The biochemistry and molecular biology of the dihydropyridine-sensitive calcium channel

Unveiling the antibacterial efficacy of thiazolo [3,2-a] pyrimidine: Synthesis, molecular docking, and molecular dynamic simulation

Two series of C-Mannich base derivatives were synthesized and evaluated through the reaction of formaldehyde, two thiazolo-pyrimidine compounds, and various 2°-amines. The chemical structures and inherent properties of the synthesized compounds were authenticated using a variety of spectroscopic techniques. The aseptic bactericidal potential of the compounds was assessed alongside five common bacterial microbes, with Ampicillin employed as the reference drug. Compounds 9b and 9d demonstrated comparable antibacterial activity to ampicillin against Bacillus subtilis and Bacillus megaterium, respectively, at 100 μg/mL. Furthermore, compounds 9f and 10f exhibited noteworthy action against Staphylococcus aureus (MIC: 250 μg/mL). Compounds 10b and 10f displayed excellent efficacy versus Escherichia coli, boasting (MIC: 50 μg/mL). Molecular docking studies elucidated the necessary connections and energies of molecular entities with the E. coli DNA gyrase B enzyme, a pivotal target in bacterial DNA replication. Further thermodynamic stability of the ligand-receptor complex of 10b and 10f were further validated though 200 ns molecular dynamics simulation. The findings highlight the potential of these synthesized derivatives as effective antibacterial agents and provide valuable insights into their mechanism of action.

New mutation within a common haplotype is associated with calf muscle weakness in Holsteins

A recessive haplotype resulting in elevated calf mortality but with apparent incomplete penetrance was previously linked to the end of chromosome 16 (78.7-80.7 Mbp). Genotype analysis of 5.6 million Holsteins indicated that the haplotype was common and traced back to 1952, with a key ancestor born in 1984 (HOUSA1964484, Southwind) identified from chip genotypes as homozygous for the suspect haplotype. Sequence data from Southwind (an affected calf) and the sire of the affected calf were scanned for candidate mutations. A missense mutation with a deleterious projected impact at 79,613,592 bp was homozygous in the affected calf and heterozygous in the calf's sire and Southwind. Sequence data available from the Cooperative Dairy DNA Repository for 299 other Holsteins indicated a 97% concordance with the haplotype and an 89% call rate. The exon amino acid sequence appears to be broadly conserved in the CACNA1S gene, and mutations in humans and mice can cause phenotypes of temporary or permanent paralysis analogous to those in calves with the haplotype causing muscle weakness (HMW). Improved methods for using pedigree to track new mutations within existing haplotypes were developed and applied to the haplotypes for both muscle weakness and Holstein cholesterol deficiency (HCD). For HCD, concordance of the gene test with its haplotype status was greatly improved. For both defects, haplotype status was matched to heifer livability records for 558,000 calves. For HMW, only 46 heifers with livability records were homozygous and traced only to Southwind on both sides. Of those, 52% died before 18 mo at an average age of 1.7 ± 1.6 mo, but that death rate may be underestimated if only healthier calves were genotyped. The death rate was 2.4% for noncarriers. Different reporting methods or dominance effects may be needed to include HMW and other partially lethal effects in selection and mating. Direct tests are needed for new mutations within existing common haplotypes because tracking can be difficult even with accurate pedigrees when the original haplotype has a high frequency.

The mechanosensitive ion channel PIEZO1 promotes satellite cell function in muscle regeneration

Muscle satellite cells (MuSCs), myogenic stem cells in skeletal muscles, play an essential role in muscle regeneration. After skeletal muscle injury, quiescent MuSCs are activated to enter the cell cycle and proliferate, thereby initiating regeneration; however, the mechanisms that ensure successful MuSC division, including chromosome segregation, remain unclear. Here, we show that PIEZO1, a calcium ion (Ca²⁺)-permeable cation channel activated by membrane tension, mediates spontaneous Ca²⁺ influx to control the regenerative function of MuSCs. Our genetic engineering approach in mice revealed that PIEZO1 is functionally expressed in MuSCs and that Piezo1 deletion in these cells delays myofibre regeneration after injury. These results are, at least in part, due to a mitotic defect in MuSCs. Mechanistically, this phenotype is caused by impaired PIEZO1-Rho signalling during myogenesis. Thus, we provide the first concrete evidence that PIEZO1, a bona fide mechanosensitive ion channel, promotes proliferation and regenerative functions of MuSCs through precise control of cell division.

Selective Synthesis of the Aminobutadiene Intermediate and Mechanistic Analysis of 1,4-Dihydropyridine Formation Reaction in Water

We previously isolated an aminobutadiene derivative as a by-product in the synthesis of a 1,4-dihydropyridine (1,4-DHP) derivative by the reaction of methyl propiolate with excess ammonium acetate in water, and we proposed that it is an intermediate in the formation of 1,4-DHP. Here, to test this idea and to investigate the reaction mechanism, we selectively synthesized the aminobutadiene derivative in EtOH and examined its reactivity. The yield of the aminobutadiene derivative was increased in the presence of excess ammonium salt. X-Ray crystal structure analysis indicated the presence of an intramolecular hydrogen bond between the terminal amine and ester carbonyl oxygen, together with a short C-N bond length consistent with enamine-imine equilibrium. Direct cyclization of the aminobutadiene derivative with methyl propiolate to afford the 1,4-DHP derivative did not proceed well, but the yield was increased in the presence of morpholine salt as an additive. These results suggest that the predominant reaction pathway from the intermediate to 1,4-DHP in water involves Michael addition of a second amine molecule and reaction with methyl propiolate, followed by intramolecular cyclization and elimination of amine.

Molecular and cellular basis of genetically inherited skeletal muscle disorders

Neuromuscular disorders comprise a diverse group of human inborn diseases that arise from defects in the structure and/or function of the muscle tissue - encompassing the muscle cells (myofibres) themselves and their extracellular matrix - or muscle fibre innervation. Since the identification in 1987 of the first genetic lesion associated with a neuromuscular disorder - mutations in dystrophin as an underlying cause of Duchenne muscular dystrophy - the field has made tremendous progress in understanding the genetic basis of these diseases, with pathogenic variants in more than 500 genes now identified as underlying causes of neuromuscular disorders. The subset of neuromuscular disorders that affect skeletal muscle are referred to as myopathies or muscular dystrophies, and are due to variants in genes encoding muscle proteins. Many of these proteins provide structural stability to the myofibres or function in regulating sarcolemmal integrity, whereas others are involved in protein turnover, intracellular trafficking, calcium handling and electrical excitability - processes that ensure myofibre resistance to stress and their primary activity in muscle contraction. In this Review, we discuss how defects in muscle proteins give rise to muscle dysfunction, and ultimately to disease, with a focus on pathologies that are most common, best understood and that provide the most insight into muscle biology.

Mechanisms and Characteristics of Sulfonylureas and Glinides

BACKGROUND

Type 2 diabetes mellitus is a complex progressive endocrine disease characterized by hyperglycemia and life-threatening complications. It is the most common disorder of pancreatic cell function that causes insulin deficiency. Sulfonylurea is a class of oral hypoglycemic drugs. Over the past half century, these drugs, together with the subsequent non-sulfonylureas (glinides), have been the main oral drugs for insulin secretion.

OBJECTIVE

Through in-depth study, the medical profession considers it as an important drug for improving blood sugar control.

METHODS

The mechanism, characteristics, efficacy and side effects of sulfonylureas and glinides were reviewed in detail.

RESULTS

Sulfonylureas and glinides not only stimulated the release of insulin from pancreatic cells, but also had many extrapanular hypoglycemic effect, such as reducing the clearance rate of insulin in liver, reducing the secretion of glucagon, and enhancing the sensitivity of peripheral tissues to insulin in type 2 diabetes mellitus.

CONCLUSION

Sulfonylureas and glinides are effective first-line drugs for the treatment of diabetes mellitus. Although they have the risk of hypoglycemia, weight gain and cardiovascular disease, their clinical practicability and safety can be guaranteed as long as they are reasonably used.

Ca2+ influxes and transmembrane transport are essential for phytic acid degradation in mung bean sprouts

BACKGROUND

Phytic acid is considered as an antinutrient. Ca²⁺ addition during germination has been proved to be an effective method for reducing phytic acid content in seeds. In this study, mung bean sprouts were treated with LaCl₃ (La), verapamil (VP), ruthenium red (RR), and CaCl₂ to explore the effect of Ca²⁺ influxes on phytic acid degradation.

RESULTS

CaCl₂ (6 mmol L^-1 ) significantly improved extracellular and intracellular calcium precipitates and calcium content, elevated phytase and acid phosphatase activity, and further enhanced phytic acid degradation. Conversely, La, VP, or RR induced the opposite results. Among them, RR exhibited the most significant inhibitory effect. Decreased PA, PAP, MIPP, and ALP gene expression after VP or RR treatment was also observed. Enhanced or weakened extracellular Ca²⁺ influx or intracellular Ca²⁺ efflux was detected with increased or decreased calcium precipitates distributed in different compartments. However, CaCl₂ addition differentially reversed the inhibitory effects of all channel blockers.

CONCLUSION

CaCl₂ enhanced Ca²⁺ influxes and accumulation in cells, which contributed to the regulation of phytic acid degradation. This study demonstrates that calcium channels play an essential role in mediating phytic acid degradation in mung bean sprouts, and both extracellular and intracellular Ca²⁺ -regulation were involved in phytic acid degradation. © 2017 Society of Chemical Industry.

Periodic paralysis

The periodic paralyses are a group of skeletal muscle channelopathies characterizeed by intermittent attacks of muscle weakness often associated with altered serum potassium levels. The underlying genetic defects include mutations in genes encoding the skeletal muscle calcium channel Ca_v1.1, sodium channel Na_v1.4, and potassium channels K_ir2.1, K_ir3.4, and possibly K_ir2.6. Our increasing knowledge of how mutant channels affect muscle excitability has resulted in better understanding of many clinical phenomena which have been known for decades and sheds light on some of the factors that trigger attacks. Insights into the pathophysiology are also leading to new therapeutic approaches.

Voltage-gated calcium channels: Determinants of channel function and modulation by inorganic cations

Voltage-gated calcium channels (VGCCs) represent a key link between electrical signals and non-electrical processes, such as contraction, secretion and transcription. Evolved to achieve high rates of Ca(2+)-selective flux, they possess an elaborate mechanism for selection of Ca(2+) over foreign ions. It has been convincingly linked to competitive binding in the pore, but the fundamental question of how this is reconcilable with high rates of Ca(2+) transfer remains unanswered. By virtue of their similarity to Ca(2+), polyvalent cations can interfere with the function of VGCCs and have proven instrumental in probing the mechanisms underlying selective permeation. Recent emergence of crystallographic data on a set of Ca(2+)-selective model channels provides a structural framework for permeation in VGCCs, and warrants a reconsideration of their diverse modulation by polyvalent cations, which can be roughly separated into three general mechanisms: (I) long-range interactions with charged regions on the surface, affecting the local potential sensed by the channel or influencing voltage-sensor movement by repulsive forces (electrostatic effects), (II) short-range interactions with sites in the ion-conducting pathway, leading to physical obstruction of the channel (pore block), and in some cases (III) short-range interactions with extracellular binding sites, leading to non-electrostatic modifications of channel gating (allosteric effects). These effects, together with the underlying molecular modifications, provide valuable insights into the function of VGCCs, and have important physiological and pathophysiological implications. Allosteric suppression of some of the pore-forming Cavα1-subunits (Cav2.3, Cav3.2) by Zn(2+) and Cu(2+) may play a major role for the regulation of excitability by endogenous transition metal ions. The fact that these ions can often traverse VGCCs can contribute to the detrimental intracellular accumulation of metal ions following excessive release of endogenous Cu(2+) and Zn(2+) or exposure to non-physiological toxic metal ions.

Patch-clamp recording of voltage-sensitive Ca2+ channels

In this article, we focus on a refinement of the traditional voltage-clamp methods that are used to measure current from whole cells, or relatively large areas of membrane, called the patch-clamp technique. Although this technique has extended the application of voltage-clamp methods to the recording of ionic currents flowing through single channels, in its whole-cell configuration it has become the most widely used method for recording ionic currents. We give particular attention to the study of voltage-gated (CaV) Ca(2+) channels using the patch-clamp technique and discuss some aspects of the molecular physiology of these proteins.

The interaction between mGluR1 and the calcium channel Cav₂.₁ preserves coupling in the presence of long Homer proteins

Group I metabotropic glutamate receptors (mGluR1 and 5) are G protein coupled receptors that regulate neuronal activity in a number of ways. Some of the most well studied functions of group I mGluRs, such as initiation of multiple forms of mGluR-dependent long-term depression, require receptor localization near the post-synaptic density (PSD). This localization is in turn dependent on the Homer family of scaffolding proteins which bind to a small motif on the distal C-termini of mGluR1 and 5, localize the receptors near the PSD, strengthen coupling to post-synaptic effectors and simultaneously uncouple the mGluRs from extra-synaptic effectors such as voltage dependent ion channels. Here the selectivity of this uncoupling process was examined by testing the ability of Homer-2b to uncouple mGluR1 from multiple voltage dependent calcium channels including Ca(V2.2) (N-type), Ca(V3.2) (T-type), and Ca(V2.1) (P/Q-type) expressed in rat sympathetic neurons from the superior cervical ganglion (SCG). Of these, only the mGluR1-Ca(V2.1) modulatory pathway was insensitive to Homer-2b expression. Uncoupling from this channel was achieved by co-expression of an mGluR1 C-terminal protein designed to disrupt a previously described direct interaction between these two proteins, suggesting that this interaction allows incorporation of Ca(V2.1) into the mGluR1/Homer signaling complex, thereby preserving modulation in the presence of scaffolding Homer proteins. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Reciprocal dihydropyridine and ryanodine receptor interactions in skeletal muscle activation

Dihydropyridine (DHPR) and ryanodine receptors (RyRs) are central to transduction of transverse (T) tubular membrane depolarisation initiated by surface action potentials into release of sarcoplasmic reticular (SR) Ca2+ in skeletal muscle excitation-contraction coupling. Electronmicroscopic methods demonstrate an orderly positioning of such tubular DHPRs relative to RyRs in the SR at triad junctions where their membranes come into close proximity. Biochemical and genetic studies associated expression of specific, DHPR and RyR, isoforms with the particular excitation-contraction coupling processes and related elementary Ca2+ release events found respectively in skeletal and cardiac muscle. Physiological studies of intramembrane charge movements potentially related to voltage triggering of Ca2+ release demonstrated a particular qγ charging species identifiable with DHPRs through its T-tubular localization, pharmacological properties, and steep voltage-dependence paralleling Ca2+ release. Its nonlinear kinetics implicated highly co-operative conformational events in its transitions in response to voltage change. The effects of DHPR and RyR agonists and antagonists upon this intramembrane charge in turn implicated reciprocal rather than merely unidirectional DHPR-RyR interactions in these complex reactions. Thus, following membrane potential depolarization, an orthograde qγ-DHPR-RyR signaling likely initiates conformational alterations in the RyR with which it makes contact. The latter changes could then retrogradely promote further qγ-DHPR transitions through reciprocal co-operative allosteric interactions between receptors. These would relieve the resting constraints on both further, delayed, nonlinear qγ-DHPR charge transfers and on RyR-mediated Ca2+ release. They would also explain the more rapid charging and recovery qγ transients following larger depolarizations and membrane potential repolarization to the resting level.

Engineering proteins for custom inhibition of Ca(V) channels

The influx of Ca(2+) ions through voltage-dependent calcium (Ca(V)) channels links electrical signals to physiological responses in all excitable cells. Not surprisingly, blocking Ca(V) channel activity is a powerful method to regulate the function of excitable cells, and this is exploited for both physiological and therapeutic benefit. Nevertheless, the full potential for Ca(V) channel inhibition is not being realized by currently available small-molecule blockers or second-messenger modulators due to limitations in targeting them either to defined groups of cells in an organism or to distinct subcellular regions within a single cell. Here, we review early efforts to engineer protein molecule blockers of Ca(V) channels to fill this crucial niche. This technology would greatly expand the toolbox available to physiologists studying the biology of excitable cells at the cellular and systems level.

Forward genetic screen of mouse reveals dominant missense mutation in the P/Q-type voltage-dependent calcium channel, CACNA1A

Dominant mutations of the P/Q-type Ca(2+) channel (CACNA1A) underlie several human neurological disorders, including episodic ataxia type 2, familial hemiplegic migraine 1 (FHM1) and spinocerebellar ataxia 6, but have not been found previously in the mouse. Here we report the first dominant ataxic mouse model of Cacna1a mutation. This Wobbly mutant allele of Cacna1a was identified in an ethylnitrosourea (ENU) mutagenesis dominant behavioral screen. Heterozygotes exhibit ataxia from 3 weeks of age and have a normal life span. Homozygotes have a righting reflex defect from postnatal day 8 and later develop severe ataxia and die prematurely. Both heterozygotes and homozygotes exhibit cerebellar atrophy with focal reduction of the molecular layer. No obvious loss of Purkinje cells or decrease in size of the granule cell layer was observed. Real-time polymerase chain reaction revealed altered expression levels of Cacna1g, Calb2 and Th in Wobbly cerebella, but Cacna1a messenger RNA and protein levels were unchanged. Positional cloning revealed that Wobbly mice have a missense mutation leading to an arginine to leucine (R1255L) substitution, resulting in neutralization of a positively charged amino acid in repeat III of voltage sensor segment S4. The dominance of the Wobbly mutation more closely resembles patterns of CACNA1A mutation in humans than previously described mouse recessive mutants (tottering, leaner, rolling Nagoya and rocker). Positive-charge neutralization in S4 has also been shown to underlie several cases of human dominant FHM1 with ataxia. The Wobbly mutant thus highlights the importance of the voltage sensor and provides a starting point to unravel the neuropathological mechanisms of this disease.

The sequence of events that underlie quantal transmission at central glutamatergic synapses

The properties of synaptic transmission were first elucidated at the neuromuscular junction. More recent work has examined transmission at synapses within the brain. Here we review the remarkable progress in understanding the biophysical and molecular basis of the sequential steps in this process. These steps include the elevation of Ca2+ in microdomains of the presynaptic terminal, the diffusion of transmitter through the fusion pore into the synaptic cleft and the activation of postsynaptic receptors. The results give insight into the factors that control the precision of quantal transmission and provide a framework for understanding synaptic plasticity.

Insulin-like growth factors (IGF) I and II utilize different calcium signaling pathways in a primary human parathyroid cell culture model

BACKGROUND

In most cell types, influx of calcium (Ca2+) induces a growth or secretory response. The opposite occurs in parathyroid (PTH), cells where there is an inverse relationship between intracellular Ca2+ concentration and PTH secretion. We have examined the effects of calcium channel and metabolism modulators on insulin-like growth factors (IGFs) in a parathyroid cell culture model.

METHODS

Cell cultures were prepared from 9 patients undergoing operation for hyperparathyroidism. Following adhesion, the cells were transferred to serum-free medium and dosed with IGF I, II +/- ethyleneglycol-bis(beta-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), nifedipine, nickel, 2-aminoethoxy-diphenylborate (2-APB), or dantrolene. Proliferation (96 hours) was assessed by measuring tritiated thymidine incorporation and PTH release (1 and 3 hours) assayed by IRMA.

RESULTS

Both IGF I and II increased DNA synthesis to 162.8% +/- 10.6% (SEM) and 131.1% +/- 7.7%, respectively (P < 0.05). EGTA at 0.2 mmol (ionized Ca2+ 0.2 mmol) did not affect the response to both IGFs. EGTA at 2 mmol (ionized Ca2+ 0 mmol) reduced the DNA synthesis of IGF I and II to 29% and 26%, respectively (P < 0.05). Nifedipine and nickel (nonspecific Ca2+ channel blocker) were equally potent in negating the mitogenic effects of both IGFs. 2-APB (IP3R blocker) reduced the basal DNA synthesis to 51.3% +/- 8.4% but had no effect on either IGF. Dantrolene (ryanodine receptor blocker) negated IGF II induced mitogenisis (74.2% +/- 6.7%) and partially inhibited IGF I mitogenesis (123% +/- 6%) (P < 0.05). The rate of PTH secretion was greater after IGF II stimulation than after IGF I stimulation.

CONCLUSIONS

IGFs I and II induce mitogenesis by different calcium signaling pathways. These data suggest that parathyroid cells may utilize different calcium signaling pathways to distinguish growth factors and serum calcium changes.

Human immunodeficiency virus type 1 Tat protein induces an intracellular calcium increase in human monocytes that requires DHP receptors: involvement in TNF-alpha production

HIV-1 Tat protein, acting at the cell membrane, stimulates the production by human monocytes of TNF-alpha, a cytokine implicated in both HIV-1 replication and pathogenesis. Here, we analyze, in primary human monocytes, the mechanisms involved in Tat-stimulated calcium mobilization and its relationship with TNF-alpha production. We show that the Tat protein induces a calcium signal by mobilizing calcium from extracellular stores. This calcium signal is totally blocked when cells are stimulated in the presence of DHP receptor inhibitors such as nimodipine or calcicludine, thus suggesting the implication of this L-type calcium channel. By using RT-PCR amplification, Western blot with antibodies directed against the alpha1D subunit, binding assays with specific agonists or antagonists, and inhibition with specific antisense oligonucleotides, we show that DHP receptors are expressed and functional in primary human monocytes. Interestingly, we demonstrate that Tat-induced calcium mobilization is tightly linked to TNF-alpha production, thus indicating that Tat-induced mobilization and TNF-alpha production are entirely mediated by DHP receptors, as shown by their total inhibition by nimodipine, calcicludine, or anti-alpha1D antisense oligonucleotides.

Mapping sites of potential proximity between the dihydropyridine receptor and RyR1 in muscle using a cyan fluorescent protein-yellow fluorescent protein tandem as a fluorescence resonance energy transfer probe

Excitation-contraction coupling in skeletal muscle involves conformational coupling between the dihydropyridine receptor (DHPR) and the type 1 ryanodine receptor (RyR1) at junctions between the plasma membrane and sarcoplasmic reticulum. In an attempt to find which regions of these proteins are in close proximity to one another, we have constructed a tandem of cyan and yellow fluorescent proteins (CFP and YFP, respectively) linked by a 23-residue spacer, and measured the fluorescence resonance energy transfer (FRET) of the tandem either in free solution or after attachment to sites of the alpha1S and beta1a subunits of the DHPR. For all of the sites examined, attachment of the CFP-YFP tandem did not impair function of the DHPR as a Ca2+ channel or voltage sensor for excitation-contraction coupling. The free tandem displayed a 27.5% FRET efficiency, which decreased significantly after attachment to the DHPR subunits. At several sites examined for both alpha1S (N-terminal, proximal II-III loop of a two fragment construct) and beta1a (C-terminal), the FRET efficiency was similar after expression in either dysgenic (alpha1S-null) or dyspedic (RyR1-null) myotubes. However, compared with dysgenic myotubes, the FRET efficiency in dyspedic myotubes increased from 9.9 to 16.7% for CFP-YFP attached to the N-terminal of beta1a, and from 9.5 to 16.8% for CFP-YFP at the C-terminal of alpha1S. Thus, the tandem reporter suggests that the C terminus of alpha1S and the N terminus of beta1a may be in close proximity to the ryanodine receptor.

Calcium entry through L-type calcium channels is essential for neurite regeneration in cultured sympathetic neurons

Previous work showed that a post-neuritotomy rise in [Ca2+]i is required for regeneration. We tested the following hypotheses in cultured sympathetic neurons: (1) blocking L-type channels at the time of injury inhibits regeneration; (2) enhancing Ca2+ entry through L-type Ca2+ channels enhances regeneration; (3) L-type Ca2+ channel distribution is predominantly on the soma and proximal neurites of uninjured and injured neurons. To visualize L-type Ca2+ channels and block Ca2+ influx, the fluorescent dihydropyridine antagonist, DM-BODIPY, was used. Our results show that regeneration is markedly inhibited by the antagonist when administered 20 min. prior to injury, in the presence or absence of nerve growth factor (NGF) (p < 0.0001). Severe degeneration of proximal and distal neurites was seen 48 h after injury. Regeneration was minimally inhibited by the antagonist when administered 5 min after injury (p < 0.05), but not inhibited when administered 2 or 24 h after injury (p > 0.05). We found that L-type channels are distributed ubiquitously on the soma and neurites of uninjured and injured cells, and on regenerating neurites. The addition of the L-type channel agonist, BayK8644, (1 microM) 20 min prior to injury enhanced neurite length at 24 h post-injury (p = 0.002). Blocking L-type channels did not affect the viability of uninjured or injured cells. For the first time, it has been shown that Ca2+ entry through L-type Ca2+ channels is essential for post-neuritotomy sympathetic neurite regeneration, and that this effect shows a strict temporal dependency. We also demonstrated that regeneration can be enhanced by increasing Ca2+ influx through L-type channels.

Gamma 1 subunit interactions within the skeletal muscle L-type voltage-gated calcium channels

Voltage-gated calcium channels mediate excitationcontraction coupling in the skeletal muscle. Their molecular composition, similar to neuronal channels, includes the pore-forming alpha(1) and auxiliary alpha(2)delta, beta, and gamma subunits. The gamma subunits are the least characterized, and their subunit interactions are unclear. The physiological importance of the neuronal gamma is emphasized by epileptic stargazer mice that lack gamma(2). In this study, we examined the molecular basis of interaction between skeletal gamma(1) and the calcium channel. Our data show that the alpha(1)1.1, beta(1a), and alpha(2)delta subunits are still associated in gamma(1) null mice. Reexpression of gamma(1) and gamma(2) showed that gamma(1), but not gamma(2), incorporates into gamma(1) null channels. By using chimeric constructs, we demonstrate that the first half of the gamma(1) subunit, including the first two transmembrane domains, is important for subunit interaction. Interestingly, this chimera also restores calcium conductance in gamma(1) null myotubes, indicating that the domain mediates both subunit interaction and current modulation. To determine the subunit of the channel that interacts with gamma(1), we examined the channel in muscular dysgenesis mice. Cosedimentation experiments showed that gamma(1) and alpha(2)delta are not associated. Moreover, alpha(1)1.1 and gamma(1) subunits form a complex in transiently transfected cells, indicating direct interaction between the gamma(1) and alpha(1)1.1 subunits. Our data demonstrate that the first half of gamma(1) subunit is required for association with the channel through alpha(1)1.1. Because subunit interactions are conserved, these studies have broad implications for gamma heterogeneity, function and subunit association with voltage-gated calcium channels.

Structure of the voltage-gated L-type Ca2+ channel by electron cryomicroscopy

Voltage-dependent L-type Ca(2+) channels play important functional roles in many excitable cells. We present a three-dimensional structure of an L-type Ca(2+) channel. Electron cryomicroscopy in conjunction with single-particle processing was used to determine a 30-A resolution structure of the channel protein. The asymmetrical channel structure consists of two major regions: a heart-shaped region connected at its widest end with a handle-shaped region. A molecular model is proposed for the arrangement of this skeletal muscle L-type Ca(2+) channel structure with respect to the sarcoplasmic reticulum Ca(2+)-release channel, the physical partner of the L-type channel for signal transduction during the excitation-contraction coupling in muscle.

Inhibitory effects of 1,4-DHP antagonists on synaptic GABA release modulated by BAY-K 8644 in mechanically dissociated rat substantia innominata

The effects of dihydropyridine (1,4-DHP) agonist and antagonists on miniature inhibitory postsynaptic currents (mIPSCs) were investigated in mechanically dissociated rat substantia innominata neurons attached to native GABAergic presynaptic nerve terminals, namely 'synaptic bouton preparation', using nystatin perforated patch recording mode under voltage-clamp conditions. BAY-K 8644 (BAY-K), an L-type Ca(2+) channel agonist, reversibly and concentration dependently facilitated the GABAergic mIPSC frequency without altering the distribution of current amplitudes. Removal of extracellular Ca(2+) completely suppressed the facilitatory effect of BAY-K on mIPSC frequency. The facilitatory effect of BAY-K on mIPSC frequency was maintained even in the presence of selective N-, P- and Q-type Ca(2+) channel antagonists, such as 3 x 10(-6) M omega-conotoxin-GVIA (omega-CgTX-GVIA), 3 x 10(-8) M omega-agatoxin-IVA (omega-AgTX-IVA) and 3 x 10(-6)M omega-conotoxin-MVIIC (omega-CmTX-MVIIC). However, nicardipine (3 x 10(-6) M) and nimodipine (3 x 10(-6) M), 1,4-DHP antagonists, significantly inhibited the mIPSC frequency enhanced by BAY-K by 37 +/- 5 and 42 +/- 6%, respectively. These results suggest the possible existence of L-type Ca(2+) channels in GABAergic presynaptic nerve terminals.

Developmental expression patterns of alpha1H T-type Ca2+ channels during spermatogenesis and organogenesis in mice

The objectives of the present study were to investigate the expression patterns of T-type Ca2+ channel mRNA during spermatogenesis and organogenesis in mice. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to identify the subtypes of calcium channels present in the round spermatids isolated from mouse testes by flow cytometry. Transcripts of L-type (alpha1D), non-L-type (alpha1E) and T-type Ca2+ channels were detected in round spermatids. Analysis of PCR products of T-type Ca2+ channels indicated that only alpha1H subunits were detected in round spermatids. The appearance and differential distribution of alpha1H T-type Ca2+ channel mRNA during mouse spermatogenesis and postimplantation embryogenesis (embryonic (E) days E9, E12, E15) were investigated by in situ hybridization with digoxigenin-labeled RNA probes coupled with alkaline phosphatase detection. In testes from adult and immature mice (postnatal 2 and 3 weeks), alpha1H T-type Ca2+ channel mRNA was expressed in all developing germ cells and sertoli cells. On E9 and E12, tissues of the central nervous system, such as the telencephalon, expressed alpha1H T-type Ca2+ channel mRNA. On E15, signals were detected throughout all organs of the embryo. These findings indicate that the expression of alpha1H T-type Ca2+ channels is spatio-temporally regulated during spermatogenesis and organogenesis.

Preassociation of calmodulin with voltage-gated Ca(2+) channels revealed by FRET in single living cells

Among the most intriguing forms of Ca(2+) channel modulation is the regulation of L-type and P/Q-type channels by intracellular Ca(2+), acting via unconventional channel-calmodulin (CaM) interactions. In particular, overexpressing Ca(2+)-insensitive mutant CaM abolishes Ca(2+)-dependent modulation, hinting that Ca(2+)-free CaM may "preassociate" with these channels to enhance detection of local Ca(2+). Despite the far-reaching consequences of this proposal, in vitro experiments testing for preassociation provide conflicting results. Here, we develop a three filter-cube fluorescence resonance energy transfer method (three-cube FRET) to directly probe for constitutive associations between channel subunits and CaM in single living cells. This FRET assay detects Ca(2+)-independent associations between CaM and the pore-forming alpha(1) subunit of L-type, P/Q-type, and, surprisingly, R-type channels. These results now definitively demonstrate channel-CaM preassociation in resting cells and underscore the potential of three-cube FRET for probing protein-protein interactions.

Time- and subunit-dependent differential mRNA expression of L-type Ca2+ channel during progression of right ventricular hypertrophy

To clarify the molecular basis for changes in L-type calcium channel (VLCC) density in ventricular hypertrophy, we analyzed the mRNA expression of all the subunits including the main subunit alpha1c and auxiliary subunits (alpha2delta, beta2 and beta3) composing VLCC in rat right ventricular hypertrophy (RVH) induced by monocrotaline injection. To test the hypothesis that the expression of each subunit might change differently during progression of RVH, leading to an altered electrophysiologic outcome for VLCC, we investigated the ratio of the mRNA level of each auxiliary subunit to the main subunit. After monocrotaline injection, alpha1c mRNA showed a transient decrease on the 14th day and thereafter significantly increased to reach approximately 1.8 fold that of the control level on the 21st day. The auxiliary subunit alpha2delta mRNA showed a pattern similar to that of alpha1c. The beta3 mRNA increased rapidly after monocrotaline injection and increased approximately 4.1 fold. On the other hand, beta2 mRNA showed no significant changes. Accordingly, only the mRNA ratio of beta3 to alpha1c showed a significant increase among the auxiliary subunits after the monocrotaline injection. The ratio increased to a maximum of approximately 5.7 fold on the 14th day and thereafter decreased. These results suggest that VLCC density may be modified not only by alpha1c but also by its auxiliary subunit expression in ventricular hypertrophy, and provide a clue for understanding the controversial electrophysiologic results on VLCC density in hypertrophied hearts.

Reduced voltage sensitivity of activation of P/Q-type Ca2+ channels is associated with the ataxic mouse mutation rolling Nagoya (tg(rol))

Recent genetic analyses have revealed an important association of the gene encoding the P/Q-type voltage-dependent Ca(2+) channel alpha(1A) subunit with hereditary neurological disorders. We have identified the ataxic mouse mutation, rolling Nagoya (tg(rol)), in the alpha(1A) gene that leads to a charge-neutralizing arginine-to-glycine substitution at position 1262 in the voltage sensor-forming segment S4 in repeat III. Ca(2+) channel currents in acutely dissociated Purkinje cells, where P-type is the dominant type, showed a marked decrease in slope and a depolarizing shift by 8 mV of the conductance-voltage curve and reduction in current density in tg(rol) mouse cerebella, compared with those in wild-type. Compatible functional change was induced by the tg(rol) mutation in the recombinant alpha(1A) channel, indicating that a defect in voltage sensor of P/Q-type Ca(2+) channels is the direct consequence of the tg(rol) mutation. Furthermore, somatic whole-cell recording of mutant Purkinje cells displayed only abortive Na(+) burst activity and hardly exhibited Ca(2+) spike activity in cerebellar slices. Thus, in tg(rol) mice, reduced voltage sensitivity, which may derive from a gating charge defect, and diminished activity of the P-type alpha(1A) Ca(2+) channel significantly impair integrative properties of Purkinje neurons, presumably resulting in locomotor deficits.

L-type calcium channels in the hippocampus and cerebellum of Alzheimer's disease brain tissue

There is growing evidence that the selective neuronal cell death observed in Alzheimer's Disease (AD) is the result of dysregulation of intracellular calcium (Ca2+) homeostasis. In the present study, L-type voltage sensitive calcium channels (L-VSCCs) were examined in the cerebellum and hippocampus of AD (n = 6; postmortem interval less than 5 h) and age-matched control (n = 6) tissue by homogenate binding techniques and quantitative in vitro receptor autoradiography using [3H]isradipine (PN200-110). Saturation analyses of the cerebellum revealed unaltered [3H]isradipine binding parameters (Kd and Bmax) between AD and control subjects. Analysis of AD and control hippocampus demonstrated significant differences as [3H]isradipine binding increased (62%) in AD, whereas hippocampal cell density decreased (29%) in AD, relative to control subjects. Moreover, AD differentially affected L-VSCC in area CA1 and dentate gyrus. The dentate gyrus had greatly increased binding (77%) with little cell loss (16%) in AD brains, whereas area CA1 had increased binding (40%) with significant cell loss (42%) in AD brains, relative to controls. The results of the present study suggest that hippocampal area CA1 may experience greater cell loss in response to increased L-VSCCs in AD relative to other brain regions.

Voltage-gated T-type Ca2+ channels and heart failure

In the cardiovascular system, two types of voltage-gated Ca2+ channels are present: the L-type and the T-type. Under normal conditions, T-type Ca2+ channels are involved in the maintenance of vascular tone and cardiac automaticity but, since they are not present in contractile myocardial cells, they do not contribute significantly to myocardial contraction. In experimental models of cardiac hypertrophy, myocardial T-type Ca2+ channels are upregulated, which could contribute to the increased incidence of ventricular arrhythmia. In addition, T-type Ca2+ channels participate in the regulation of cell proliferation and neurohormonal secretion; through these pathways, T-type Ca2+ channels might participate in myocardial remodeling. The pathophysiological role of T-type Ca2+ channels in heart failure has been investigated using mibefradil, a Ca2+ antagonist that is 10-50 times more potent at blocking T-type than L-type Ca2+ channels. In contrast with classic L-type Ca2+ channel antagonists, miberfradil appears beneficial in many animal models of heart failure; in particular, it does not exert negative inotropic effects nor does it stimulate the neurohormonal system. Furthermore, in the Pfeffer rat model, blockade of T-type Ca2+ channels with mibefradil is associated with an improved survival rate. In humans, however, major metabolic drug interactions independent of T-type Ca2+ channel blockade made it impossible to determine the efficacy of mibefradil in treating heart failure; indeed, these interactions led to the withdrawal of the drug from the market.

Auxiliary subunits operate as a molecular switch in determining gating behaviour of the unitary N-type Ca2+ channel current in Xenopus oocytes

1. We systematically examined the biophysical properties of omega-conotoxin GVIA-sensitive neuronal N-type channels composed of various combinations of the alpha1B, alpha2/delta and beta1b subunits in Xenopus oocytes. 2. Whole-cell recordings demonstrated that coexpression of the beta1b subunit decelerated inactivation, whereas the alpha2/delta accelerated both activation and inactivation, and cancelled the kinetic effects of the beta1b. The alpha2/delta and the beta1b controlled voltage dependence of activation differently: the beta1b significantly shifted the current-voltage relationship towards the hyperpolarizing direction; however, the alpha2/delta shifted the relationship only slightly in the depolarizing direction. The extent of voltage-dependent inactivation was modified solely by the beta1b. 3. Unitary currents measured using a cell-attached patch showed stable patterns of opening that were markedly different among subunit combinations in their kinetic parameters. The alpha2/delta and the beta1b subunits also acted antagonistically in regulating gating patterns of unitary N-type channels. Open time was shortened by the alpha2/delta, while the fraction of long opening was enhanced by the beta1b. The alpha2/delta decreased opening probability (Po), while the beta1b increased Po. alpha1Balpha2/deltabeta1b produced unitary activity with an open time distribution value in between those of alpha1Balpha2/delta and alpha1Bbeta1b. However, both the alpha2/delta and the beta1b subunits reduced the number of null traces. 4. These results suggest that the auxiliary subunits alone and in combination contribute differently in forming gating apparatuses in the N-type channel, raising the possibility that subunit interaction contributes to the generation of functional diversity of N-type channels in native neuronal preparations also.

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.

Class differences in the effects of calcium channel blockers in the rat remnant kidney model

BACKGROUND

Controversy persists as to the existence of class differences between calcium channel blockers (CCBs) in their ability to provide renoprotection and as to potential mechanisms involved.

METHODS

Rats with 5/6 renal ablation were left untreated or received diltiazem, verapamil, or felodipine after the first week, and the relationship between continuous radiotelemetrically measured blood pressure (BP) and glomerulosclerosis (GS) was assessed at seven weeks. Additionally, the effects of these CCBs on renal autoregulation and hypertrophy were examined at three weeks after renal ablation.

RESULTS

Although an excellent linear correlation was observed between the average BP levels and GS in all groups (r = 0.75 to 0.84, P < 0.01), significant protection was not achieved with any of the CCBs, but for different reasons. The antihypertensive effects of diltiazem were not sustained beyond the second week. Verapamil significantly reduced the average BP (144 +/- 4 mm Hg vs. 181 +/- 8 in untreated rats) but shifted the slope of the relationship between BP and GS (increase in percentage GS/mm Hg increase in average systolic BP) to the left (x intercept 121 vs. 144 mm Hg for untreated rats, P < 0.01) so that GS was not reduced. Felodipine also significantly reduced the average BP (144 +/- 3 mm Hg) and shifted the slope to the left (x intercept 123 mm Hg), but additionally made the slope steeper (2.3 +/- 0.5 vs. 0.82 +/- 0.2 in untreated rats). Because of these differing effects on the relationship between BP and GS, the rank order of GS for any given BP elevation was as follows: felodipine > verapamil > diltiazem = untreated. Felodipine, but not verapamil or diltiazem, caused additional impairment of the already impaired renal autoregulation in untreated rats, thereby explaining its adverse effects on GS. By contrast, the adverse effects of verapamil on GS were attributable to the greater amplitude of BP fluctuations that was observed in the verapamil-treated rats such that for any given average BP, these rats were exposed to greater peak pressures as compared with the other groups. None of the CCBs had a significant effect on glomerular hypertrophy.

CONCLUSIONS

These class differences between CCBs in their relative impact on systemic BP profiles, renal autoregulation, and glomerular pressure transmission may have clinically significant implications and may account for the variable glomeruloprotection that has been observed with these agents in both experimental models and in humans.

Neuronal voltage-activated calcium channels: on the roles of the alpha 1E and beta 3 subunits

Many neurons of the central and peripheral nervous systems display multiple high voltage-activated (HVA) Ca2+ currents, often classified as L-, N-, P-, Q, and R-type. The heterogeneous properties of these channels have been attributed to diversity in their pore-forming alpha 1, subunits, in association with various beta subunits. However, there are large gaps in understanding how individual subunits contribute to Ca2+ channel diversity. Here we describe experiments to investigate the roles of alpha 1E and beta 3 subunits in mammalian neurons. The alpha 1E subunit is the leading candidate to account for the R-type channel, the least understood of the various types of high voltage-activated Ca2+ channels. Incubation with alpha 1E antisense oligonucleotide caused a 53% decrease in the peak R-type current density, while no significant changes in the current expression were seen in sense oligonucleotide-treated cells. The specificity of the alpha 1E antisense oligonucleotides was supported by the lack of change in the amplitude of P/Q current. These results upheld the hypothesis that members of the E class of alpha 1 subunits support the high voltage-activated R-type current in cerebellar granule cells. We studied the role of the Ca2+ channel beta 3 subunit using a gene targeting strategy. In sympathetic beta 3-/- neurons, the L-type current was significantly reduced relative to wild type (wt). In addition, N-type Ca2+ channels made up a smaller proportion of the total Ca2+ current than in wt due to a lower N-type current density in a group of neurons with small total currents. Voltage-dependent activation of P/Q-type Ca2+ channels was described by two Boltzmann components with different voltage dependence. The absence of the beta 3 subunit was associated with a shift in the more depolarized component of the activation along the voltage axis toward more negative potentials. The overall conclusion is that deletion of the beta 3 subunit affects at least three distinct types of HVA Ca2+ channel, but no single type of channel is solely dependent on beta 3.

Single tottering mutations responsible for the neuropathic phenotype of the P-type calcium channel

Recent genetic and molecular biological analyses have revealed many forms of inherited channelopathies. Homozygous ataxic mice, tottering (tg) and leaner (tgla) mice, have mutations in the P/Q-type Ca2+ channel alpha1A subunit gene. Although their clinical phenotypes, histological changes, and locations of gene mutations are known, it remains unclear what phenotypes the mutant Ca2+ channels manifest, or whether the altered channel properties are the primary consequence of the mutations. To address these questions, we have characterized the electrophysiological properties of Ca2+ channels in cerebellar Purkinje cells, where the P-type is the dominant Ca2+ channel, dissociated from the normal, tg, and tgla mice, and compared them with the properties of the wild-type and mutant alpha1A channels recombinantly expressed with the alpha2 and beta subunits in baby hamster kidney cells. The most striking feature of Ca2+ channel currents of mutant Purkinje cells was a marked reduction in current density, being reduced to approximately 60 and approximately 40% of control in tg and tgla mice, respectively, without changes of cell size. The Ca2+ channel currents in the tg Purkinje cells showed a relative increase in non-inactivating component in voltage-dependent inactivation. Besides the same change, those of the tgla mice showed a more distinct change in voltage dependence of activation and inactivation, being shifted in the depolarizing direction by approximately 10 mV, with a broader voltage dependence of inactivation. In the recombinant expression system, the tg channel with a missense mutation (P601L) and one form of the two possible tgla aberrant splicing products, tgla (short) channel, showed a significant reduction in current density, while the other form of the tgla channels, tgla (long), had a current density comparable to the normal control. On the other hand, the shift in voltage dependence of activation and inactivation was observed only for the tgla (long) channel. Comparison of properties of the native and recombinant mutant channels suggests that single tottering mutations are directly responsible for the neuropathic phenotypes of reduction in current density and deviations in gating behavior, which lead to neuronal death and cerebellar atrophy.

Antisense oligonucleotides against alpha1E reduce R-type calcium currents in cerebellar granule cells

Many neurons of the central nervous system display multiple high voltage-activated Ca2+ currents, pharmacologically classified as L-, N-, P-, Q-, and R-type. Of these current types, the R-type is the least understood. The leading candidate for the molecular correlate of R-type currents in cerebellar granule cells is the alpha1E subunit, which yields Ca2+ currents very similar to the R-type when expressed in heterologous systems. As a complementary approach, we tested whether antisense oligonucleotides against alpha1E could decrease the expression of R-type current in rat cerebellar granule neurons in culture. Cells were supplemented with either antisense or sense oligonucleotides and whole-cell patch clamp recordings were obtained after 6-8 days in vitro. Incubation with alpha1E antisense oligonucleotide caused a 52.5% decrease in the peak R-type current density, from -10 +/- 0.6 picoamperes/picofarad (pA/pF) (n = 6) in the untreated controls to -4.8 +/- 0.8 pA/pF (n = 11) (P < 0.01). In contrast, no significant changes in the current expression were seen in sense oligonucleotide-treated cells (-11.3 +/- 3.2 pA/pF). The specificity of the alpha1E antisense oligonucleotides was supported by the lack of change in estimates of the P/Q current amplitude. Furthermore, antisense and sense oligonucleotides against alpha1A did not affect R-type current expression (-11.5 +/- 1.7 and -11.7 +/- 1.7 pA/pF, respectively), whereas the alpha1A antisense oligonucleotide significantly reduced whole cell currents under conditions in which P/Q current is dominant. Our results support the hypothesis that members of the E class of alpha1 subunits support the high voltage-activated R-type current in cerebellar granule cells.

Changes in L-type calcium channel abundance and function during the transition to pacing-induced congestive heart failure

OBJECTIVE

The development of congestive heart failure (CHF) is accompanied by left ventricular (LV) and myocyte contractile dysfunction. However, time-dependent cellular and ionic events which contribute to the initiation and progression of CHF remain unclear. This study tested the central hypothesis that changes in L-type Ca2+ channel current (ICa) and abundance (Bmax) are early events in the transition to CHF.

METHODS

LV fractional shortening by echocardiography, isolated LV myocyte shortening velocity by videomicroscopy, ICa by voltage-clamp, and Bmax by [3H]nitrendipine binding were determined at each week during the progression of pacing-induced CHF in pigs (240 bpm; n = 6/week for 3 weeks). Myocyte and L-type Ca2+ channel function were determined under basal conditions and after beta-adrenergic receptor stimulation with 25 nM isoproterenol.

RESULTS

After 1 week of pacing, myocyte and L-type Ca2+ current responses to beta-adrenergic receptor stimulation were reduced by 20% from control values and was accompanied by over a 210% increase in plasma catecholamine levels. After 2 weeks of pacing, reductions in LV fractional shortening and myocyte shortening velocity from control values (20 +/- 1 vs. 34 +/- 2% and 36.7 +/- 2.9 vs. 50.6 +/- 2.4 microns/s, respectively, P < 0.05) were paralleled by decreased ICa (2.47 +/- 0.10 vs. 3.63 +/- 0.25 pA/pF, P < 0.02) and Bmax (149 +/- 16 vs. 180 +/- 12 fmol/mg, P < 0.03). After 3 weeks of pacing, LV fractional shortening was reduced by over 50%, myocyte shortening velocity by 37%, and ICa and Bmax were reduced by over 25% from control values. Furthermore, after 3 weeks of pacing, the ICa/Bmax ratio was reduced from control values (16.2 +/- 0.9 vs. 20.6 +/- 1.2 [fA/pF]/[fmol/mg], P < 0.03), which suggests functional defects in the remaining L-type Ca2+ channels.

CONCLUSIONS

An early event during the transition to pacing-induced CHF was diminished beta-adrenergic receptor augmented L-type Ca2+ current, which was followed by an absolute loss of steady-state L-type Ca2+ current and channel abundance. The development of severe CHF was accompanied by a loss of Ca2+ carrying capacity through residual channels. These unique findings suggest that a contributory molecular mechanism for the initiation and progression of CHF is changes in the structure and function of the L-type Ca2+ channels.

Reduced sarcolemmal dystrophin distribution and upregulation of utrophin in the cardiac and skeletal muscles of CHF-146 dystrophic hamsters

Abnormalities in the dystrophic gene product, dystrophin, have been implicated in initiating the primary membrane defect and excessive intracellular calcium accumulation (EICA), which play fundamental pathogenic roles in hereditary muscular dystrophy (HMD). Two other cytoskeletal proteins, spectrin and utrophin, bear remarkable structural and functional homologies to dystrophin. CHF-146 strain dystrophic hamsters (DH), like patients with Duchenne muscular dystrophy (DMD), die prematurely from cardiopulmonary insufficiency, focal myonecrosis, and progressive degeneration of the cardiac and skeletal muscles with EICA. Although DH present a suitable model for HMD, there are controversies concerning their dystrophin and utrophin status. Using immunocytochemistry and Western blotting, we studied dystrophin, spectrin and utrophin anomalies in the cardiac and skeletal muscles of 6-mo-old male DH. Age- and sex-matched CHF-148 strain albino normal hamsters (NH) served as controls. Sarcolemmal dystrophin staining was much weaker and interruptive in the DH. The densitometric analysis of the immunoblots revealed that dystrophin is reduced in DH by 83% in cardiac muscle (p < 0.0001), and by 50% in skeletal muscle (p < 0.0001). We conclude that sarcolemmal dystrophin distribution is markedly reduced and discontinuous in the cardiac and skeletal muscles of DH, with simultaneous upregulation of utrophin and a varied degree of spectrin labelling. This observation suggests that reduced sarcolemmal dystrophin is associated with membrane hyperpermeability, which leads to progressive muscle degeneration via EICA and segmental necrosis in DH. As in DMD, utrophin appears to play an important compensatory role in hamster dystrophinopathy.