Comparison of transcutaneous tibial nerve stimulation (TTNS) protocols for women with refractory overactive bladder (OAB): A prospective randomised trial.

OBJECTIVES: Transcutaneous tibial nerve stimulation (TTNS) is a noninvasive method used in OAB treatment. Purpose of this study is to compare the effectiveness of the TTNS procedure applied once a week and three times a week in women diagnosed with wet type refractory OAB. METHODS: A total of 60 patients diagnosed with wet type OAB that was refractory to medical treatment were included in the study. Participants were equally and randomly divided into two groups: TTNS treatment was performed with a duration of 30 minutes for 12 weeks, once a week to Group I and three times a week to Group II. Pretreatment and posttreatment OAB-V8/ICIQ-SF scores and voiding frequencies recorded in the bladder diary were compared between groups. RESULTS: Four patients in Group 1 and eight in Group 2 left the study without completing the treatment. TTNS was performed in both groups for 12 weeks. There was a significant decrease in the voiding frequency, OAB-V8, ICIQ-SF scores in both group 1 and group 2 (P < .001). A significant decrease in the OAB-V8 score was observed in the 5th week in Group 1, and in the 3rd week in Group 2. Complete response was observed in 6 patients (23.1%) in Group 1 after 12 weeks of TTNS procedure. In Group 2, 10 patients (45.5%) had a complete response. After the 12-week TTNS procedure, no significant difference was observed between the groups in terms of treatment response. CONCLUSION: TTNS can be safely used before invasive treatments in resistant OAB. TTNS procedure three times a week seems more effective than performing it once a week. What's known TTNS is one of the effective alternative treatments in resistant OAB treatment. What's new As the number of sessions is increased in TTNS treatment, the success of the treatment can increase.

Urinary Titin N-Fragment Evaluation in a Randomized Controlled Trial of Beta-Hydroxy-Beta-Methylbutyrate for Acute Mild Trauma in Older Adults.

The effects of beta-hydroxy-beta-methylbutyrate (HMB) complex administration and the significance of titin, a biomarker of muscle injury, in elderly minor trauma patients in acute phase has not been established. In this single-center, randomized controlled study, trauma patients aged ≥ 70 years with an injury severity score < 16 were included. Titin values on days 1 and 3 were measured and the intervention group received HMB complex (2.4 g of HMB + 14 g of glutamine + 14 g of arginine) and the control group received glutamine complex (7.2 g of protein including 6 g of glutamine). The cross-sectional area of the rectus femoris (RFCSA) on ultrasound, grip strength, and the Barthel Index were assessed on the first day of rehabilitation and after 2 weeks. We analyzed 24 HMB and 25 control participants. Titin values on day 3 correlated with grip strength (r = -0.34, p = 0.03) and the Barthel Index (r = -0.39, p = 0.01) at follow-up. HMB complex supplementation had no effect on the RFCSA (2.41 vs. 2.45 cm2, p = 0.887), grip strength (13.3 vs. 13.1 kg, p = 0.946), or the Barthel Index (20.0 vs. 50.0, p = 0.404) at follow-up. Titin values might associate with subsequent physical function. Short-term HMB complex supplementation from acute phase did not ameliorate muscle injury.

Clinical efficacy of transcutaneous tibial nerve stimulation (TTNS) versus sham therapy (part I) and TTNS versus percutaneous tibial nerve stimulation (PTNS) (part II) on the short term in children with the idiopathic overactive bladder syndrome: protocol for part I of the twofold double-blinded randomized controlled TaPaS trial.

BACKGROUND: Transcutaneous tibial nerve stimulation (TTNS) and percutaneous tibial nerve stimulation (PTNS) are effective and safe therapies for overactive bladder (OAB) syndrome in adults. However, few randomized sham-controlled trials have been conducted in a pediatric population. To our knowledge, both therapies never have been compared in children. AIM: The aim of the complete study is twofold: (1) to assess the efficacy of TTNS therapy on bladder symptoms after 12 weeks of treatment in a pediatric population with idiopathic overactive bladder syndrome (iOAB) and/or nocturnal enuresis (part I) and (2) to assess the effect of TTNS compared to PTNS (part II). In this article, we aim to present the protocol of the first part of the TaPaS trial (TTNS, PTNS, sham therapy). METHODS: Part I of the TaPaS trial is set up as a single-center randomized-controlled trial. Children, aged from 5 to 12 years with iOAB and/or nocturnal enuresis, are assigned to two groups by computer-generated randomization: TTNS therapy (intervention) and sham therapy (control). The primary outcome is the percentage difference in average voided volume (AVV) between baseline and after 12 weeks of treatment. Secondary endpoints are the percentage difference in supervoid volumes, number of urinary incontinence episodes/24 h and in voiding frequency, the difference in parent reported outcomes between baseline and after 12 weeks of treatment, and the duration of clinical response. DISCUSSION: We hypothesize that TTNS is a non-inferior treatment for iOAB in children compared to PTNS therapy. Since literature is inconclusive about the efficacy of TTNS in a pediatric population, a sham-controlled RCT on TTNS will be conducted (part I). A protocol for a prospective randomized sham-controlled trial has been developed. Enrolment has started in November 2018. Study completion of part I is expected by August 2021. TRIAL REGISTRATION: ClinicalTrials.gov NCT04256876 . Retrospectively registered on February 5, 2020.

Autoantibodies in acquired myasthenia gravis: Clinical phenotype and immunological correlation.

BACKGROUND: Data on antibody profile in myasthenia gravis (MG) from India are limited. OBJECTIVES: To investigate antibody profile in patients with MG and their clinical correlates. PATIENTS AND METHODS: Patients of MG (n = 85, M:F::1.1:1, mean age: 39.29 ± 17.3 years, mean symptom duration: 72.94 ± 91.8 months) were evaluated for clinical features, MG foundation of America (MGFA) score, response to treatment, and outcome at last follow-up. Antibodies to acetylcholine receptor (AChR), muscle-specific kinase (MUSK), titin and ryanodine receptor (RYR) were analysed using ELISA. RESULTS: Based on the regional distribution of weakness, the cohort could be categorized as: generalized: 60, ocular: 16 and oculo-bulbar: 9. Sixty patients were followed up for a mean duration of 26.74 ± 13.8 months. Outcome at last follow-up was as follows: remission-22, no remission-33 and dead-5. AChR and MUSK antibodies were detected in 58 and 8 patients, respectively. Frequency of generalized MG, worse MGFA score during the disease course and thymomatous histology significantly correlated with presence of AChR-antibodies, though outcome at last follow-up was comparable between AChR-antibody positive and negative groups. Patients with MUSK antibodies had oculo-bulbar or generalized MG and frequent respiratory crisis, but majority improved or remitted with treatment. Titin antibodies were detected in 31.8% and RYR antibodies in 32.9%. Their presence did not correlate with age at onset of MG, severity or presence of thymoma. CONCLUSION: This report highlights the spectrum of antibodies in MG in an Indian cohort. AChR-antibody positivity correlated with clinical severity. Outcome was good in majority of MUSK antibody-positive MG. The role of other antibodies, complementary vs epiphenomenon, remains open.

Effects of dietary amino acid supplementation on measures of whole-body and muscle protein metabolism in aged horses.

The objective of this study was to examine markers of whole-body and muscle protein metabolism in aged horses fed a diet typical for North American aged horses, supplemented with amino acids. In a replicated Latin square design, six aged horses (20 ± 1.1 years) were studied while receiving each of three isocaloric, isonitrogenous diets, a control treatment concentrate (CON; 100 mg/kg-1 BW day-1 lysine, 84 mg kg-1  day-1 threonine, 51 mg kg-1  day-1 methionine), LYS/THR (134 mg kg-1 BW day-1 lysine, 110 mg kg-1 BW day-1 threonine, 52 mg kg-1 BW day-1 methionine) and LYS/THR/MET (132 mg kg-1 BW day-1 lysine, 112 mg kg-1 BW day-1 threonine, 62 mg kg-1 BW day-1 methionine). In each 15-days period, urine and faeces were collected for assessment of nitrogen balance. Blood samples were collected before and after feeding for analysis of plasma urea nitrogen (PUN), glucose, insulin and plasma amino acid concentrations. Skeletal muscle samples were collected for measurement of proteins associated with muscle protein synthesis and degradation, and horses underwent stable isotope infusion procedures for comparison of differences in whole-body rates of protein synthesis and degradation. There was no effect of treatment on relative abundance of proteins involved in protein synthesis, nitrogen retention or phenylalanine kinetics. PUN concentrations tended to be higher for LYS/THR (p = 0.054) and were higher for LYS/THR/MET (p = 0.0056) than for CON. Atrogin-1 abundance tended to be higher in the post-absorptive state for the CON treatment (p = 0.07), indicating that amino acid supplementation resulted in less muscle protein degradation when horses were in the post-absorptive state. However, lack of differences in nitrogen retention and phenylalanine kinetics indicated that whole-body protein metabolism was not improved, and higher PUN concentrations in the supplemented diets suggest that the supplemented amino acids may have been catabolized. Amino acid availability was not limiting protein synthesis in the sedentary aged horses in this study when fed the CON diet.

Passive mechanical properties and related proteins change with botulinum neurotoxin A injection of normal skeletal muscle.

The effects of botulinum neurotoxin A on the passive mechanical properties of skeletal muscle have not been investigated, but may have significant impact in the treatment of neuromuscular disorders including spasticity. Single fiber and fiber bundle passive mechanical testing was performed on rat muscles treated with botulinum neurotoxin A. Myosin heavy chain and titin composition of single fibers was determined by gel electrophoresis. Muscle collagen content was determined using a hydroxyproline assay. Neurotoxin-treated single fiber passive elastic modulus was reduced compared to control fibers (53.00 kPa vs. 63.43 kPa). Fiber stiffness and slack sarcomere length were also reduced compared to control fibers and myosin heavy chain composition shifted from faster to slower isoforms. Average titin molecular weight increased 1.77% after treatment. Fiber bundle passive elastic modulus increased following treatment (168.83 kPa vs. 75.14 kPa). Bundle stiffness also increased while collagen content per mass of muscle tissue increased 38%. Injection of botulinum neurotoxin A produces an effect on the passive mechanical properties of normal muscle that is opposite to the changes observed in spastic muscles.

Increased myocardial stiffness with maintenance of length-dependent calcium activation by female sex hormones in diabetic rats.

A decrease in peak early diastolic filling velocity in postmenopausal women implies a sex hormone-related diastolic dysfunction. The regulatory effect of female sex hormones on cardiac distensibility therefore was evaluated in ovariectomized rats by determining the sarcomere length-passive tension relationship of ventricular skinned fiber preparations. Diabetes also was induced in the rat to assess the protective significance of female sex hormones on diastolic function. While ovariectomy had no effect on myocardial stiffness, collagen content, or titin ratio, a significant increase in myocardial stiffness was observed in diabetic rat only when female sex hormones were intact. The increased stiffness in diabetic-sham rats was accompanied by an elevated collagen content resulting from increases in the levels of procollagen and Smad2. Surprisingly, the increased myocardial stiffness in diabetic-sham rats was accompanied by a shift toward a more compliant N2BA of cardiac titin isoforms. The pCa-active tension relationship was analyzed at fixed sarcomere lengths of 2.0 and 2.3 µm to determine the magnitude of changes in myofilament Ca(2+) sensitivity between the two sarcomere lengths. Interestingly, high expression of N2BA titin was associated with a suppressed magnitude of changes in myofilament Ca(2+) sensitivity only in the diabetic-ovariectomized condition. Estrogen supplementation in diabetic-ovariectomized rats partially increased myocardial stiffness but completely reversed the change in myofilament Ca(2+) sensitivity. These results indicate a restrictive adaptation of myocardium governed by female sex hormones to maintain myofilament activity in compensation to the pathophysiological induction of cardiac dilatation by the diabetic condition.

The effect of gypenosides on cardiac function and expression of cytoskeletal genes of myocardium in diabetic cardiomyopathy rats.

The relationship between changes of cardiac function and the gene expressions of two major myocardial skeleton proteins, titin and nebulin, and the effect of gypenosides on these gene expressions in diabetic cardiomyopathy rat were explored in the present study. Forty Sprague-Dawley rats were randomly divided into three groups: control group, diabetic cardiomyopathy group and gypenosides-treated diabetic cardiomyopathy group. The diabetic cardiomyopathy was induced in rats by injecting streptozotocin (STZ, 55 mg/kg) intraperitoneally. Seven weeks after the rats suffered from diabetes, the rats were treated with gypenosides 100 mg/kg per day orally for six weeks in gypenosides-treated group. In the meanwhile, the pure water was given to diabetic cardiomyopathy and the control groups. Subsequently, the cardiac functions, including left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), +/- dP/dt(max) and t-dP/d(max)t, as well as the mRNA content and proteins of titin and nebulin in myocardium were determined. The results indicated that (1) the diabetic cardiomyopathy rats had decreased LVSP and +/- dP/dt(max), increased LVEDP, and prolonged t-dP/dt(max) than normal rats; (2) LVSP and +/- dP/dt(max) in diabetic cardiomyopathy rats treated with gypenosides were significantly higher and LVEDP and t-dP/dt(max) were significantly lower than those without giving gypenosides; (3) the mRNA contents and proteins of titin and nebulin in diabetic cardiomyopathy rats were remarkably lower than those in the control rats and gypenosides had no effect on mRNA and protein expression levels of titin and nebulin in diabetic cardiomyopathy rats. We conclude that (1) the cardiac function as well as the mRNA expressions of titin and nebulin decreased in diabetic cardiomyopathy rats; (2) gypenosides secure cardiac muscles and their function from diabetic impairment and these beneficial effects of gypenosides are not by changing the expressions of titin and nebulin.

Effects of fatiguing jumping exercise on mRNA expression of titin-complex proteins and calpains.

Eccentric exercise induced by electrostimulation increases mRNA expression of titin-complex proteins in rodent skeletal muscle. In this study, mRNA expression of titin, muscle LIM protein (MLP), cardiac ankyrin repeat protein (CARP), ankyrin repeat domain protein 2 (Ankrd2), diabetes-related ankyrin repeat protein (DARP), and calcium-activated proteinases, calpains, were investigated in human skeletal muscle after fatiguing jumping exercise. Fatiguing jumping exercise did not change mRNA expression of titin, DARP, calpain 1, or calpain 3. MLP, Ankrd2 and calpain 2 mRNA levels were increased 2 days postexercise. CARP mRNA level was already elevated 30 min and remained elevated 2 days postexercise. Increased mRNA expression of MLP, CARP, and Ankrd2, observed for the first time in human skeletal muscle, may be part of the signaling activated by physical exercise. The rapid increase in the level of CARP mRNA nominates CARP as one of the first genes to respond to exercise. The increase in the mRNA level of calpain 2 suggests its involvement in myofiber remodeling after strenuous jumping exercise.

Differential actin binding along the PEVK domain of skeletal muscle titin.

Parts of the PEVK (Pro-Glu-Val-Lys) domain of the skeletal muscle isoform of the giant intrasarcomeric protein titin have been shown to bind F-actin. However, the mechanisms and physiological function of this are poorly understood. To test for actin binding along PEVK, we expressed contiguous N-terminal (PEVKI), middle (PEVKII), and C-terminal (PEVKIII) PEVK segments of the human soleus muscle isoform. We found a differential actin binding along PEVK in solid-state binding, cross-linking and in vitro motility assays. The order of apparent affinity is PEVKII>PEVKI>PEVKIII. To explore which sequence motifs convey the actin-binding property, we cloned and expressed PEVK fragments with different motif structure: PPAK, polyE-rich and pure polyE fragments. The polyE-containing fragments had a stronger apparent actin binding, suggesting that a local preponderance of polyE motifs conveys an enhanced local actin-binding property to PEVK. The actin binding of PEVK may serve as a viscous bumper mechanism that limits the velocity of unloaded muscle shortening towards short sarcomere lengths. Variations in the motif structure of PEVK might be a method of regulating the magnitude of the viscous drag.

Protein kinase D is a novel mediator of cardiac troponin I phosphorylation and regulates myofilament function.

Protein kinase D (PKD) is a serine kinase whose myocardial substrates are unknown. Yeast 2-hybrid screening of a human cardiac library, using the PKD catalytic domain as bait, identified cardiac troponin I (cTnI), myosin-binding protein C (cMyBP-C), and telethonin as PKD-interacting proteins. In vitro phosphorylation assays revealed PKD-mediated phosphorylation of cTnI, cMyBP-C, and telethonin, as well as myomesin. Peptide mass fingerprint analysis of cTnI by liquid chromatography-coupled mass spectrometry indicated PKD-mediated phosphorylation of a peptide containing Ser22 and Ser23, the protein kinase A (PKA) targets. Ser22 and Ser23 were replaced by Ala, either singly (Ser22Ala or Ser23Ala) or jointly (Ser22/23Ala), and the troponin complex reconstituted in vitro, using wild-type or mutated cTnI together with wild-type cardiac troponin C and troponin T. PKD-mediated cTnI phosphorylation was reduced in complexes containing Ser22Ala or Ser23Ala cTnI and completely abolished in the complex containing Ser22/23Ala cTnI, indicating that Ser22 and Ser23 are both targeted by PKD. Furthermore, troponin complex containing wild-type cTnI was phosphorylated with similar kinetics and stoichiometry (approximately 2 mol phosphate/mol cTnI) by both PKD and PKA. To determine the functional impact of PKD-mediated phosphorylation, Ca2+ sensitivity of tension development was studied in a rat skinned ventricular myocyte preparation. PKD-mediated phosphorylation did not affect maximal tension but produced a significant rightward shift of the tension-pCa relationship, indicating reduced myofilament Ca2+ sensitivity. At submaximal Ca2+ activation, PKD-mediated phosphorylation also accelerated isometric crossbridge cycling kinetics. Our data suggest that PKD is a novel mediator of cTnI phosphorylation at the PKA sites and may contribute to the regulation of myofilament function.

Isolation and characterization of 190K protein from aorta smooth muscle.

Molecular assemblies of actin and myosin for the contractility of smooth muscle are quite different from those of striated muscle. Another striking difference is that vascular smooth muscle has a potential to transform to migratory synthetic cell type. At this point of view, smooth muscle cell has properties similar to those of non-muscle. In fact, myosin Ic, a single headed unconventional myosin, was identified in aorta smooth muscle. During the studies on myosin Ic, we have found another calmodulin related 190kDa protein. This protein binds to calmodulin irrespective on calcium ion and to F-actin in an ATP independent manner. Furthermore, the F-actin binding stoichiometry diminished to half upon the addition of exogenous calmodulin. Partial amino acid sequence indicated a high homology to those of GRD (GTPase Related Domain) of human brain IQGAP1. Western blot analysis using anti-human IQGAP1 antibody also indicated a strong cross-reactivity with the protein. We have tested the protein with respect to the characteristic F-actin gelation by IQGAP1. In the presence of cdc42 and GTPgammaS, 190kDa protein could cause a high viscosity of F-actin. These data indicate a close similarity to human brain IQGAP1. The presence of IQGAP1 in aorta smooth muscle suggests contributions for cellular processes such as actin reorganization during contraction-relaxation cycle, association of cytoskeletal structure to cell membrane, organelle movement.

Rabconnectin-3, a novel protein that binds both GDP/GTP exchange protein and GTPase-activating protein for Rab3 small G protein family.

Rab3A, a member of the Rab3 small G protein family, regulates Ca(2+)-dependent exocytosis of neurotransmitter. The cyclical activation and inactivation of Rab3A are essential for the Rab3A action in exocytosis. GDP-Rab3A is activated to GTP-Rab3A by Rab3 GDP/GTP exchange protein (Rab3 GEP), and GTP-Rab3A is inactivated to GDP-Rab3A by Rab3 GTPase-activating protein (Rab3 GAP). It remains unknown how or in which step of the multiple exocytosis steps these regulators are activated and inactivated. We isolated here a novel protein that was co-immunoprecipitated with Rab3 GEP and GAP by their respective antibodies from the crude synaptic vesicle fraction of rat brain. The protein, named rabconnectin-3, bound both Rab3 GEP and GAP. The cDNA of rabconnectin-3 was cloned from a human cDNA library and its primary structure was determined. Human rabconnectin-3 consisted of 3,036 amino acids and showed a calculated M(r) of 339,753. It had 12 WD domains. Tissue and subcellular distribution analyses in rat indicated that rabconnectin-3 was abundantly expressed in the brain where it was enriched in the synaptic vesicle fraction. Immunofluorescence and immunoelectron microscopy revealed that rabconnectin-3 was concentrated on synaptic vesicles at synapses. These results indicate that rabconnectin-3 serves as a scaffold molecule for both Rab3 GEP and GAP on synaptic vesicles.

Modular motif, structural folds and affinity profiles of the PEVK segment of human fetal skeletal muscle titin.

The extension of the PEVK segment of the giant elastic protein titin is a key event in the elastic response of striated muscle to passive stretch. PEVK behaves mechanically as an entropic spring and is thought to be a random coil. cDNA sequencing of human fetal skeletal PEVK reveals a modular motif with tandem repeats of modules averaging 28 residues and with superrepeats of seven modules. Conformational studies of bacterially expressed 53-kDa fragment (TP1) by circular dichroism suggest that this soluble protein contains substantial polyproline II (PPII) type left-handed helices. Urea and thermal titrations cause gradual and reversible decrease in PPII content. The absence of sharp melting in urea and thermal titrations suggests that there is no long range cooperativity among the PPII helices. Studies with solid phase and surface plasmon resonance assays indicate that TP1 interacts with actin and some but not all cloned nebulin fragments with high affinity. Interestingly, Ca(2+)/calmodulin and Ca(2+)/S100 abolish nebulin/PEVK interaction. We suggest that in aqueous solution, PEVK is an open and flexible chain of relatively stable structural folds of the polyproline II type. PEVK region of titin may be involved in interfilament association with thin filaments in a calcium/calmodulin-sensitive manner. This adhesion may modulate titin extensibility and elasticity.

The interaction of titin and alpha-actinin is controlled by a phospholipid-regulated intramolecular pseudoligand mechanism.

The assembly of stable cytoskeletal structures from dynamically recycled molecules requires developmental and spatial regulation of protein interactions. In muscle, titin acts as a molecular ruler organizing the actin cytoskeleton via interactions with many sarcomeric proteins, including the crosslinking protein alpha-actinin. An interaction between the C-terminal domain of alpha-actinin and titin Z-repeat motifs targets alpha-actinin to the Z-disk. Here we investigate the cellular regulation of this interaction. alpha-actinin is a rod shaped head-to-tail homodimer. In contrast to C-terminal fragments, full-length alpha-actinin does not bind Z-repeats. We identify a 30-residue Z-repeat homologous sequence between the actin-binding and rod regions of alpha-actinin that binds the C-terminal domain with nanomolar affinity. Thus, Z-repeat binding is prevented by this 'pseudoligand' interaction between the subunits of the alpha-actinin dimer. This autoinhibition is relieved upon binding of the Z-disk lipid phosphatidylinositol-bisphosphate to the actin-binding domain. We suggest that this novel mechanism is relevant to control the site-specific interactions of alpha-actinin during sarcomere assembly and turnover. The intramolecular contacts defined here also constrain a structural model for intrasterical regulation of all alpha-actinin isoforms.

Modulation of sarcomere organization during embryonic stem cell-derived cardiomyocyte differentiation.

Myofibrillogenesis - sarcomeres - mouse embryonic stem cells - cardiomyocytes - beta1 integrin Mouse embryonic stem (ES) cells, when cultivated as embryoid bodies, differentiate in vitro into cardiomyocytes of ventricle-, atrium- and pacemaker-like cell types characterized by developmentally controlled expression of cardiac-specific genes, structural proteins and ion channels. Using this model system, we show here, (I) that during cardiac myofibrillogenesis sarcomeric proteins are organized in a developmentally regulated manner following the order: titin (Z-disk), alpha-actinin, myomesin, titin (M-band), myosin heavy chain, alpha-actin, cardiac troponin T and M-protein, recapitulating the sarcomeric organization in the chicken embryonal heart in vivo. Our data support the view that the formation of I-Z-I complexes is developmentally delayed with respect to A-band assembly. We show (2) that the process of cardiogenic differentiation in vitro is influenced by medium components: Using a culture medium supplemented with glucose, amino acids, vitamins and selenium ions, we were able to increase the efficiency of cardiac differentiation of wild-type, as well as of beta1 integrin-deficient (beta1-/-) ES cells, and to improve the degree of organization of sarcomeric structures in wild-type and in beta1-/- cardiac cells. The data demonstrate the plasticity of cardiogenesis during the differentiation of wild-type and of genetically modified ES cells.

Muscle-specific calpain, p94, interacts with the extreme C-terminal region of connectin, a unique region flanked by two immunoglobulin C2 motifs.

Using the yeast two-hybrid system, we have recently reported that skeletal muscle-specific calpain, p94, binds specifically to connectin (or titin), a gigantic muscle elastic protein. Connectin has at least two binding sites for p94; one is at the N2-line region and the other is at the extreme C-terminus. In order to analyze the interaction between p94 and the C-terminus of connectin, we examined the C-terminal sequence of human skeletal muscle connectin. The sequence was essentially identical to that of heart muscle reported by Labeit and Kolmerer (1995, Science 270, 293-296), and the minimal binding site for p94 contained two IgC2 motifs and the intervening sequence called "M-is7." The exon encoding M-is7 is reported to be alternatively spliced depending on muscle tissues, resulting in the existence of both types of connectin with and without M-is7. However, the C-terminal region of connectin bound to p94 through M-is7. Our results suggest that the interaction between p94 and the C-terminus of skeletal muscle-type connectin is involved in tissue-specific myofibriogenesis.