Alpha-thalassemia intellectual disability: variable phenotypic expression among males with a recurrent nonsense mutation - c.109C>T (p.R37X)

Alpha-thalassemia intellectual disability, one of the recognizable X-linked disability syndromes, is characterized by short stature, microcephaly, distinctive facies, hypotonic appearance, cardiac and genital anomalies, and marked skewing of X-inactivation in female carriers. With the advent of next generation sequencing, mutations have been identified that result in less severe phenotypes lacking one or more of these phenotypic manifestations. Here we report five unrelated kindreds in which a c.109C>T (p.R37X) mutation segregates with a variable but overall milder phenotype. The distinctive facial appearance of alpha-thalassemia intellectual disability was present in only one of the 18 affected males evaluated beyond the age of puberty, although suggestive facial appearance was present in several during infancy or early childhood. Although the responsible genetic alteration is a nonsense mutation in exon 2 of ATRX, the phenotype appears to be partially rescued by the production of alternative transcripts and/or other molecular mechanisms.

Research challenges in central nervous system manifestations of inborn errors of metabolism

The Research Challenges in CNS Manifestations of Inborn Errors of Metabolism workshop was designed to address challenges in translating potential therapies for these rare disorders, and to highlight novel therapeutic strategies and innovative approaches to CNS delivery, assessment of effects and directions for the future in the treatment of these diseases. Therapies for the brain in inborn errors represent some of the greatest challenges to translational research due to the special properties of the brain, and of inborn errors themselves. This review covers the proceedings of this workshop as submitted by participants. Scientific, ethical and regulatory issues are discussed, along with ways to measure outcomes and the conduct of clinical trials. Participants included regulatory and funding agencies, clinicians, scientists, industry and advocacy groups.

A deprivation index for health planning in Canada

Administrative databases in the Canadian health sector do not contain socio-economic information. To facilitate the monitoring of social inequalities for health planning, this study proposes a material and social deprivation index for Canada. After explaining the concept of deprivation, we describe the methodological aspects of the index and apply it to the example of premature mortality (i.e. death before the age of 75). We illustrate variations in deprivation and the links between deprivation and mortality nationwide and in different geographic areas including the census metropolitan areas (CMAs) of Toronto, Montréal and Vancouver; other CMAs; average-size cities, referred to as census agglomerations (CAs); small towns and rural communities; and five regions of Canada, namely Atlantic, Quebec, Ontario, the Prairies and British Columbia. Material and social deprivation and their links to mortality vary considerably by geographic area. We comment on the results as well as the limitations of the index and its advantages for health planning.

A deprivation index for health planning in Canada

Administrative databases in the Canadian health sector do not contain socio-economic information. To facilitate the monitoring of social inequalities for health planning, this study proposes a material and social deprivation index for Canada. After explaining the concept of deprivation, we describe the methodological aspects of the index and apply it to the example of premature mortality (i.e. death before the age of 75). We illustrate variations in deprivation and the links between deprivation and mortality nationwide and in different geographic areas including the census metropolitan areas (CMAs) of Toronto, Montréal and Vancouver; other CMAs; average-size cities, referred to as census agglomerations (CAs); small towns and rural communities; and five regions of Canada, namely Atlantic, Quebec, Ontario, the Prairies and British Columbia. Material and social deprivation and their links to mortality vary considerably by geographic area. We comment on the results as well as the limitations of the index and its advantages for health planning.

[Modulation of skeletal muscle contraction by the non-toxic fraction of Buthus occitanus tunetanus venom via the cholinergic receptors]

Cholinergic receptors have an essential physiological role in the central nervous system because of their implication in higher functions in the neuromuscular junction within the brain and also in the peripheral nervous system by activating nicotinic (nAChRs) or muscarinic (mAChRs) receptors. Moreover, cholinergic receptors could be recognized by animal toxins isolated from snake venoms or alkaloids having animal or vegetal origin. In this context, we aim to find such molecules in a non toxic venom fraction of Buthus occitanus tunetanus scorpion, M1, which could therefore constitute promising medical tool. We present here a physiological study in skeletal muscle cells that regroups data that have been recently published and some new results reinforcing the last ones. The global effect of M1, was firstly studied on isolated nerve-muscle preparation. In cultured myotubes, we have found that the intracellular calcium increase, induced by M1 was blocked when ryanodine or inositol 1,4,5-triphosphate receptors are inhibited. Moreover, we have shown that M1 application on myotubes, induced a membrane depolarization as seen with acetylcholine. The treatment of myotubes with alpha-bungarotoxin blocked in most parts the depolarization amplitude. Thus, these results confirm the presence of at least one component in M1 active in nAChRs.

Effects of two medicinal plants Psidium guajava L. (Myrtaceae) and Diospyros mespiliformis L. (Ebenaceae) leaf extracts on rat skeletal muscle cells in primary culture

Crude decoction, aqueous and ethanolic extracts of two medicinal plants (Psidium guajava and Diospyros mespiliformis), widely used in the central plateau of Burkina Faso to treat many diseases were evaluated for their antagonistic effects on caffeine induced calcium release from sarcoplasmic reticulum of rat skeletal muscle cells. These different extracts showed a decrease of caffeine induced calcium release in a dose dependent manner. Comparison of the results showed that Psidium guajava leaf extracts are more active than extracts of Diospyros mespiliformis and that crude decoctions show better inhibitory activity. The observed results could explain their use as antihypertensive and antidiarrhoeal agents in traditional medicine, by inhibiting intracellular calcium release.

Regulation of store-operated calcium entries and mitochondrial uptake by minidystrophin expression in cultured myotubes

Defective expression of dystrophin in muscle cells is the primary feature of Duchenne muscular dystrophy (DMD), which is accompanied by fiber necrosis and intracellular calcium mishandling. These features led to the hypothesis that dystrophin could control calcium movements. Calcium mishandling in human DMD myotubes is dependent on contraction and/or calcium release activity, suggesting the involvement of channels being activated during these processes. Forced expression of minidystrophin at the plasma membrane of dystrophin-deficient Sol8 myotubes reactivates appropriate sarcolemmal expression of dystrophin-associated proteins and results in normal calcium homeostasis. In active dystrophic myotubes, store-operated calcium channels could be responsible for a sustained calcium influx in muscle cells. We show here that depletion of calcium stores (sarcoplasmic reticulum) by repetitive activation of calcium release and blockade of SERCA leads to a calcium influx. In myotubes expressing recombinant minidystrophin, these store-dependent influxes were reduced to a level similar to that observed in myotubes expressing native dystrophin. High store-dependent calcium influxes in dystrophin-deficient myotubes were associated with sustained cytosolic calcium transients and high intramitochondrial entries, while lower store-dependent calcium influx in myotubes expressing minidystrophin resulted in shorter calcium transients and reduced calcium uptake into mitochondria. We propose that minidystrophin negatively regulates sarcolemmal store-dependent calcium channels, which reduces store-dependent calcium influx, as well as its mitochondrial uptake. Forced expression of minidystrophin in dystrophic cells might restore the regulation of sarcolemmal store-dependent channels, which could protect against calcium mishandling.

Which biologic valve should we select for the 45- to 65-year-old age group requiring aortic valve replacement?

OBJECTIVE

The diversity of biologic valves available to replace the aortic valve renders selection difficult for the 45- to 65-year-old patient. To evaluate and compare the results of biologic valves in the 45- to 65-year-old patient, we reviewed our experience (1991-2004).

METHODS

Three hundred thirty-two patients between 45 and 65 years old with isolated aortic valve disease had a biologic valve implanted: Freestyle valve in 140 patients, a homograft in 54 patients, a stented Mosaic or Perimount valve (stented xenograft) in 62 patients, and a Ross procedure in 76 patients.

RESULTS

Perioperative mortality was comparable for all groups (Freestyle, 2.1%; homograft, 3.7%; stented xenograft, 3.2%; Ross procedure, 1.3%; P = .8). Echocardiographically determined valve performance at discharge was significantly enhanced in the Ross procedure and homograft groups (indexed effective orifice area: Freestyle, 0.9 +/- 0.3 cm 2 /m 2 ; homograft, 1.3 +/- 0.3 cm 2 /m 2 ; stented xenograft, 0.8 +/- 0.2 cm 2 /m 2 ; Ross procedure, 1.4 +/- 0.4; P < .0001; mean gradient: Freestyle, 12.0 +/- 6.6 mm Hg; homograft, 7.4 +/- 4.0 mm Hg; stented xenograft, 15.4 +/- 5.4 mm Hg; Ross procedure, 4.6 +/- 3.2 mm Hg; P < .0001). For all yearly follow-up, freedom from New York Heart Association class III or IV was comparable and greater than 95% for all groups. At 7 years, cardiac survival (homograft, 96.3% +/- 3.7%; Ross procedure, 90.6% +/- 6.3%; stented xenograft, 86.0% +/- 10.3%; Freestyle, 89.2% +/- 10.8%; P = .7) and freedom from reoperation (Ross procedure, 98.5% +/- 1.4%; homograft, 90.6% +/- 5.7%; Freestyle, 88.0% +/- 4.9%; stented xenograft, 90.0% +/- 8.0%; P = .4) were comparable. Freedoms from significant bleeding events, valve-related neurologic events, or endocarditis were comparable and greater than 95% for all groups.

CONCLUSION

Type of aortic biologic valve for the 45- to 65-year-old patient does not affect midterm survival or valve-related morbidity. Thus the choice of biologic valve for the 45- to 65-year-old patient should be dictated by patient-surgeon preference, ease of implantation, and reoperation until longer comparative studies are available.

Calcium sparks in muscle cells: interactive procedures for automatic detection and measurements on line-scan confocal images series

In muscle cells, force development is controlled by Ca2+ ions, which are rapidly released from the sarcoplasmic reticulum (SR) during sarcolemmal depolarization. In addition to this synchronized spatially homogeneous calcium signal, localized quantal Ca2+ release events (sparks) have been recorded using laser scanning confocal fluorescence microscopy. Previously, algorithms without user intervention have been developed to automatically detect and analyse sparks on confocal line-scan (space-time: 512 x 512 pixels) single images. Here we present a computer program that we called "HARVest of Elementary Events" (HARVELE) developed to both analyse events on series of confocal images and follow sparks morphology from one site during several seconds. HARVELE, coded in the image-processing language IDL 5.3., can be applied on series of n images (512 x 512 x n) obtained from the same scanning line. Computing simultaneously entire series of images allows to measure, for each release site, the frequency and the morphology of release with the conventional amplitude, size, time and duration parameters defined for sparks analysis. The use of these procedures rapidly provides much information about the properties of calcium release sites in muscle cells population and can be applied on any elementary calcium events whatever the type of cell.

Novel glycosaminoglycan mimetic (RGTA, RGD120) contributes to enhance skeletal muscle satellite cell fusion by increasing intracellular Ca2+ and calpain activity

Glycosaminoglycans (GAG) are classes of molecules that play an important role in cellular processes. The use of GAG mimetics called regenerating agent (RGTA) represents a tool to investigate the effect of GAG moiety on cellular behavior. A first member of the RGTA family (RG1192), a dextran polymers with defined amounts of sulfate, carboxymethyl, as well as hydrophobic groups (benzylamide), was shown to stimulate skeletal muscle repair after damage and myoblast differentiation. To obtain a comprehensive insight into the mechanism of action of GAG mimetics, we investigated the effect on myoblast differentiation of a novel RGTA, named RGD120, which was devoid of hydrophobic substitution and had ionic charge similar to heparin. Myoblasts isolated from adult rat skeletal muscles and grown in primary cultures were used in this study. We found that chronic treatment with RGD120 increased the growth of adult myoblasts and induced their precocious fusion into myotubes in vitro. It also partially overcame the inhibitory effect of the calpain inhibitor N-acetyl-leu-leu-norleucinal (ALLN) on these events. Western blot and zymography analyses revealed that milli calpain was slightly increased by RGD120 chronic treatment. In addition, using fluorescent probes (Indo-1 and Boc-leu-met-MAC), we demonstrated that RGD120 added to prefusing myoblast cultures accelerates myoblast fusion into myotubes, induced an increase of cytosolic free calcium concentration, and concomitantly an increase of intracellular calpain protease activity. Altogether, these results suggested that the efficiency of RGD120 in stimulating myogenesis might be in part explained through its effect on calcium mobilization as well as on the calpain amount and activity.

Underreporting of vertebral fractures on routine chest radiography

OBJECTIVE

Osteoporosis is underdiagnosed and therefore undertreated. We determined the potential usefulness of chest radiography for detecting clinically important vertebral fractures by performing semiquantitative reviews and quantitative digital morphometry on 100 routine chest radiographs taken in the emergency department and comparing the yield of these independent reviews with official radiology reports.

MATERIALS AND METHODS

One hundred randomly selected chest radiographs of patients 60 years or older who presented to the emergency department of a tertiary care hospital were evaluated. Radiographs were selected without knowledge of the presenting complaint and were independently reviewed by two board-certified radiologists and a radiology resident. A validated semiquantitative method was used to assess lateral chest radiographs for vertebral fracture. In addition, quantitative digital morphometry was undertaken. A clinically important vertebral fracture was defined as one that was at least moderate to severe (loss of height >or=> 25%).

RESULTS

Mean age of the population was 75 years, 47% were women, and 46% were admitted to the hospital. According to the reference radiologist, prevalence of moderate to severe vertebral fractures was 22%. Simple agreement was 87-88% among reviewers; kappa values were moderate (0.56-0.58). The greatest agreement was between the reference standard radiologist and quantitative digital morphometry (89% agreement; kappa = 0.67). Only 55% (12/22) of vertebral fractures we identified were mentioned in the official radiology reports.

CONCLUSION

Chest radiography has potential as a screening tool for revealing previously undiagnosed vertebral fractures, although in this study only half of moderate to severe fractures that we identified were mentioned in official reports.

Na+-Ca2+ exchange activity in rat skeletal myotubes: effect of lithium ions

The whole-cell patch-clamp technique coupled with intracellular [Ca2+] measurements was used to investigate the sodium-calcium exchange mechanism in rat skeletal muscle cells in primary culture. Replacing external Na+ ions with Li+ or N-methyl-D-glucamine (NMDG+) ions generated outward currents which were correlated with significant increases of free cytosolic-calcium concentration. These results strongly argue for a functional Na+-Ca2+ exchange mechanism working in its reverse mode. Moreover, the outward currents were sensitive to the new compound KB-R7943 (10 microM), which has been shown to be a potent inhibitor of the sodium-calcium exchanger. Outward Na+-Ca2+ exchange current densities were reduced in the presence of external Li+ as compared to those measured in the presence of NMDG+. After replacing internal sodium by lithium ions, rapid changes of external lithium concentrations generated sarcolemmal currents which were accompanied by subsequent variations of intracellular calcium activity. The currents were dependent on extracellular Li+ with a half-maximal activation at 67 mM and a Hill coefficient of 2.9. This work shows that the Na+-Ca2+ exchanger is able to significantly influence the myoplasmic calcium concentration of cultured rat myotubes. On the other hand, our results suggest that Li+ ions may substitute Na+ ions to catalyse an electrogenic Li+/Ca2+ counter transport.

A single center experience with the freestyle bioprosthesis: midterm results at the Québec Heart Institute

Stentless bioprostheses show excellent early hemodynamic performance. However, longevity still remains unknown. This study reports midterm follow-up in 419 patients in which a Freestyle bioprosthesis (Medtronic Heart Valves, Minneapolis, MN) was inserted between January 1993 and January 2000 at the Quebec Heart Institute (Ste-Foy, Québec, Canada). Mean age at implantation was 68.0 +/- 8.2 years. Implantation was subcoronary in 81.9% of the patients, as a root replacement in 16.5%, and as a root inclusion in 1.7%. Mortality at 30 days was 6.2% for the whole cohort (2.8% for isolated subcoronary aortic valve replacement). Female gender, root implantation, valve sizes 19 to 21 mm, previous surgery, a history of stroke and diabetes were identified as predictors of 30-day mortality. Actuarial freedom from all death causes was 81.5% at 7 years; freedom from valve-related deaths 97.0%, and freedom from cardiac deaths 92.7%. Freedom from thromboembolic events was 86.1% at 7 years (55.1% of events were < 30 days). Freedom from endocarditis and hemorrhagic complications were respectively 98.5% and 95.6% at 7 years. Six patients required reoperations for valve explantation: 2 for endocarditis, 2 for structural dysfunction, and 2 for nonstructural dysfunction. Incidence of moderate or severe valve insufficiency at annual echocardiographic follow-up was: discharge: 0.6%; year 1: 0.7%; year 2: 1.3%; year 3: 3.3%; year 4: 3.7%; year 5: 2.6%; year 6: 0%. At 6 years after implantation, mean transvalvular gradient and effective valve orifice area were comparable to the year 1 values. This single center experience with the Medtronic Freestyle prosthesis shows preserved hemodynamic performance and low valve-related complications at midterm.

A case-control study of nonsyndromic oral clefts in Maryland

PURPOSE

Isolated, nonsyndromic oral clefts cases (n = 171) and unaffected controls (n = 182) were used to identify both genetic and environmental risk factors.

METHODS

Infants born in Maryland between 1992 to 1998 with an isolated, nonsyndromic oral cleft [cleft lip (CL), cleft lip and palate (CLP), or cleft palate (CP)] were recruited and exposure plus family history data were collected. Controls were unaffected infants. DNA was collected from all cases and their parents, plus controls.

RESULTS

No statistically significant association was found between any of the following: maternal smoking, vitamin use, urinary tract infection, or recreational drug use in either univariate analysis or after adjusting for maternal age and education. More control mothers reported alcohol use during the critical time period of pregnancy (one month before conception through the first trimester) as compared to case mothers. There was a 10-fold increase in risk to siblings of cases as compared to siblings of controls. Markers at four candidate genes were examined: transforming growth factor alpha (TGF alpha), transforming growth factor beta 3 (TGF beta 3), MSX1, and BCL3. Only MSX1 showed significant differences in allele frequencies between CP cases and controls. MSX1 also showed significant evidence of linkage disequilibrium with a susceptibility gene controlling risk for CP.

CONCLUSION

Most environmental risk factors examined here gave little evidence of association with risk to isolated, nonsyndromic oral clefts, although any alcohol consumption seemed protective. MSX1 showed evidence of linkage disequilibrium in both case-control and case-parent trio analysis.

Effects of Sclerocarya birrea (A. rich) hochst (anacardiaceae) leaf extracts on calcium signalling in cultured rat skeletal muscle cells

Sclerocarya birrea is a plant used widely to treat many diseases in Burkina Faso, although no scientific data has been reported about its mechanism of action. In the present study the effects of its leaf extracts were investigated on calcium signalling in rat cultured skeletal muscle cells. The results show that the different extracts (crude decoction, aqueous, ethanolic and chloroformic extracts) have significant antagonistic effect on caffeine-induced calcium release from sarcoplasmic reticulum. Crude decoction is the most active followed by ethanolic, aqueous and chloroformic extracts in dose-dependent manner and can partly justify the use of the plant in traditional medicine.

Calcium currents and transients in co-cultured contracting normal and Duchenne muscular dystrophy human myotubes

1. The goal of the present study was to investigate differences in calcium movements between normal and Duchenne muscular dystrophy (DMD) human contracting myotubes co-cultured with explants of rat spinal cord with attached dorsal root ganglia. Membrane potential, variations of intracellular calcium concentration and T- and L-type calcium currents were recorded. Further, a descriptive and quantitative study by electron microscopy of the ultrastructure of the co-cultures was carried out. 2. The resting membrane potential was slightly less negative in DMD (-61.4 +/- 1.1 mV) than in normal myotubes (-65.5 +/- 0.9 mV). Both types of myotube displayed spontaneous action potentials (mean firing frequency, 0.42 and 0.16 Hz, respectively), which triggered spontaneous calcium transients measured with Indo-1. 3. The time integral under the spontaneous Ca(2+) transients was significantly greater in DMD myotubes (97 +/- 8 nM s) than in normal myotubes (67 +/- 13 nM s). 4. The L- and T-type current densities estimated from patch-clamp recordings were smaller in DMD cells (2.0 +/- 0.5 and 0.90 +/- 0.19 pA pF(-1), respectively) than in normal cells (3.9 +/- 0.7 and 1.39 +/- 0.30 pA pF(-1), respectively). 5. The voltage-dependent inactivation relationships revealed a shift in the conditioning potential at which inactivation is half-maximal (V(h,0.5)) of the T- and L-type currents towards less negative potentials, from -72.1 +/- 0.7 and -53.7 +/- 1.5 mV in normal cells to -61.9 +/- 1.4 and -29.2 +/- 1.4 mV in DMD cells, respectively. 6. Both descriptive and quantitative studies by electron microscopy suggested a more advanced development of DMD myotubes as compared to normal ones. This conclusion was supported by the significantly larger capacitance of the DMD myotubes (408 +/- 45 pF) than of the normal myotubes (299 +/- 34 pF) of the same apparent size. 7. Taken together, these results show that differences in T- and L-type calcium currents between normal and DMD myotubes cannot simply explain all observed alterations in calcium homeostasis in DMD myotubes, thus suggesting that other transmembrane calcium transport mechanisms must also be altered in DMD myotubes compared with normal myotubes.

A deprivation index for health and welfare planning in Quebec

Given that one of the goals of public health policy in Quebec and Canada is to reduce social inequalities in health and welfare, it is surprising, to say the least, that most information systems in this field make no mention of people's socio-economic characteristics. The present article proposes an index to reflect the material and social dimensions of deprivation as this concept has been developed by Peter Townsend and other authors. The article describes the method used to create the index, which uses census data and tools developed by Statistics Canada to match postal codes with enumeration areas. Examples are provided of the use of the index in information systems covering three aspects of health and welfare in Quebec: deaths, hospitalizations and births. The value of the information provided by this index in planning health and social services is demonstrated.

Calcium homeostasis and cell death in Sol8 dystrophin-deficient cell line in culture

Abnormalities of calcium homeostasis are involved in the process of cell injuries such as Duchenne muscular dystrophy characterized by the absence of the protein dystrophin. But how the absence of dystrophin leads to cytosolic calcium overload is as yet poorly understood. This question has been addressed with skeletal muscle cells from human DMD muscles or mdx mice. Although easier to obtain than human muscles, mdx muscle cells have provided controversial data concerning the resting intracellular calcium level ([Ca2+](i)). This work describes the culture of Sol8 cell line that expresses neither dystrophin nor adhalin, a dystrophin-associated protein. The [Ca2+](i)and intracellular calcium transients induced by different stimuli (acetylcholine, caffeine and high potassium) are normal during the first days of culture. At later stages, calcium homeostasis exhibits drastic alterations with a breaking down of the calcium responses and a large [Ca2+](i)elevation. Concomitantly, Sol8 cells exhibit morphological signs of cell death like cytoplasmic shrinkage and incorporation of propidium iodide. Cell death could be significantly reduced by blocking the activity of calpains, a type of calcium-regulated proteases. These results suggest that Sol8 cell line provides an alternative model of dystrophin-deficient skeletal muscle cells for which a clear disturbance of the calcium homeostasis is observed in culture in association with calpain-dependent cell death. It is shown that transfection with a plasmid cDNA permits the forced expression of dystrophin in Sol8 myotubes as well as a correct sorting of the protein. This approach could be used to explore possible interactions between dystrophin deficiency, calcium homeostasis alteration, and dystrophic cell death.

Cationic channels in normal and dystrophic human myotubes

Human skeletal muscle cells obtained from normal and Duchenne muscular dystrophy patients were cocultured with explants of rat dorsal root ganglions. Single-channel recordings were performed with the cell-attached configuration of the patch-clamp technique and negative pressure was applied via the patch-pipette in order to mechanically stimulate the membrane patch. Inward elementary current activity was recorded under control or negative pressure conditions. Its occurrence and mean open probability were higher in Duchenne muscular dystrophy. Amplitude histograms reveal that these channels have a small unitary conductance of around 10 pS in 110 mM Ca2+ and could be inhibited in a dose-dependent manner by gadolinium. Results show that the membrane stress favoured calcium permeation through these channels. Taken together these data provide arguments for the involvement of such channels in calcium overload previously observed in cocultured dystrophic human (Duchenne muscular dystrophy) muscle cells.

Primitive neuroectodermal tumor of the diaphragm: a case report

We present a case of primitive neuroectodermal tumor (PNET) arising from the diaphragm in a neonate. PNETs are rare malignant tumors that belong to the group of small, round, blue-cell neoplasms of childhood. To the best of our knowledge, a PNET originating from the diaphragm has not been previously reported.

Expression of the sodium/calcium exchanger in mammalian skeletal muscle cells in primary culture

Previous investigations have demonstrated molecular and functional expression, at early phases of development of skeletal muscle cells in primary culture, of cardiac isoforms of proteins involved in calcium transport and regulation, like the L-type calcium channel. Here the expression of the cardiac isoform of the Na(+)/Ca(2+) exchanger (NCX1) was studied in skeletal muscle cells developing in vitro, by using biochemical, immunological, and electrophysiological techniques. Northern and Western blot experiments revealed the presence of this cardiac exchanger and its increasing expression during the early phases of development. Confocal imaging of myotubes showed an NCX1 distribution that was predominantly sarcolemmal. The whole-cell patch-clamp technique allowed us to record ionic currents, the direction and the amplitude of which depended on extracellular sodium and calcium concentrations. The developmental changes of this functional expression could be correlated with the molecular NCX1 expression changes. Taken together these data demonstrate the presence of the NCX1 isoform of the Na(+)/Ca(2+) exchanger during in vitro myogenesis and reinforce the theory that significant levels of cardiac-type proteins are transiently expressed during the early phases of the skeletal muscle cell development.

Infantile refsum disease in four Amish sibs

Infantile Refsum disease (IRD) appears with varying degrees of impaired vision, hearing loss, developmental delays, and neuromotor deficiencies. We report on four Amish sibs with IRD from a consanguineous marriage; biochemical testing supported the diagnosis of IRD. Of particular interest in this sibship are characteristic poorly formed yellow-orange teeth in at least three of the four affected sibs and behavior problems in the affected females.

The effect of methylprednisolone on intracellular calcium of normal and dystrophic human skeletal muscle cells

Clinical trials have shown that a glucocorticoid, the methyiprednisolone (PDN), has a beneficial effect on muscle strength and function in Duchenne muscular dystrophy (DMD) patients. The aim of this study was to test if the effect of PDN could be mediated via a possible action on intracellular calcium. The intracellular calcium activity, at rest and during calcium mobilizing drug superfusion protocols was recorded in normal and dystrophic human cocultured muscle cells. PDN (10 microM) pretreatment induced an elevation of the resting calcium concentration of 51, 34 and 38% in proliferating normal myoblasts, DMD myoblasts and DMD myotubes, respectively, while normal myotubes resting [Ca2+]i was not altered.

Polymeric gadolinium chelate magnetic resonance imaging contrast agents: design, synthesis, and properties

We have synthesized and evaluated five series of polymeric gadolinium chelates which are of interest as potential MRI blood pool contrast agents. The polymers were designed so that important physical properties including molecular weight, relaxivity, metal content, viscosity, and chelate stability could be varied. We have shown that, by selecting polymers of the appropriate MW, extended blood pool retention can be achieved. In addition, relaxivity can be manipulated by changing the polymer rigidity, metal content affected by monomer selection, viscosity by polymer shape, and chelate stability by chelator selection.

The effects of Securidaca longepedunculata root extract on ionic currents and contraction of cultured rat skeletal muscle cells

The effects of the primary extract roots of Securidaca longepedunculata were tested on sodium, calcium and potassium currents in rat skeletal muscle cells developed in culture. In addition, they were tested on depolarisation-induced contraction and resting intracellular calcium levels. S. longepedunculata extract (10(-6) g/l) increases sodium current at all potentials. No clear effect was observed on calcium current except for a slight increase at negative potentials (-30, -10 mV) revealing a 5 mV shift towards negative potentials of the I(Ca)/V curve, as with potassium current. In contrast, at the same concentration, S. longepedunculata enhanced the contractile response elicited by durable depolarisation. This was not attributable to the slight increase in resting intracellular free calcium concentration which did not change during and following S. longepedunculata application. These results strongly suggest that S. longepedunculata root extract contains one or more components acting on the voltage-sensor of excitation-contraction coupling (dihydropyridine receptors), regardless of its implication as a calcium channel.

Clinical and hemodynamic performance of the Freestyle aortic root bioprosthesis

BACKGROUND

The objective of this study is to assess the clinical and hemodynamic performance of a stentless porcine bioprosthesis, the Freestyle aortic root bioprosthesis.

METHODS

Consenting patients requiring isolated aortic valve or aortic root replacement received the Freestyle bioprosthesis. Clinical follow-up and echocardiographic data were obtained at discharge, 3 to 6 months, 1 year, and annually thereafter.

RESULTS

Two hundred seventy-six patients received a Freestyle aortic root bioprosthesis between January 1993 and July 1997. The mean age was 67.7 years. Preoperatively, 86.3% were either New York Heart Association class III or IV. Two hundred thirty-eight patients underwent valve (subcoronary) replacement, 36 underwent aortic root replacement, and 2 underwent valve replacement using the root-inclusion technique. The early mortality was 5.4%, with 3.3% mortality for the subcoronary technique and 19.4% mortality for aortic root replacement. The mean gradient decreased significantly between discharge and the 3- to 6-month follow-up and stabilized thereafter. The effective orifice area increased significantly from discharge to 3 to 6 months' follow-up. At 3 years, 84.4% of the patients had either no or trivial regurgitation.

CONCLUSIONS

The Freestyle bioprosthesis has good clinical performance and good short-term hemodynamic performance. The majority of the regurgitation identified is not clinically significant.

Hemodynamic features of the freestyle aortic bioprosthesis compared with stented bioprosthesis

BACKGROUND

The Freestyle prosthesis is a new stentless aortic bioprosthesis. Anticipated benefits are improved hemodynamics and increased longevity.

METHODS

Doppler echocardiograms were performed early and at 3 to 6 months, 1 year, and 2 years after operation in 157 patients (69 men, 88 women, aged 48 to 85 years) with this prosthesis, and results were compared with hemodynamic data in patients with Intact and Mosaic stented bioprostheses.

RESULTS

Distinctive features of the prosthesis compared with stented prostheses are (1) an increase in effective orifice area (+0.15+/-0.26 cm2; p < 0.05) and a decrease in mean gradient (-3.5+/-4.0 mm Hg; p < 0.001) during the first 3 to 6 months postoperatively and stabilization thereafter; (2) a markedly lower mean gradient at 1 year after operation (average, 6+/-4 mm Hg) than in stented prostheses (Intact, 22+/-8 mm Hg; Mosaic, 12+/-6 mm Hg); (3) in contrast to stented prostheses, in vivo effective orifice areas much lower (-0.91+/-0.35 cm2) than those calculated in vitro; (4) as in stented prostheses, the indexed effective orifice area (cm2/m2) is the best predictor (r = 0.77 at 1 year) of the mean gradient after operation; and (5) similar incidence of aortic regurgitation (trivial or mild, 34% versus 29% in Intact).

CONCLUSIONS

The hemodynamics of the Freestyle are very satisfactory and represent a marked improvement in comparison to stented prosthesis.

Antisense oligonucleotides against ‘cardiac’ and ‘skeletal’ DHP-receptors reveal a dual role for the ‘skeletal’ isoform in EC coupling of skeletal muscle cells in primary culture

Two dihydropyridine receptor mRNA isoforms (cardiac and skeletal) are expressed in rat skeletal muscle cells in primary culture. The progressive changes in excitation-contraction coupling mode from dual mode (‘skeletal’ and ‘cardiac’) to predominant ‘skeletal’ one during in vitro myogenesis are thought to be linked to the developmental changes in the relative expression of the two types of molecular entity previously observed in this preparation. In order to test this hypothesis, myotube cultures (5- to 7-day-old) were treated with antisense phosphorothioated oligodeoxynucleotides against cardiac or skeletal alpha1 subunit of L-type calcium channel. The oligodeoxynucleotide uptake by cells was checked by means of imaging of fluorescent oligodeoxynucleotide derivatives within the cells. Optimum concentration used (10 microM in the extracellular medium) and incubation time (70 hours) were empirically determined. Antisense directed against the cardiac type led to a 54% decrease in the averaged L-type calcium current peak density at −10 mV. The same type of experiment was performed with antisense against the skeletal isoform and led to a same order of inhibition (46%). This result clearly shows that the two isoforms can work as a calcium channel. Conversely, analysis of the shape of T-V (relative contractile amplitude versus membrane potential) curves shows that the treatment with ‘skeletal’ antisense depressed the contractile response in the medium membrane potential range whereas treatment with ‘cardiac’ antisense had no effect. This and other results taken together suggest that the skeletal isoform of dihydropyridine receptor is involved in both ‘cardiac’ and ‘skeletal’ types of EC coupling mechanisms at work in early stages of myotubes in vitro development. The type of coupling probably depends on the proximity of the skeletal dihydropyridine receptor and the ryanodine receptor.

Quantitative assessment of serum hepatitis B e antigen, IgM hepatitis B core antibody and HBV DNA in monitoring the response to treatment in patients with chronic hepatitis B

Virological response to treatment of chronic hepatitis B is defined as the loss of serum hepatitis B virus DNA (HBV DNA) and hepatitis B e antigen (HBeAg). The quantitative measurement of HBV DNA is useful for monitoring and predicting the response to therapy with interferon-alpha (IFN-alpha). In this study, we evaluated whether quantitative measurement of serum HBeAg and IgM antibody to hepatitis B core antigen (HBcAb) could also be used in this manner. Using a microparticle-capture enzyme immunoassay (IMx), a standard curve of fluorescence rate vs HBeAg concentration was constructed to provide quantitative results. The IgM HBcAb index was also measured using a microparticle enzyme immunoassay and serum HBV DNA was measured by a solution hybridization assay. We studied 48 patients who were initially positive for HBeAg and HBV DNA and who were treated with IFN-alpha2b. Their sera were serially evaluated for HBeAg concentration, and results were compared with HBV DNA levels. In the 14 patients who responded to IFN, similar disappearance curves were observed with good intraindividual correlation between the levels of the two markers. In the 34 non-responders, HBeAg levels decreased during treatment but never became negative; HBV DNA levels also decreased during treatment and became transiently undetectable in six patients, falsely suggesting treatment success. The IgM HBcAb index paralleled changes in alanine aminotransferase (ALT) concentration and did not provide additional information. Multiple logistic regression indicated that baseline ALT and HBeAg concentrations were independent predictors of the response to treatment and the addition of neither HBV DNA nor IgM HBcAb improved the model. We conclude that quantitative measurement of HBeAg provides information similar to that of HBV DNA in monitoring and predicting the response to treatment; this technique could be readily adaptable to clinical laboratories.

Reversal of the relative expression of cardiac and skeletal alpha1 subunit isoforms of L-type calcium channel during in vitro myogenesis

Cardiac and skeletal type of excitation-contraction coupling (ECC) are quite different. Those differences could be explained by structural ones in the molecular entities involved in ECC, ie dihydropyridines (DHP) receptors (alpha1 subunit of L-type calcium channels) of the sarcolemma or ryanodine receptors of the sarcoplasmic reticulum membrane. As previously demonstrated by means of electrophysiology, the two types of ECC coexist during the first stages of in vitro development of skeletal muscle, whereas the skeletal type predominates at the later ones. In order to see whether evolution of ECC could be correlated with the one of alpha1 subunit expression, we determined by Northern Blotting which isoforms of alpha1 subunit are expressed during the in vitro myogenesis. mRNA corresponding to the cardiac isoform are present in myoblasts (before fusion), but patch-clamp experiments showed that they are not functional. After fusion, skeletal and cardiac mRNA are coexpressed in myotubes, with different intensities: whereas expression of skeletal mRNA (which are the more intensive) stabilized at the later stages tested, cardiac mRNA decreased. We conclude that evolution in mRNA alpha1 subunit isoforms expression could partly explained evolution of ECC features during in vitro myogenesis.

Transient involvement of gap junctional communication before fusion of newborn rat myoblasts

Heptanol-sensitive gap junction communication was characterized by the gap-FRAP method (fluorescence recovery after photobleaching) in confluent rat myoblasts developing in primary culture. Cell to cell dye diffusion was mainly restricted to a short period of the perfusion lag period and disappeared during fusion promotion except between some myoblasts and myotubes. This short period of occurrence of gap junction communication might be transiently and partially involved during the first steps preparing the subsequent fusion, since treatment with an uncoupler (heptanol) reduced the formation of multinucleated myotubes. During subsequent steps, functional gap junctions are not involved between myoblasts in the process of fusing, but a possible secondary involvement for fusion of remaining myoblasts to newly-formed myotubes is discussed. These data, together with results from other authors, suggest a regulatory role of gap junction communication in development and fusion of skeletal muscle cells, by providing a pathway for exchanging small molecules from one myoblast to another.

Hypoosmotic shocks induce elevation of resting calcium level in Duchenne muscular dystrophy myotubes contracting in vitro

In Duchenne muscular dystrophy (DMD) muscle cells which lack dystrophin, contraction seems to be a dominant factor contributing to the abnormal elevated intracellular calcium level. Human normal and DMD contracting myotubes cocultured with nervous cells were exposed to a hypotonic medium to mimic contraction-induced mechanical stress on the membrane, and the cytoplasmic calcium activity was simultaneously monitored (Indo-1). Hypotonic shocks induced a reversible [Ca2+]i increase in 81% of the DMD cells vs. 54% of control. In addition, responses were qualitatively different: most of DMD myotubes displayed a fast increase of Ca2+ flowing from the edge of the myotube while the response in normal cells was slow and diffuse. The fact that these responses were not affected by ryanodine, was in favour of an external source of Ca2+ involved in the hypoosmotic shocks. The localized increase of Ca2+ in DMD myotubes, inhibited by Gd3+, could result from sites of high mechanosensitive channel activity or density which could constitute a pathway for Ca2+ entry provided these cells contract.

Myoblast fusion requires cytosolic calcium elevation but not activation of voltage-dependent calcium channels

Many studies of in vitro skeletal myogenesis have demonstrated that fusion of myoblasts into multinucleated myotubes is regulated by calcium-dependent processes. Calcium ions appear to be necessary at the outer face of the membrane, and an additional internal calcium increase seems required to promote fusion of aligned myoblasts. It has been proposed that a calcium influx could take place prior to fusion and that this may be mediated by voltage-dependent calcium channels. Previously, we showed that two types of voltage-dependent calcium currents were expressed in multinucleated myotubes but not in rat myoblasts growing in primary culture before the withdrawal of the growth medium. We also showed that the previous formation of multinucleated synticia was not a prerequisite of developmental appearance of calcium currents, suggesting that the two events were time-correlated but not sequentially dependent. These features led us to investigate changes in internal calcium activity and the possible appearance of voltage-dependent calcium influx pathways just after the promotion of fusion by the change of culture medium. The results confirm that a rise in cytosolic calcium activity occurs slightly before fusion in confluent myoblasts and remained in newly formed myotubes. Reducing this elevation by internal calcium buffering lowered myoblast fusion and, reciprocally, blocking cell fusion prevented calcium increase. Treatment with the organic calcium channel blockers nifedipine (5 microM) and PN 200-110 (1 microM) did not alter cytosolic calcium changes nor cell fusion, and voltage-dependent calcium currents were never observed by the perforated patch-clamp technique in aligned fusion-competent myoblasts. Other voltage-operated mechanisms of calcium rise were not detected since depolarization with hyperpotassium solutions failed to elicit increases in intracellular calcium. On the contrary, acetylcholine was able to promote extracellular calcium-dependent calcium transients. Our results confirm the requirement of an increase in resting calcium during fusion, but do not support the hypothesis of an influx through voltage-dependent channels or other voltage-operated pathways. The elevation of internal calcium activity may result from other mechanisms, such as a cholinergic action for example.

Properties of calcium currents and contraction in cultured rat diaphragm muscle

The characterization of calcium currents and contraction simultaneously measured in cultured rat diaphragm muscle cells was carried out in the present study. Whole-cell patch-clamp experiments were designed to further elucidate the mechanism of excitation-contraction (E-C) coupling in diaphragm which, though generally considered a skeletal-type muscle, has been reported to exhibit properties indicative of a cardiac-like E-C coupling mechanism. Normalized current/voltage (I/V) curves for two concentrations of external calcium (2.5 and 5 mM) were obtained from diaphragm myoballs. Both curves showed peaks corresponding to the activation of a T-type calcium current and a dihydropyridine-sensitive L-type calcium current. The normalized curve for the voltage dependence of the activation of contraction in diaphragm myoballs followed a typical Boltzmann-type relationship to the peak of contraction. Thereafter, the curve declined in a manner that was more pronounced in diaphragm compared to that measured in additional experiments using cultured rat limb muscle myoballs. This effect could be interpreted in terms of a more pronounced participation of the L-type current in E-C coupling in cultured diaphragm muscle. An increased likelihood of cultured diaphragm muscle to undergo depletion of sarcoplasmic reticular calcium stores during repetitive stimulation, or a heightened propensity for the voltage sensor for E-C coupling in diaphragm to enter the inactive state could also explain this effect. Maximal contractile activity was only slightly affected when the L-type current was blocked by externally applied cadmium (2 mM) or cobalt (3 mM), suggesting that a pronounced calcium-current-dependent component of contraction is unlikely in cultured diaphragm muscle. These results show that T- and L-type calcium channels are expressed in cultured rat diaphragm muscle cells and that, in contrast to cardiac muscle, the entry of calcium ions via L-type voltage-dependent calcium channels is not a prerequisite for contraction. Differences in the voltage sensitivity of contraction, observed at depolarized membrane potentials in cultured rat diaphragm and limb muscle cells, suggest that the voltage sensor for E-C coupling in diaphragm might more readily enter an inactivated configuration - possibly by a mechanism which is dependent on the concentration of external calcium.

Abnormal calcium homeostasis in Duchenne muscular dystrophy myotubes contracting in vitro

Resting intracellular calcium activity was recorded in three kinds of human muscle cells in culture: normal (control) and dystrophic (DMD and FSH), by means of a ratiometric fluorescence method using the calcium probe Indo-1 under laser illumination. DMD cells are characterized by a lack of dystrophin whereas FSH cells express normal dystrophin. The aim of this study was to determine whether, in dystrophin-deficient muscle cells (DMD), contraction destabilized internal calcium homeostasis. Muscle cells were cocultured with rat spinal cord explants to improve the maturation of human myotubes up to the stage where contraction appears. The resting intracellular calcium level was significantly higher in contracting DMD cells (107 +/- 8 nM; n = 44) compared to control cells (66 +/- 6 nM; n = 43) or in FSH cells (56 +/- 6 nM; n = 35). DMD myotubes cocultured in the presence of TTX which inhibited contractile activity, did not develop an increase in free cytosolic Ca2+ concentration. The amplitudes of calcium transients elicited by exposure to acetylcholine (ACh) or high K+ medium (100K) were significantly higher in contracting DMD myotubes than in control ones. The extra-responses were not observed in DMD myotubes cocultured with TTX. This study strongly suggest that: (i) contraction is a dominant factor contributing to Ca2+ abnormalities in DMD cells; and (ii) contracting dystrophin-deficient cells have defective calcium handling mechanisms during electrical events which involve sarcolemma.

Aortic valve replacement with pulmonary autograft in children and adults

Aortic valve replacement with a conventional prosthesis is still flawed with complications, especially in children and young adults. Complex aortic root enlargement (Konno) is often needed because of small aortic diameter. The poor compliance with anticoagulation by teenagers and the risks associated with this made us look at alternative techniques. From November 1990 to June 1994, 70 patients were considered for pulmonary autografts in our institution; 64 underwent the procedure with one death and one failure to implant. Short-term results are excellent, with minimal gradient in 90% and minimal regurgitation in 96% of the patients. The long-term follow-up, hopefully, will confirm the superiority of this procedure over more conventional replacement.

Medtronic Intact porcine bioprosthesis: clinical performance to seven years

The clinical performance of the Medtronic Intact porcine bioprosthesis was evaluated in 1,084 patients (mean age 66.4 years, range 9 to 91 years) who had a total of 1,099 implantations between 1985 and 1992, inclusive. There were 709 aortic valve replacements, 297 mitral valve replacements, and 80 multiple valve replacements. Concomitant procedures were performed in 432 (39.3%). The age group distribution (years) was 35 or younger in 20 patients, 36 to 50 in 64, 51 to 64 in 274, 65 to 69 in 225, 70 or older in 500. The total follow-up time was 2,741 patient-years (mean, 2.5 years) and was 97.5% complete. The early mortality rate was 7.1% and late mortality was 3.9% per patient-year. The overall patient survival at 7 years was 70% +/- 3%. The freedom from major thromboembolism was 94% +/- 1% at 7 years (p = not significant for valve positions). The freedom from reoperation at 7 years was 93% +/- 1%; freedom from valve-related mortality was 89% +/- 2%. The freedom from structural valve deterioration at 7 years was 97% +/- 1% (aortic valve replacement 97% +/- 1%; mitral valve replacement 97% +/- 2%). The freedom from structural valve deterioration among age groups was not different for the overall population, aortic valve replacement, or mitral valve replacement. Hemodynamic assessment revealed obstructive properties for aortic valve replacement sizes of 21 and 23 mm and for mitral valve replacement sizes of 25 and 27 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Phenotype of patients with peroxisomal disorders subdivided into sixteen complementation groups

OBJECTIVE

To use the technique of complementation analysis to help define genotype and classify patients with clinical manifestations consistent with those of the disorders of peroxisome assembly, namely the Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), infantile Refsum disease (IRD), and rhizomelic chondrodysplasia punctata (RCDP).

STUDY DESIGN

Clinical findings, peroxisomal function, and complementation groups were examined in 173 patients with the clinical manifestations of these disorders.

RESULTS

In 37 patients (21%), peroxisome assembly was intact and isolated deficiencies of one of five peroxisomal enzymes involved in the beta-oxidation of fatty acids or plasmalogen biosynthesis were demonstrated. Ten complementation groups were identified among 93 patients (54%) with impaired peroxisome assembly and one of three phenotypes (ZS, NALD, or IRD) without correlation between complementation group and phenotype. Forty-three patients (25%) had impaired peroxisome assembly associated with the RCDP phenotype and belonged to a single complementation group. Of the 173 patients, 10 had unusually mild clinical manifestations, including survival to the fifth decade or deficits limited to congenital cataracts.

CONCLUSIONS

At least 16 complementation groups, and hence genotypes, are associated with clinical manifestations of disorders of peroxisome assembly. The range of phenotype is wide, and some patients have mild involvement.

Myoblast fusion is not a prerequisite for the appearance of calcium current, calcium release, and contraction in rat skeletal muscle cells developing in culture

During in vitro development of rat skeletal muscle cells, contraction and calcium currents progressively appear after fusion of myoblasts. To investigate whether muscle-specific functions are expressed in the absence of myoblast fusion, rat neonatal muscle cells were cultured in a differentiation medium under conditions that are well known to inhibit fusion: prolonged culture in a low-calcium medium or treatment with cytochalasin B. We have demonstrated that the fusion-arrested cells expressed differentiative properties in L-type calcium current, transient release of calcium ions from internal stores in response to caffeine and depolarizing agents, and contraction elicited by depolarization. Properties and potential-dependence of L-type calcium currents were similar to that in control fused cells, but T-type calcium currents were not observed, while both types coexist in myotubes. Properties of calcium transients and voltage dependence of contraction suggested that the excitation-contraction mechanisms were well established. However, comparing to well-developed myotubes at the same time of culture, the characteristics of calcium transients and contraction of fusion-arrested cells were closer to those of younger myotubes, which can be interpreted in terms of a delay in maturation of excitation-contraction coupling and contractile machinery. All these observations demonstrate that myoblast fusion is not necessary for triggering the establishment of calcium transport and release and contractile functions of rat muscle cells developing in culture. The appearance of muscle-specific functions is consistent with previous results demonstrating that the fusion-arrested cells express muscle-specific proteins and structures.

Cultured rat skeletal muscle cells treated with cytochalasin exhibit normal dystrophin expression and intracellular free calcium control

Many studies performed to elucidate the molecular and cellular processes involved in muscular dystrophies have led to the working hypothesis of a key role for the cytoskeleton elements linking the extracellular matrix to myofibrils. It was recently suggested that cytochalasin B treatment of mouse soleus muscle promoted cell damage mediated by a cytosolic increase in free calcium concentration. Since intracellular calcium overload may be a primary event resulting from the alteration of cytoskeletal structure, this study was intended to evaluate whether or not the integrity of the F-actin microfilament network is necessary for calcium homeostasis. The developmental establishment of the normal cytoarchitecture was altered by treatment of myoblasts with the actin-disrupting agents cytochalasin B and D, and the effects were compared with those in myoblasts treated with colchicine. These drugs modified the morphogenesis in that they prevented the formation of elongated myotubes by myoblast fusion, but did not prevent the maturation of contractile myogenic cells. The subcellular organisation of actin filaments visualised by confocal fluorescence microscopy was modified by colchicine and cytochalasins, but appearance of contractile apparatus and mechanical activity were not precluded. Sarcolemmal addressing of dystrophin, the subsarcolemmal protein lacking in Duchenne muscular dystrophy, was not prevented by cytochalasin. The evaluation of the basal activity of cytosolic calcium measured with indo-1 suggested that the disruption of actin or microtubules did not prevent developing muscle cells to maintain a low basal calcium activity. We propose that the global integrity of the cytoskeleton network is not crucial for the maintenance of calcium homeostasis in muscle cells developing in vitro. These results are discussed with regard to current theories attempting to understand the functional consequences of an abnormal expression of the dystrophin-glycoprotein complex interacting with the extracellular matrix and the cytoskeleton.

Developmental changes in Ca2+ currents from newborn rat cardiomyocytes in primary culture

Electrophysiological characteristics of neonatal rat ventricular cardiomyocytes in primary culture were studied using the whole-cell patch-clamp recording technique. Cell size, estimated by measurement of membrane capacitance, was significantly increased throughout the culture from 22.4 +/- 5.4 pF at day 2 to 55.0 +/- 16.1 pF at day 7, reflecting the hypertrophic process which characterises postnatal cell development. The Ca2+ current was investigated at day 2 and 7 of the culture which constituted the early postnatal and maximally developed stages, respectively, of isolated cells in our experimental conditions. At 2 days of culture, two types of Ca2+ current could be distinguished, as also observed in freshly dissociated newborn ventricular cells. From their potential dependence and pharmacological characteristics, they could be attributed to the T- (ICa-T) and L-type (ICa-L) Ca2+ current components. After 7 days of culture, only the latter ICa-L was present and its density was significantly increased when compared to the density in 2-day-old cells, but lower than that obtained in freshly dissociated adult cells. As the age of the culture progressed, the steady-state inactivation curve was shifted toward negative potentials, in the direction of the inactivation curve obtained for adult cells. Compared to the serum-free control conditions, the density of ICa-L was significantly increased in the presence of fetal calf serum throughout the culture. Consequently, the density of ICa-L obtained in 7-day-old cells was similar to the density of ICa-L obtained in freshly dissociated adult cardiac cells.(ABSTRACT TRUNCATED AT 250 WORDS)