Developing a Cell-Microcarrier Tissue-Engineered Product for Muscle Repair Using a Bioreactor System

Fecal incontinence, although not life-threatening, has a high impact on the economy and patient quality of life. So far, available treatments are based on both surgical and nonsurgical approaches. These can range from changes in diet, to bowel training, or sacral nerve stimulation, but none of which provides a long-term solution. New regenerative medicine-based therapies are emerging, which aim at regenerating the sphincter muscle and restoring continence. Usually, these consist of the administration of a suspension of expanded skeletal-derived muscle cells (SkMDCs) to the damaged site. However, this strategy often results in a reduced cell viability due to the need for cell harvesting from the expansion platform, as well as the non-native use of a cell suspension to deliver the anchorage-dependent cells. In this study, we propose the proof-of-concept for the bioprocessing of a new cell delivery method for the treatment of fecal incontinence, obtained by a scalable two-step process. First, patient-isolated SkMDCs were expanded using planar static culture systems. Second, by using a single-use PBS-MINI Vertical-Wheel® bioreactor, the expanded SkMDCs were combined with biocompatible and biodegradable (i.e., directly implantable) poly(lactic-co-glycolic acid) microcarriers prepared by thermally induced phase separation. This process allowed for up to 80% efficiency of SkMDCs to attach to the microcarriers. Importantly, SkMDCs were viable during all the process and maintained their myogenic features (e.g., expression of the CD56 marker) after adhesion and culture on the microcarriers. When SkMDC-containing microcarriers were placed on a culture dish, cells were able to migrate from the microcarriers onto the culture surface and differentiate into multinucleated myotubes, which highlights their potential to regenerate the damaged sphincter muscle after administration into the patient. Overall, this study proposes an innovative method to attach SkMDCs to biodegradable microcarriers, which can provide a new treatment for fecal incontinence.

Potency Assay Development: A Keystone for Clinical Use

Potency can be described as the quantitative measure of biological activity, that is, the ability of an Advanced Therapy Medicinal Product (ATMP) to elicit the intended effect necessary for clinical efficacy. Potency testing is part of the quality control strategy necessary for batch release and is required for market approval application of an ATMP. Thus, it is crucial to develop a reliable and accurate potency assay. As a prerequisite for potency assay development, it is essential to define the mode of action of the product and thereby also the relevant biological activity that should be measured. The establishment of a potency assay should be initiated already during early product development followed by its progressive implementation into an ATMP's manufacturing, quality control and release process. Potency testing is indispensable for clinical use with a wide range of applications. A potency assay is a valuable tool to determine the product's stability, detect the impact of changes in the manufacturing process on the product, demonstrate quality and manufacturing consistency from batch to batch, estimate clinical efficacy and define the effective dose. This chapter describes the requirements and challenges to be considered for potency assay development and the importance of a well-established potency assay for clinical use.

Skeletal muscle-derived cell implantation for the treatment of sphincter-related faecal incontinence

Background

In an earlier pilot study with 10 women, we investigated a new approach for therapy of faecal incontinence (FI) due to obstetric trauma, involving ultrasound-guided injection of autologous skeletal muscle-derived cells (SMDC) into the external anal sphincter (EAS), and observed significant improvement. In the current study, we tested this therapeutic approach in an extended patient group: male and female patients suffering from FI due to EAS damage and/or atrophy. Furthermore, feasibility of lower cell counts and cryo-preserved SMDC was assessed.

Methods

In this single-centre, explorative, baseline-controlled clinical trial, each patient (n = 39; mean age 60.6 ± 13.81 years) received 79.4 ± 22.5 × 10⁶ cryo-preserved autologous SMDC. Changes in FI parameters, Fecal Incontinence Quality of Life (FIQL), anorectal manometry and safety from baseline to 1, 6 and 12 months post implantation were evaluated.

Results

SMDC used in this trial contained a high percentage of myogenic-expressing (CD56⁺) and muscle stem cell marker-expressing (Pax7⁺, Myf5⁺) cells. Intervention was well tolerated without any serious adverse events. After 12 months, the number of weekly incontinence episodes (WIE, primary variable), FIQL and patient condition had improved significantly. In 80.6% of males and 78.4% of females, the WIE frequency decreased by at least 50%; Wexner scores and severity of FI complaints decreased significantly, independent of gender and cause of FI.

Conclusions

Injection of SMDCs into the EAS effectively improved sphincter-related FI due to EAS damage and/or atrophy in males and females. When confirmed in a larger, placebo-controlled trial, this minimal invasive procedure has the potential to become first-line therapy for FI.

Trial registration

EU Clinical Trials Register, EudraCT 2010-023826-19 (Date of registration: 08.11.2010).

Development of an in vitro potency assay for human skeletal muscle derived cells

BACKGROUND

Potency is a quantitative measure of the desired biological function of an advanced therapy medicinal product (ATMP) and is a prerequisite for market approval application (MAA). To assess the potency of human skeletal muscle-derived cells (SMDCs), which are currently investigated in clinical trials for the regeneration of skeletal muscle defects, we evaluated acetylcholinesterase (AChE), which is expressed in skeletal muscle and nervous tissue of all mammals.

METHODS

CD56+ SMDCs were separated from CD56- SMDCs by magnetic activated cell sorting (MACS) and both differentiated in skeletal muscle differentiation medium. AChE activity of in vitro differentiated SMDCs was correlated with CD56 expression, fusion index, cell number, cell doubling numbers, differentiation markers and compared to the clinical efficacy in patients treated with SMDCs against fecal incontinence.

RESULTS

CD56- SMDCs did not form multinucleated myotubes and remained low in AChE activity during differentiation. CD56+ SMDCs generated myotubes and increased in AChE activity during differentiation. AChE activity was found to accurately reflect the number of CD56+ SMDCs in culture, their fusion competence, and cell doubling number. In patients with fecal incontinence responding to SMDCs treatment, the improvement of clinical symptoms was positively linked with the AChE activity of the SMDCs injected.

DISCUSSION

AChE activity was found to truly reflect the in vitro differentiation status of SMDCs and to be superior to the mere use of surface markers as it reflects not only the number of myogenic SMDCs in culture but also their fusion competence and population doubling number, thus combining cell quality and quantification of the expected mode of action (MoA) of SMDCs. Moreover, the successful in vitro validation of the assay proves its suitability for routine use. Most convincingly, our results demonstrate a link between clinical efficacy and the AChE activity of the SMDCs preparations used for the treatment of fecal incontinence. Thus, we recommend using AChE activity of in vitro differentiated SMDCs as a potency measure in end stage (phase III) clinical trials using SMDCs for skeletal muscle regeneration and subsequent market approval application (MAA).

Functional and Histological Changes after Myoblast Injections in the Porcine Rhabdosphincter

OBJECTIVE

Transurethral ultrasound-guided injection of autologous myoblasts has recently been shown to cure urinary stress incontinence. In the present study, the dose-dependent changes in maximal urethral closure pressures after application of myoblasts were investigated in a porcine animal model.

METHODS

Myoblast cultures were grown from a porcine muscle biopsy. The biopsy was enzymatically dissociated by using a modified cell dispersion technique. Single myoblasts in suspension were manually collected with a micropipette under microscopic control. Next a clonal myoblast culture was prepared. Before the cells were applied, fluorescence labelling (PKH) was used to assess integration of the injected myoblasts into the rhabdosphincter. With the help of a transurethral ultrasound probe (23 F, 11 MHz) and a special injection system, the myoblasts were injected into the rhabdosphincter of five pigs under direct sonographic control. Into two different areas of the rhabdosphincter, increasing different cell counts were injected (total volume 1.5 ml). At each area, 10 depots of 150 microl volume were injected all along the rhabdosphincter. The following cell counts were used: 1.5 x 10(6), 2.1 x 10(6), 4.2 x 10(6) (low range) 5.69 x 10(6), 8.1 x 10(6), 1.13 x 10(7), 1.6 x 10(7) (mid range) 2.26 x 10(7), 4.4 x 10(7), and 7.8 x 10(7) (high range). To avoid possible cell rejection, we immunosuppressed the pigs with daily cortisone (1g Solu Dacortin) because allogenic myoblasts were used. Urethral pressure profiles (UPPs) were measured before and 3 wk postoperatively before the pigs were put to sleep. The lower urinary tract was removed in all pigs for histological analysis.

RESULTS

Histological examination of the specimens revealed that the injected cells had survived at the injection site and had formed new myofibres. Overall the UPP curves revealed dose-dependent changes. Statistically significant increased pressure values of up to more than 300% could be observed in all cases in which higher concentrations of cells had been applied. Increases were also noted in mid range concentrations although not to such a high extent (approximately 150%). Pressure values had even diminished (approximately 50%) after injecting the three lowest concentrations (1.5 x 10(6), 2.1 x 10(6), 4.2 x 10(6)).

CONCLUSIONS

The present results show that the effects after application of myoblasts into the rhabdosphincter are dose-dependent.

Autologous myoblasts and fibroblasts for female stress incontinence: a 1-year follow-up in 123 patients

OBJECTIVE

To assess the efficacy and safety of the application of autologous myoblasts and fibroblasts for treating female stress urinary incontinence (SUI) after a follow-up of >/=1 year.

PATIENTS AND METHODS

In all, 123 women with SUI (aged 36-84 years) were treated with transurethral ultrasonography-guided injections with autologous myoblasts and fibroblasts obtained from skeletal muscle biopsies. The fibroblasts were suspended in a small amount of collagen as carrier material and injected into the urethral submucosa, while the myoblasts were implanted into the rhabdosphincter. All patients were evaluated before and 12 months after the injection using the Incontinence and Quality of Life Instrument (I-QOL) scores, urodynamic variables, and morphology and function of the urethra and rhabdosphincter.

RESULTS

At 1 year after implanting the cells, 94 of the 119 women (79%) were completely continent, 16 (13%) had a substantial improvement and nine (8%) a slight improvement. Four patients were lost to follow-up. The incontinence and I-QOL scores, and the thickness, contractility and electromyographic activity of the rhabdosphincter were significantly improved after treatment.

CONCLUSIONS

These results show the efficacy and safety of transferring autologous myoblasts and fibroblasts in the treatment of female SUI, after a follow-up of 1 year.

Transurethral ultrasonography-guided injection of adult autologous stem cells versus transurethral endoscopic injection of collagen in treatment of urinary incontinence

In the last years preclinical studies have paved the way for the use of adult muscle derived stem cells for reconstruction of the lower urinary tract. Between September 2002 and October 2004, 42 women and 21 men suffering from urinary stress incontinence (age 36-84 years) were recruited and subsequently treated with transurethral ultrasonography-guided injections of autologous myoblasts and fibroblasts obtained from skeletal muscle biopsies. The fibroblasts were injected into the urethral submucosa, while the myoblasts were implanted into the rhabdosphincter. In parallel, 7 men and 21 women (age 39-83 years) also diagnosed with urinary stress incontinence were treated with standard transurethral endoscopic injections of collagen. Patients were randomly assigned to both groups. After a follow-up of 12 months incontinence was cured in 39 women and 11 men after injection of autologous myoblasts and fibroblasts. Mean quality of life score (51.38 preoperatively, 104.06 postoperatively), thickness of urethra and rhabdosphincter (2.103 mm preoperatively, 3.303 mm postoperatively) as well as contractility of the rhabdosphincter (0.56 mm preoperatively, 1.462 mm postoperatively) were improved postoperatively. Only in two patients treated with injections of collagen incontinence was cured. The present clinical results demonstrate that, in contrast to injections of collagen, urinary incontinence can be treated effectively with ultrasonography-guided injections of autologous myo- and fibroblasts.

Adult stem cell therapy of female stress urinary incontinence

OBJECTIVES

To investigate the efficacy of transurethral ultrasound (TUUS)-guided injections of autologous myoblasts and fibroblasts in women with incontinence.

METHODS

Between January and June 2005, 20 female patients suffering from stress urinary incontinence (SUI) were included. Skeletal muscle biopsies were taken from the left arm to obtain cultures from autologous fibroblasts and myoblasts. By TUUS guidance the fibroblasts were injected into the urethral submucosa and the myoblasts were injected into the rhabdosphincter. A defined incontinence score, quality-of-life score and urodynamic, electromyographic, and laboratory parameters, as well as morphology and function of urethra and rhabdosphincter were evaluated before and up to 2 yr after therapy.

RESULTS

Eighteen of 20 patients were cured 1 yr after injection of autologous stem cells and in 2 patients SUI was improved. Two years after therapy 16 of the 18 patients presented as cured, 2 others were improved, and 2 were lost to follow-up. Incontinence and quality-of-life scores were significantly improved postoperatively. The thickness of urethra and rhabdosphincter as well as activity and contractility of the rhabdosphincter were also statistically significantly increased after therapy.

CONCLUSIONS

Clinical results demonstrate that SUI can be treated effectively with autologous stem cells. The present data support the conclusion that this therapeutic concept represents an elegant and minimally invasive treatment modality to treat SUI.

Autologous myoblasts and fibroblasts versus collagen for treatment of stress urinary incontinence in women: a randomised controlled trial

BACKGROUND

Preclinical studies have suggested that transurethral injections of autologous myoblasts can aid in regeneration of the rhabdosphincter, and fibroblasts in reconstruction of the urethral submucosa. We aimed to compare the effectiveness and tolerability of ultrasonography-guided injections of autologous cells with those of endoscopic injections of collagen for stress incontinence.

METHODS

Between 2002 and 2004, we recruited 63 eligible women with urinary stress incontinence. 42 of these women were randomly assigned to receive transurethral ultrasonography-guided injections of autologous myoblasts and fibroblasts, and 21 to receive conventional endoscopic injections of collagen. The first primary outcome measure was an incontinence score (range 0-6) based on a 24-hour voiding diary, a 24-hour pad test, and a patient questionnaire. The other primary outcome measures were contractility of the rhabdosphincter and thickness of both the urethra and rhabdosphincter. Analysis was by intention to treat. This trial is registered with Controlled-Trials.com, number CCT-NAPN-16630.

FINDINGS

At 12-months' follow-up, 38 of the 42 women injected with autologous cells were completely continent, compared with two of the 21 patients given conventional treatment with collagen. The median incontinence score decreased from a baseline of 6.0 (IQR 6.0-6.0; where 6 represents complete incontinence), to 0 (0-0) for patients treated with autologous cells, and 6.0 (3.5-6.0) for patients treated with collagen (p<0.0001). Ultrasonographic measurements showed that the mean thickness of the rhabdosphincter increased from a baseline of 2.13 mm (SD 0.39) for all patients to 3.38 mm (0.26) for patients treated with autologous cells and 2.32 mm (0.44) for patients treated with collagen (p<0.0001). Contractility of the rhabdosphincter increased from a baseline of 0.58 mm (SD 0.32) to 1.56 mm (0.28) for patients treated with autologous cells and 0.67 mm (0.51) for controls (p<0.0001). The change in the thickness of the urethra after treatment was not significantly different between treatment groups. No adverse effects were recorded in any of the 63 patients.

INTERPRETATION

Long-term postoperative results and data from multicentre trials with larger numbers of patients are needed to assess whether injection of autologous cells into the rhabdosphincter and the urethra could become a standard treatment for urinary incontinence.

Combined transplantation of skeletal myoblasts and angiopoietic progenitor cells reduces infarct size and apoptosis and improves cardiac function in chronic ischemic heart failure

OBJECTIVES

Cellular cardiomyoplasty using skeletal myoblasts or angiopoietic progenitor cells offers a promising approach for the treatment of ischemic heart failure. Although several studies have shown encouraging results in acute myocardial infarction, the efficacy of cell therapy using skeletal myoblasts and angiopoietic progenitor cells in chronic ischemic heart disease remains undetermined.

METHODS

Ischemic heart failure was induced by left anterior descending coronary artery ligation in nude rats: (1) Culture medium, (2) homologous skeletal myoblasts (SM), (3) human AC-133+ cells (SC), and (4) both skeletal myoblasts and AC-133+ cells (Comb) were injected in the infarct (SM) and peri-infarct area (SC) 4 weeks after infarction. Assessment of myocardial function included echocardiography 4 weeks after cell delivery. Histology was based on quantification of myocardial fibrosis, apoptosis, and capillary density.

RESULTS

Left ventricular dilatation was attenuated and ejection fraction improved significantly after cell transplantation (SM: 59.4% +/- 8.8%, SC: 60.3% +/- 6.6%, Comb: 68.2% +/- 5.6% vs control: 41.5% +/- 7.4%, P = .0013). Quantification of scar tissue showed a significant reduction of infarct area in cell-treated animals (SM: 22.3% +/- 9.1%, SC: 19.8% +/- 7.6%, Comb: 13.2% +/- 5.8% vs controls: 36.5% +/- 8.2%, P = .008). Improvement of myocardial function was associated with reduced apoptotic index (SM: 3.2% +/- 0.9%, SC: 3.1% +/- 0.6%, Comb: 1.8% +/- 0.8% vs controls: 10.3% +/- 1.6%, P = .0002) and increased vascular density (SM: 5.2 +/- 1.2, SC: 8.3 +/- 1.8, Comb: 12.3 +/- 2.3, controls: 1.9 +/- 0.3, all capillary vessels/high-power field, P = .007) in animals after cellular cardiomyoplasty.

CONCLUSIONS

Combined transplantation of skeletal myoblasts and angiopoietic progenitor cells results in ventricular function improvement, reduction of scar size and myocardial apoptosis, and increased neoangiogenesis in chronic ischemia. Clinical studies are warranted to prove this new therapeutic concept.

Intramyocardial microdepot injection increases the efficacy of skeletal myoblast transplantation

OBJECTIVE

Recent progress in the field of cellular cardiomyoplasty has opened new prospects for the treatment of ischemic heart disease and currently moves from bench to bedside. The aim of the present study was to develop a novel cell delivery technique, reducing target tissue damage and improving cell dispersion and engraftment.

METHODS

In 30 male Fischer F344 rats an infarction of the left ventricle was generated by ligation of the left anterior descendent artery. Seven days after infarction, either 15 microdepots of 10 microl myoblast cell suspension (microdepot group) or culture medium (control group) were injected into the infarcted region using an automatic pressure injection device, or three depots of 50 microl myoblast cell suspension (macrodepot group) were injected using the standard surgical technique. Echocardiography was performed in all rats before and 6 weeks after cell injection. In all groups the perioperative mortality was below 20%. Six weeks after cell transplantation, a significant improvement of ejection fraction was seen in both myoblast treated groups compared to controls (macrodepot, microdepot, control; 53.7+/-11.9, 70.7+/-2.0, 39.1+/-6.4; P=0.026, P<0.001). The microdepot group showed a more decent improvement than the macrodepot group (70.7+/-2.0 vs. 53.7+/-11.9, P=0.013). In both treated groups, grafted myoblasts differentiated into multinucleated myotubes within host myocardium, however, the engraftment pattern was different and angiogenesis was enhanced in the microdepot group.

CONCLUSIONS

Intramyocardial multisite pressure injection allows the safe and reliable transplantation of several myoblast microdepots into an infarcted myocardium and improves the efficacy of myoblast transplantation compared to the standard technique.

Stammzelltherapie der Harninkontinenz

Experimental and clinical studies investigated whether urinary incontinence can be effectively treated with transurethral ultrasound-guided injections of autologous myoblasts and fibroblasts.This new therapy was performed in eight female pigs. It could be shown that the injected cells survived well and that new muscle tissue was formed. Next, 42 patients (29 women, 13 men) suffering from urinary stress incontinence were treated. The fibroblasts were mixed with a small amount of collagen as carrier material and injected into the urethral submucosa to treat atrophies of the mucosa. The myoblasts were directly injected into the rhabdosphincter to reconstruct the muscle and to heal morphological and functional defects. In 35 patients urinary incontinence could be completely cured. In seven patients who had undergone multiple surgical procedures and radiotherapy urinary incontinence improved. No side effects or complications were encountered postoperatively. The experimental as well as the clinical data clearly demonstrate that urinary incontinence can be treated effectively with autologous stem cells. The present data support the conclusion that this new therapeutic concept may represent a very promising treatment modality in the future.

A comparative study of three different biomaterials in the engineering of skeletal muscle using a rat animal model

Defects caused by traumatic or postsurgical loss of muscle mass may result in severe impairments of the functionality of skeletal muscle. Tissue engineering represents a possible approach to replace the lost or defective muscle. The aim of this study was to compare the suitability of three different biomaterials as scaffolds for rat myoblasts, using a new animal model. PKH26-fluorescent-stained cultured rat myoblasts were either seeded onto polyglycolic acid meshes or, alternatively, suspended in alginate or in hyaluronic acid-hydrogels. In each of the eight Fisher CDF-344 rats, four capsule pouches were induced by subcutaneous implantation of four silicone sheets. After two weeks the silicone sheets were removed and myoblast-biomaterial-constructs were implanted in the preformed capsules. Specimens were harvested after four weeks and examined histologically by H&E-staining and fluorescence microscopy. All capsules were well-vascularized. Implanted myoblasts fused by forming multinucleated myotubes. This study demonstrates that myoblasts seeded onto different biomaterials can be successfully transplanted into preformed highly vascularized capsule pouches. Our animal model has paved the way for studies of myoblast-biomaterial transplantations into an ectopic non-muscular environment.

On the fate of skeletal myoblasts in a cardiac environment: down-regulation of voltage-gated ion channels

We have analysed the voltage-gated ion channels and fusion competence of skeletal muscle myoblasts labelled with green fluorescent protein (GFP) and the membrane dye PKH transplanted into the infarcted myocardium of syngenic rats. After cell transplantation the animals were killed and GFP(+)-PKH(+) myoblasts enzymatically isolated for subsequent studies of ionic currents through voltage-gated sodium, calcium and potassium channels. A down-regulation of all three types of ion channels after engraftment was observed. The fraction of cells with calcium (68%) and sodium channels (65%) declined to zero within 24 h and 1 week, respectively. Down-regulation of potassium currents (90% in control) occurred within 2 weeks to about 30%. Before injection myoblasts expressed predominantly transient outward potassium channels whereas after isolation from the myocardium exclusively rapid delayed rectifier channels. The currents recovered completely between 1 and 6 weeks under cell culture conditions. The down-regulation of ion channels and changes in potassium current kinetics suggest that the environment provided by infarcted myocardium affects expression of voltage-gated ion channels of skeletal myoblasts.

Combined transplantation of skeletal myoblasts and bone marrow stem cells for myocardial repair in rats

OBJECTIVES

To prove whether intramyocardial transplantation of combined skeletal myoblasts (SM) and mononuclear bone marrow stem cells is superior to the isolated transplantation of these cell types after myocardial infarction in rats.

METHODS

In 67 male Fischer rats myocardial infarction was induced by direct ligature of the LAD. Seven days postinfarction baseline echocardiography and intramyocardial cell transplantation were performed. Via lateral thoracotomy 200 microl containing either 10(7) SMs or 10(7) bone marrow-derived mononuclear cells (BM-MNC) or a combination of 5x10(6) of both cell types (MB) were injected in 10-15 sites in and around the infarct zone. In controls (C) 200 microl of cell-free medium were injected in the same manner. Before injection both cell types were stained using a fluorescent cell linker kit (PKH, Sigma). In addition, SMs were transfected with green fluorescent protein. Nine weeks postinfarction follow-up echocardiography was performed and animals were sacrificed for further analysis.

RESULTS

At baseline echocardiography there was no difference in left ventricular ejection fraction (LVEF; C, SM, BM-MNC, MB: 60.1+/-3.2, 53.3+/-10.2, 53.1+/-8.7, 49+/-9.0%) and left ventricular end diastolic diameter (LVEDD; C, SM, BM-MNC, MB: 6.5+/-0.8, 5.17+/-0.8, 5.77+/-1.4, 6.25+/-0.8 mm) between the different therapeutic groups. Eight weeks after cell transplantation LVEDD was significantly increased in all animals except those that received a combination of myoblasts and bone marrow stem cells (MB; C, SM, BM-MNC, MB: 7.7+/-0.6 mm, P=0.001; 7.7+/-1.5 mm, P<0.001; 7.7+/-1.1 mm, P=0.005; 6.6+/-1.7 mm, P=0.397. At the same time LVEF decreased significantly in the control group (C), stayed unchanged in animals that received bone marrow stem cells (BM-MNC) and increased in animals that received myoblasts (SM) and a combination of both cell types (MB; C, SM, BM-MNC, MB: 45.3+/-7.0%, P=0.05; 63.9+/-15.4%, P=0.044; 54.3+/-6.3%, P=0.607; 63.0+/-11.5%, P=0.039).

CONCLUSIONS

The present data show that the concept of combining SMs with bone marrow-derived stem cells may be of clinical relevance by merging the beneficial effects of each cell line and potentially reducing the required cell quantity. Further studies are required to identify the exact mechanisms underlying this synergy and to allow full exploitation of its therapeutic potential.

Membrane properties of single muscle cells of the rhabdosphincter of the male urethra

BACKGROUND

The electrophysiological properties of myoblast cultures established from the human and porcine rhabdosphincter (RS) and porcine lower limb muscle (LLSKM) were studied to elucidate their potential for tissue engineering applications in the lower urinary tract.

METHODS

Muscle biopsies were collected from the prostatic part of the RS, the RS of male pigs, and the porcine LLSKM. Ion channels were studied by means of the patch-clamp technique.

RESULTS

Only one subtype each of voltage gated Na+ and Ca2+ channels was observed in porcine RS and LLSKM. Two types of voltage gated Ca2+ channels were identified in human RS cells. The porcine RS and LLSKM myoblasts displayed similar fusion competence.

CONCLUSIONS

Porcine RS and LLSKM myoblasts and human RS and human skeletal muscle cells show a high degree of similarity. Injection of autologous skeletal muscle myoboblasts in the lower urinary tract might, therefore, represent a promising approach to treat stress incontinence after radical prostatectomy.

Inactivation determinants in segment IIIS6 of Ca(v)3.1

1. Low threshold, T-type, Ca(2+) channels of the Ca(v)3 family display the fastest inactivation kinetics among all voltage-gated Ca(2+) channels. The molecular inactivation determinants of this channel family are largely unknown. Here we investigate whether segment IIIS6 plays a role in Ca(v)3.1 inactivation as observed previously in high voltage-activated Ca(2+) channels. 2. Amino acids that are identical in IIIS6 segments of all Ca(2+) channel subtypes were mutated to alanine (F1505A, F1506A, N1509A, F1511A, V1512A, F1519A, FV1511/1512AA). Additionally M1510 was mutated to isoleucine and alanine. 3. The kinetic properties of the mutants were analysed with the two-microelectrode voltage-clamp technique after expression in Xenopus oocytes. The time constant for the barium current (I(Ba)) inactivation, tau(inact), of wild-type channels at -20 mV was 9.5 +/- 0.4 ms; the corresponding time constants of the mutants ranged from 9.2 +/- 0.4 ms in V1512A to 45.7 +/- 5.2 ms (4.8-fold slowing) in M1510I. Recovery at -80 mV was most significantly slowed by V1512A and accelerated by F1511A. 4. We conclude that amino acids M1510, F1511 and V1512 corresponding to previously identified inactivation determinants in IIIS6 of Ca(v)2.1 (Hering et al. 1998) have a significant role in Ca(v)3.1 inactivation. These data suggest common elements in the molecular architecture of the inactivation mechanism in high and low threshold Ca(2+) channels.

Amino Acids in Segment IVS6 and β-Subunit Interaction Support Distinct Conformational Changes during Cav2.1 Inactivation

Ca(v)2.1 mediates voltage-gated Ca2+ entry into neurons and the release of neurotransmitters at synapses of the central nervous system. An inactivation process that is modulated by the auxiliary beta-subunits regulates Ca2+ entry through Ca(v)2.1. However, the molecular mechanism of this alpha1-beta-subunit interaction remains unknown. Herein we report the identification of new determinants within segment IVS6 of the alpha(1)2.1-subunit that markedly influence channel inactivation. Systematic substitution of residues within IVS6 with amino acids of different size, charge, and polarity resulted in mutant channels with rates of fast inactivation (k(inact)) ranging from a 1.5-fold slowing in V1818I (k(inact) = 0.98 +/- 0.09 s(-1) compared with wild type alpha(1)2.1/alpha2-delta/beta1a k(inact) = 1.35 +/- 0.25 s(-1) to a 75-fold acceleration in mutant M1811Q (k(inact) = 102 +/- 3 s(-1). Coexpression of mutant alpha(1)2.1-subunits with beta(2a) resulted in two different phenotypes of current inactivation: 1) a pronounced reduction in the rate of channel inactivation or 2) an attenuation of a slow component in I(Ba) inactivation. Simulations revealed that these two distinct inactivation phenotypes arise from a beta2a-subunit-induced destabilization of the fast-inactivated state. The IVS6- and beta2a-subunit-mediated effects on Ca(v)2.1 inactivation are likely to occur via independent mechanisms.