.10). The decline in self-rated work ability (scale 0-10) before and during the pandemic was greater in those transferred into other tasks (-0.10, 95% CI -0.13, -0.06) than in those not (-0.05, 95% CI -0.06, -0.04). CONCLUSIONS: Working from home during the pandemic was accompanied by small favourable changes in the psychosocial work environment during the pandemic, whereas transition to different tasks was associated with a decline in self-rated work ability.

Psychosocial factors associated with work disability in men and women with diabetes: a pooled analysis of three occupational cohort studies.

AIMS: To examine the extent to which adverse psychosocial factors, such as living alone, psychological distress, job strain and low support from supervisor, increase the risk of work disability (sickness absence and disability pension) among employees with diabetes. METHODS: In this pooled analysis of individual-participant data from three occupational cohort studies (the Finnish Public Sector Study, the British Whitehall II study, and the French GAZEL study), 1088 women and 949 men with diabetes were followed up to determine the duration (number of days) and frequency (number of spells) of work disability. The mean follow-up periods were 3.2 years in the GAZEL study, 4.6 years in the Whitehall II study and 4.7 years in the Finnish Public Sector Study. Psychosocial factors and potential confounding factors were assessed at baseline using standard questionnaires. Study-specific estimates were pooled using fixed-effects meta-analysis. RESULTS: In analysis adjusted for sociodemographic factors, health behaviours and comorbidities, participants with psychological distress had longer (rate ratio 1.66; 95% CI 1.31-2.09) and more frequent absences (rate ratio 1.33; 95% CI 1.19-1.49) compared with those with no psychological distress. Job strain was associated with slightly increased absence frequency (rate ratio 1.19 95% CI 1.05-1.35), but not with absence duration. Living alone and low supervisor support were not associated with absence duration or frequency. We observed no sex differences in these associations. CONCLUSIONS: Psychological distress was associated with increased duration and frequency of work disability among employees with diabetes. Job strain was associated with increased absence frequency but not with absence duration.

Postanesthetic death in a cat with myopathy.

There are few reports of naturally occurring muscular dystrophy in domestic animals. Herein, we describe a case of muscular dystrophy in a 4-year-old neutered male American domestic shorthair cat that died unexpectedly following anesthesia for an elective surgical procedure. Macroscopic muscular hypertrophy and histologic evidence of myofiber size variation, mineralization, myofiber degeneration, and necrosis were compatible with a diagnosis of muscular dystrophy. Extensive endomysial fibrosis was noted histologically in the diaphragm. A complete absence of dystrophin protein in Western blot confirmed the diagnosis of Duchenne muscular dystrophy. Immunofluorescence microscopy revealed reduced levels of dystrophin-associated proteins and an upregulation of utrophin at the sarcolemma. Anesthetic deaths can occur in dystrophin-deficient cats, and therefore muscular dystrophy and the associated cardiomyopathy should be considered in the differential diagnoses for perianesthetic death in cats.

Sickness absence among Finnish special and general education teachers.

BACKGROUND: Although teaching is considered a high-stress profession, research on stress-related outcomes among teachers, such as absence from work due to illness (i.e. sickness absence), remains scarce. It is possible that teachers are not a homogeneous group but include subgroups with particularly high risk of sickness absence, such as special education teachers. AIMS: To examine differences in sickness absence rates between special and general education teachers in a large cohort of 2291 Finnish lower secondary school teachers. METHODS: Register data on teachers' job titles, sociodemographic characteristics and sickness absence were obtained from 10 municipal employers' registers. Indices of sickness absence included rates of short-term (1-3 days) and long-term (>3 days) absence spells during 2003-05. RESULTS: With multi-level models adjusted for individual- and school-level covariates, we found that although the absolute level of sickness absence was higher among women than among men, male special education teachers were at a 1.36-fold (95% CI: 1.15-1.61) increased risk of short-term and a 1.33-fold (95% CI: 1.01-1.76) increased risk of long-term sickness absence compared with male teachers in general education. Among women, there were no differences in sickness absence between special and general education teachers. CONCLUSIONS: Compared to male teachers in general education, male teachers in special education appear to have an excess risk of absence from work due to illness. Future studies should examine the causes for this excess risk and determine the need for preventive interventions.

Effect of intravesical instillations on the human complement factor H related protein (BTA stat) test.

OBJECTIVES: The BTA stat is a rapid, non-invasive, qualitative urine test that detects bladder tumor-associated antigen (human complement factor H related protein) in urine. The sensitivity of this test is superior to that of urine cytology in detecting primary and recurrent tumors of the urinary bladder. Intravesical instillations are widely used to avoid recurrences and even progression. The objective of this study was to evaluate the effect of intravesical treatments on the BTA stat Test. METHODS: 501 consecutive patients followed up for bladder cancer were studied, of which 490 were eligible for analysis. Three hundred and twenty-seven (66.7%) of the patients had no history of intravesical treatments, whereas the remaining 163 (33.3%) had received treatments: 66 (40.5%) at the time of evaluation. A voided urine sample was obtained prior to cystoscopy and split for culture and BTA stat testing. The overall sensitivity and specificity were calculated and compared to the patients with no, past and present instillations. RESULTS: The overall sensitivity for the BTA stat Test was 56.6%, and the specificity was 76.4%. The specificity of the BTA stat Test was 80.7, 70.7 and 65.3% in those with no, past or present intravesical instillation treatments, respectively. The difference in specificity between those with no and present instillations was significant (p = 0.023), whereas the notable difference between those with no and past instillations did not reach significance (p = 0.076), nor was the difference between patients with past and present instillations significant (p = 0.558). Present instillation of mitomycin C had the strongest adverse effect on the test as the specificity was only 25.0%, whereas past treatment did not interfere with testing. The adverse effect of BCG treatment on testing extended. CONCLUSION: The overall specificity of the test is decreased in patients receiving intravesical treatments, whereas past treatments did not interfere with testing in general. However, the adverse effect of BCG on testing seems to extend, and therefore it is suggested that the BTA stat Test should not be used in patients having received BCG, and in those with present instillation of any type.

Differential Vicia villosa agglutinin reactivity identifies three distinct dystroglycan complexes in skeletal muscle.

We present evidence for the expression of three alpha-dystroglycan glycoforms in skeletal muscle cells, including two minor glycoforms marked by either patent or latent reactivity with the N-acetylgalactosamine-specific lectin Vicia villosa agglutinin. Both minor glycoforms co-isolated with beta-dystroglycan, but not with other dystrophin/utrophin-glycoprotein complex components, suggesting that they may perform distinct or modified cellular functions. We also confirmed that both patent and latent V. villosa agglutinin-reactive alpha-dystroglycan glycoforms are expressed in C2C12 myotubes. However, we found that the combined effect of saturating concentrations of V. villosa agglutinin and laminin-1 were strictly additive with respect to acetylcholine receptor cluster formation in C2C12 myotubes, which suggests that laminin-1 and V. villosa agglutinin do not compete for the same binding site on the cell surface. Finally, although beta-N-acetylhexosaminidase digestion dramatically inhibited agrin-, V. villosa agglutinin-, and laminin-1-induced acetylcholine receptor clustering in C2C12 myotubes, treatment with this enzyme had no effect on the amount of alpha-dystroglycan that was bound to V. villosa agglutinin-agarose. We conclude that alpha-dystroglycan is not the V. villosa agglutinin receptor implicated in acetylcholine receptor cluster formation. However, our data provide new support for the hypothesis that different glycoforms of alpha-dystroglycan may perform distinct functions even within the same cell.

Binding of dystrophin's tandem calponin homology domain to F-actin is modulated by actin's structure.

Dystrophin has been shown to be associated in cells with actin bundles. Dys-246, an N-terminal recombinant protein encoding the first 246 residues of dystrophin, includes two calponin-homology (CH) domains, and is similar to a large class of F-actin cross-linking proteins including alpha-actinin, fimbrin, and spectrin. It has been shown that expression or microinjection of amino-terminal fragments of dystrophin or the closely related utrophin resulted in the localization of these protein domains to actin bundles. However, in vitro studies have failed to detect any bundling of actin by either intact dystrophin or Dys-246. We show here that the structure of F-actin can be modulated so that there are two modes of Dys-246 binding, from bundling actin filaments to only binding to single filaments. The changes in F-actin structure that allow Dys-246 to bundle filaments are induced by covalent modification of Cys-374, proteolytic cleavage of F-actin's C-terminus, mutation of yeast actin's N-terminus, and different buffers. The present results suggest that F-actin's structural state can have a large influence on the nature of actin's interaction with other proteins, and these different states need to be considered when conducting in vitro assays.

The dystrophin complex forms a mechanically strong link between the sarcolemma and costameric actin.

The absence of dystrophin complex leads to disorganization of the force-transmitting costameric cytoskeleton and disruption of sarcolemmal membrane integrity in skeletal muscle. However, it has not been determined whether the dystrophin complex can form a mechanically strong bond with any costameric protein. We performed confocal immunofluorescence analysis of isolated sarcolemma that were mechanically peeled from skeletal fibers of mouse hindlimb muscle. A population of gamma-actin filaments was stably associated with sarcolemma isolated from normal muscle and displayed a costameric pattern that precisely overlapped with dystrophin. However, costameric actin was absent from all sarcolemma isolated from dystrophin-deficient mdx mouse muscle even though it was localized to costameres in situ. Vinculin, alpha-actinin, beta-dystroglycan and utrophin were all retained on mdx sarcolemma, indicating that the loss of costameric actin was not due to generalized membrane instability. Our data demonstrate that the dystrophin complex forms a mechanically strong link between the sarcolemma and the costameric cytoskeleton through interaction with gamma-actin filaments. Destabilization of costameric actin filaments may also be an important precursor to the costamere disarray observed in dystrophin-deficient muscle. Finally, these methods will be broadly useful in assessing the mechanical integrity of the membrane cytoskeleton in dystrophic animal models lacking other costameric proteins.

Utrophin lacks the rod domain actin binding activity of dystrophin.

We previously identified a cluster of basic spectrin-like repeats in the dystrophin rod domain that binds F-actin through electrostatic interactions (Amann, K. J., Renley, B. A., and Ervasti, J. M. (1998) J. Biol. Chem. 273, 28419-28423). Because of the importance of actin binding to the presumed physiological role of dystrophin, we sought to determine whether the autosomal homologue of dystrophin, utrophin, shared this rod domain actin binding activity. We therefore produced recombinant proteins representing the cluster of basic repeats of the dystrophin rod domain (DYSR11-17) or the homologous region of the utrophin rod domain (UTROR11-16). Although UTROR11-16 is 64% similar and 41% identical to DYSR11-17, UTROR11-16 (pI = 4. 86) lacks the basic character of the repeats found in DYSR11-17 (pI = 7.44). By circular dichroism, gel filtration, and sedimentation velocity analysis, we determined that each purified recombinant protein had adopted a stable, predominantly alpha-helical fold and existed as a highly soluble monomer. DYSR11-17 bound F-actin with an apparent K(d) of 7.3 +/- 1.3 microM and a molar stoichiometry of 1:5. Significantly, UTROR11-16 failed to bind F-actin at concentrations as high as 100 microM. We present these findings as further support for the electrostatic nature of the interaction of the dystrophin rod domain with F-actin and suggest that utrophin interacts with the cytoskeleton in a manner distinct from dystrophin.

Dystrophin binding to nonmuscle actin.

We purified actin from bovine brain by DNase I affinity chromatography in order to compare the binding of dystrophin to muscle actin with its binding to nonmuscle actin. While both beta- and gamma-nonmuscle actins are expressed in brain, Western blot analysis with isoform-specific antibodies indicated that our purified brain actin was exclusively the gamma-isoform. The recombinant amino-terminal, actin-binding domain of dystrophin bound to muscle and brain actin in a saturable manner (approximately 1 mol/mol actin) with similar Kd values of 13.7+/-3.5 and 10.6+/-3.7 microM, respectively. We further demonstrate that intact dystrophin in the dystrophin-glycoprotein complex bound with equal avidity to muscle and brain F-actin. These data argue that a preferential binding of dystrophin to nonmuscle actin is not the basis for its targeting to the muscle cell plasmalemma but do support the hypothesis that dystrophin is capable of interacting with filamentous actin in nonmuscle tissues.

A cluster of basic repeats in the dystrophin rod domain binds F-actin through an electrostatic interaction.

The dystrophin rod domain is composed of 24 spectrin-like repeats and was thought to act mainly as a flexible spacer between the amino-terminal actin binding domain and carboxyl-terminal membrane-associated domains. We previously demonstrated that a fragment of the dystrophin rod domain also binds F-actin. However, the nature and extent of rod domain association with F-actin is presently unclear. To begin addressing these questions, we characterized two recombinant proteins representing adjacent regions of the dystrophin rod. DYS1416 (amino acids 1416-1880) bound F-actin with a Kd of 14.2 +/- 5.2 microM and a stoichiometry of 1 mol:mol of actin. However, DYS1030 (amino acids 1030-1494) failed to bind F-actin, suggesting that not all rod domain repeats are capable of binding F-actin. Interestingly, DYS1416 corresponds to a unique region of the dystrophin rod rich in basic amino acids, whereas DYS1030 is composed mainly of acidic repeats. This observation suggested that DYS1416 may interact with acidic actin filaments through an electrostatic interaction. Supporting this hypothesis, actin binding by DYS1416 was dramatically inhibited by increasing ionic strength. We suggest that electrostatic interactions between basic spectrin-like repeats and actin filaments may contribute to the actin binding activity of other members of the actin cross-linking protein family.

Differential heparin sensitivity of alpha-dystroglycan binding to laminins expressed in normal and dy/dy mouse skeletal muscle.

The alpha-dystroglycan binding properties of laminins extracted from fully differentiated skeletal muscle were characterized. We observed that the laminins expressed predominantly in normal adult rat or mouse skeletal muscle bound alpha-dystroglycan in a Ca2+-dependent, ionic strength-sensitive, but heparin-insensitive manner as we had observed previously with purified placental merosin (Pall, E. A., Bolton, K. M., and Ervasti, J. M. 1996 J. Biol. Chem. 271, 3817-3821). Rat skeletal muscle laminins partially purified by heparin-agarose affinity chromatography also bound alpha-dystroglycan without sensitivity to heparin. We also confirm previous studies of dystrophic dy/dy mouse skeletal muscle showing that the alpha2 chain of merosin is reduced markedly and that the laminin alpha1 chain is not up-regulated detectably. However, we further observed a quantitative decrease in the expression of laminin beta/gamma chain immunoreactivity in alpha2 chain-deficient dy/dy skeletal muscle and reduced alpha-dystroglycan binding activity in laminin extracts from dy/dy muscle. Most interestingly, the alpha-dystroglycan binding activity of residual laminins expressed in merosin-deficient dy/dy skeletal muscle was inhibited dramatically (69 +/- 19%) by heparin. These results identify a potentially important biochemical difference between the laminins expressed in normal and dy/dy skeletal muscle which may provide a molecular basis for the inability of other laminin variants to compensate fully for the deficiency of merosin in some forms of muscular dystrophy.

Dystrophin-glycoprotein complex is monomeric and stabilizes actin filaments in vitro through a lateral association.

The native molecular weight of the dystrophin-glycoprotein complex and its effect on actin depolymerization and polymerization were examined. First, we determined that the native molecular weight of purified dystrophin-glycoprotein complex is only large enough (Mr 1,200,000) to contain one copy of each protein in the complex, including dystrophin. Using different approaches, we also demonstrated that dystrophin-glycoprotein complex significantly protected a fraction of actin filaments from disassembly, while individual recombinant actin binding fragments of dystrophin or calpain-digested dystrophin-glycoprotein complex had no effect on F-actin depolymerization. The protective effect of dystrophin-glycoprotein complex on F-actin depolymerization saturated at a dystrophin:actin molar ratio of 0.04, corresponding to 1 dystrophin/25 actin monomers, which is highly consistent with the 1:24 stoichiometry of dystrophin-glycoprotein complex binding to F-actin previously measured at equilibrium. However, dystrophin-glycoprotein complex did not bind G-actin or alter the kinetics or extent of actin polymerization. This excluded the possibility that dystrophin-glycoprotein complex inhibited actin depolymerization by capping the ends of actin filaments. It therefore appears that actin binding domains separated on the dystrophin molecule from each other by almost 1,200 amino acids act in concert to protect F-actin from depolymerization. Our data suggest that dystrophin stabilizes F-actin in vitro by binding alongside an actin filament and bridging actin monomers in a manner analogous to the actin side binding protein tropomyosin. It is noteworthy that we did not find any effect of skeletal muscle tropomyosin on dystrophin-glycoprotein complex binding to F-actin. This indicates that dystrophin-glycoprotein complex and tropomyosin may simultaneously bind the same actin filament and identifies another feature that distinguishes dystrophin from the other proteins in the actin-cross-linking superfamily.

Tissue-specific heterogeneity in alpha-dystroglycan sialoglycosylation. Skeletal muscle alpha-dystroglycan is a latent receptor for Vicia villosa agglutinin b4 masked by sialic acid modification.

Because the polypeptide core of alpha-dystroglycan is encoded by a single gene, the difference in apparent molecular mass between alpha-dystroglycans expressed in various tissues is presumably due to differential glycosylation. However, little is presently known about the tissue-specific differences in alpha-dystroglycan glycosylation and whether these modifications may confer functional variability to alpha-dystroglycan. We recently observed that laminin-1 binding to skeletal muscle alpha-dystroglycan was dramatically inhibited by heparin, whereas the binding of commercial merosin to skeletal muscle alpha-dystroglycan was only marginally inhibited (Pall, E. A., Bolton, K. M., and Ervasti, J. M. (1996) J. Biol. Chem. 3817-3821). In contrast to 156-kDa skeletal muscle alpha-dystroglycan, both laminin-1 and merosin binding to 120-kDa brain alpha-dystroglycan were sensitive to heparin. We have now examined the laminin binding properties of 140-kDa alpha-dystroglycan purified from cardiac muscle and observed that like skeletal muscle alpha-dystroglycan, heparin inhibited cardiac alpha-dystroglycan binding to laminin-1, but not to merosin. On the other hand, cardiac and brain alpha-dystroglycans could be distinguished from skeletal muscle alpha-dystroglycan by their reactivity with the terminal GalNAc-specific lectin Vicia villosa agglutinin. Interestingly, skeletal muscle alpha-dystroglycan became reactive with V. villosa agglutinin upon digestion with sialidase from Clostridium perfringens, Arthrobacter neurofaciens, or Streptococcus, but not Vibrio cholerae or Newcastle disease virus sialidase. While none of the sialidase treatments affected the laminin binding properties of alpha-dystroglycan, the sum of our results suggests that skeletal muscle alpha-dystroglycan contains a novel sialic acid residue linked alpha2-6 to GalNAc. These properties are also consistent with the cellular characteristics of a GalNAc-terminated glycoconjugate recently implicated in neuromuscular synaptogenesis. Thus, variations in alpha-dystroglycan sialoglycosylation may prove as useful markers to further elucidate the role of alpha-dystroglycan glycoforms in different tissues and perhaps within a single cell type.

A new model for the interaction of dystrophin with F-actin.

The F-actin binding and cross-linking properties of skeletal muscle dystrophin-glycoprotein complex were examined using high and low speed cosedimentation assays, microcapillary falling ball viscometry, and electron microscopy. Dystrophin-glycoprotein complex binding to F-actin saturated near 0.042 +/- 0.005 mol/ mol, which corresponds to one dystrophin per 24 actin monomers. Dystrophin-glycoprotein complex bound to F-actin with an average apparent Kd for dystrophin of 0.5 microM. These results demonstrate that native, full-length dystrophin in the glycoprotein complex binds F-actin with some properties similar to those measured for several members of the actin cross-linking super-family of proteins. However, we failed to observe dystrophin-glycoprotein complex-induced cross-linking of F-actin by three different methods, each positively controlled with alpha-actinin. Furthermore, high speed cosedimentation analysis of dystrophin-glycoprotein complex digested with calpain revealed a novel F-actin binding site located near the middle of the dystrophin rod domain. Recombinant dystrophin fragments corresponding to the novel actin binding site and the first 246 amino acids of dystrophin both bound F-actin but with significantly lower affinity and higher capacity than was observed with purified dystrophin-glycoprotein complex. Finally, dystrophin-glycoprotein complex was observed to significantly slow the depolymerization of F-actin, Suggesting that dystrophin may lie along side an actin filament through interaction with multiple actin monomers. These data suggest that although dystrophin is most closely related to the actin cross-linking superfamily based on sequence homology, dystrophin binds F-actin in a manner more analogous to actin side-binding proteins.

Nonnuclear DNA binding proteins in striated muscle.

The mechanism by which striated muscle internalizes plasmid DNA is unknown. A survey of nonnuclear membrane-associated DNA binding proteins from both skeletal and cardiac muscle revealed several sarcoplasmic reticulum restricted DNA binding species. 22P-DNA overlay and DNA-cellulose chromatography were used to identify membrane-associated DNA binding proteins that may mediate the uptake and expression of plasmid DNA by striated muscle. A total membrane vesicle fraction prepared from rabbit skeletal muscle contained 95-, 60-, and 28-kDa proteins that bound double-strand DNA specifically and with high affinity. The DNA binding proteins appear to originate from the sarcoplasmic reticulum because of their absence in purified sarcolemma vesicles and codistribution with several sarcoplasmic reticulum markers after subcellular fractionation. Several distinguishing biochemical features as well as cross-reactivity with triadin-specific antibodies indicated that the 95- and 60-kDa DNA binding proteins are triadin or proteolytic fragments of triadin, respectively. The role of these sarcoplasmic reticulum proteins in the transport of plasmid DNA is discussed.

Differential heparin inhibition of skeletal muscle alpha-dystroglycan binding to laminins.

The laminin binding properties of alpha-dystroglycan purified from rabbit skeletal muscle membranes were examined. In a solid phase microtiter assay, 125I-laminin (laminin-1) bound to purified alpha-dystroglycan in a specific and saturable manner with a half-maximal concentration of 8 nM. The binding of 125I- alpha-dystroglycan to native laminin and merosin (a mixture of laminin-2 and -4) was also compared using the solid phase assay. The absolute binding of 125I- alpha-dystroglycan to laminin (6955 +/- 250 cpm/well) was similar to that measured for merosin (7440 +/- 970 cpm/well). However, inclusion of 1 mg/ml heparin in the incubation medium inhibited 125I-alpha-dystroglycan binding to laminin by 84 +/- 4.3% but inhibited 125I-alpha-dystroglycan binding to merosin by only 17 +/- 5.2%. Similar results were obtained with heparan sulfate, while de-N-sulfated heparin, hyaluronic acid, and chondroitin sulfate had no differential effect. These results were confirmed by iodinated laminin and merosin overlay of electrophoretically separated and blotted dystrophin-glycoprotein complex. In contrast to the results obtained with skeletal muscle alpha-dystroglycan, both laminin and merosin binding to purified brain alpha-dystroglycan was significantly inhibited by heparin. Our data support the possibility that one or more heparan sulfate proteoglycans may specifically modulate the interaction of alpha-dystroglycan with different extracellular matrix proteins in skeletal muscle.

Alpha-dystroglycan deficiency correlates with elevated serum creatine kinase and decreased muscle contraction tension in golden retriever muscular dystrophy.

The dystrophin-glycoprotein complex was examined in dystrophin-deficient dogs with golden retriever muscular dystrophy (GRMD) using immunoblot and immunofluorescence analysis. The dystrophin-associated proteins were substantially reduced in muscle from dogs with GRMD. Interestingly, regression analysis revealed a strong correlation between the amount of alpha-dystroglycan and serum creatine kinase levels and the contraction tension measured for a given peroneus longus muscle.

Skeletal muscle junctional membrane protein content in pigs with different ryanodine receptor genotypes.

The content of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, transverse tubule dihydropyridine receptor (DHPR), and SR ryanodine receptor (RyR) was determined in muscle of pigs homozygous for the normal RyR allele and homozygous or heterozygous for the malignant hyperthermia-susceptible (MHS) RyR allele. Total muscle membranes isolated from 1-day-old pigs of the three different genotypes did not differ in the content of any of these proteins. However, at 28 days of age, crude membranes and total muscle homogenates from homozygous MHS pigs exhibited only 61-81% of the [3H]PN 200-110 or [3H]ryanodine binding of identical preparations isolated from normal pigs; these MHS membranes also contained only 50% of the normal content of each of the DHPR subunits. The crude membranes and muscle homogenates from heterozygous pigs were intermediate to both types of homozygotes in terms of [3H]PN 200-110 binding, [3H]ryanodine binding, and the content of the DHPR subunits. However, membrane preparations enriched in triadic junctional proteins isolated from 3- to 4-mo-old pigs of the three different genotypes did not differ in their [3H]PN 200-110 binding, [3H]ryanodine binding, or Ca(2+)-ATPase activities. We conclude that, although the stoichiometry of the RyR to DHPR is not altered, the presence of the MHS RyR allele during muscle development results in a decreased relative content of these two proteins. This is probably due to a lower junctional membrane content and may be an important ultrastructural consequence of the altered sarcoplasmic Ca2+ regulation in MHS muscle.