Acetazolamide prevents vacuolar myopathy in skeletal muscle of K(+) -depleted rats

The Community Pharmacy as a Study Center for the Epidemiological Analysis of the Population Vaccination against SARS-CoV-2: Evaluation of Vaccine Safety and Pharmaceutical Service

We conducted a monocentric observational study aimed at evaluating the vaccine safety and the pharmaceutical service provided at a community pharmacy (C.PHARM) in the Puglia Region in the period from 29 December 2021 to 12 March 2022 using data from 550 patients of various ages and sexes and with concomitant diseases. We collected anamnestic data, the number of hospitalizations, and any post-vaccination adverse reactions. Interviews using the integrated EQ5 method were also performed to evaluate the quality of the service offered and any therapy preference. As expected, the vaccines were reactogenic after the first dose in the patients with mild-moderate reactions, with younger age and female gender as risk factors. Immune-allergic reactions of a moderate-severe degree were observed in adult females. In the elderly, the vaccination was well tolerated. Comirnaty® showed a favorable O.R. < 1 vs. other vaccines. No cardiovascular events or hospitalizations were observed up to May 2023. Regional data indicate that all treatments during May 2023 were correlated with the viremia. PaxlovidTM was prescribed in 3% of the patients in our center and in 1.46% in the region, and distributed/dispensed on behalf of third parties in accordance with a novel distribution/dispensation protocol of the C.PHARM that resulted in a safe vaccination center providing appropriate patient inclusion during vaccination.

Hypokalemic periodic paralysis: a 3-year follow-up study

BACKGROUND AND OBJECTIVES

Primary hypokalemic periodic paralysis (HypoPP) is an inherited channelopathy most commonly caused by mutations in CACNA1S. HypoPP can present with different phenotypes: periodic paralysis (PP), permanent muscle weakness (PW), and mixed weakness (MW) with both periodic and permanent weakness. Little is known about the natural history of HypoPP.

METHODS

In this 3-year follow-up study, we used the MRC scale for manual muscle strength testing and whole-body muscle MRI (Mercuri score) to assess disease progression in individuals with HypoPP-causing mutations in CACNA1S.

RESULTS

We included 25 men (mean age 43 years, range 18-76 years) and 12 women (mean age 42 years, range 18-76 years). Two participants were asymptomatic, 21 had PP, 12 MW, and two PW. The median number of months between baseline and follow-up was 42 (range 26-52). Muscle strength declined in 11 patients during follow-up. Four of the patients with a decline in muscle strength had no attacks of paralysis during follow-up, and two of these patients had never had attacks of paralysis. Fat replacement of muscles increased in 27 patients during follow-up. Eight of the patients with increased fat replacement had no attacks of paralysis during follow-up, and two of these patients had never had attacks of paralysis.

DISCUSSION

The study demonstrates that HypoPP can be a progressive myopathy in both patients with and without attacks of paralysis.

Zoledronic Acid Blocks Overactive Kir6.1/SUR2-Dependent KATP Channels in Skeletal Muscle and Osteoblasts in a Murine Model of Cantú Syndrome

Cantú syndrome (CS) is caused by the gain of function mutations in the ABCC9 and KCNJ8 genes encoding, respectively, for the sulfonylureas receptor type 2 (SUR2) and the inwardly rectifier potassium channel 6.1 (Kir6.1) of the ATP-sensitive potassium (KATP) channels. CS is a multi-organ condition with a cardiovascular phenotype, neuromuscular symptoms, and skeletal malformations. Glibenclamide has been proposed for use in CS, but even in animals, the drug is incompletely effective against severe mutations, including the Kir6.1wt/V65M. Patch-clamp experiments showed that zoledronic acid (ZOL) fully reduced the whole-cell KATP currents in bone calvaria cells from wild type (WT/WT) and heterozygous Kir6.1wt/V65MCS mice, with IC50 for ZOL block < 1 nM in each case. ZOL fully reduced KATP current in excised patches in skeletal muscle fibers in WT/WT and CS mice, with IC50 of 100 nM in each case. Interestingly, KATP currents in the bone of heterozygous SUR2wt/A478V mice were less sensitive to ZOL inhibition, showing an IC50 of ~500 nM and a slope of ~0.3. In homozygous SUR2A478V/A478V cells, ZOL failed to fully inhibit the KATP currents, causing only ~35% inhibition at 100 μM, but was responsive to glibenclamide. ZOL reduced the KATP currents in Kir6.1wt/VMCS mice in both skeletal muscle and bone cells but was not effective in the SUR2[A478V] mice fibers. These data indicate a subunit specificity of ZOL action that is important for appropriate CS therapies.

Molecular Composition and Biological Activity of a Novel Acetonitrile-Water Extract of Lens Culinaris Medik in Murine Native Cells and Cell Lines Exposed to Different Chemotherapeutics Using Mass Spectrometry

We evaluated the effects of a new extract (70% acetonitrile, 2E0217022196DIPFARMTDA) of Lens culinaris Medik (Terre di Altamura SRL, Altamura BA) to prevent cytotoxic damage from cisplatin, staurosporine, irinotecan, doxorubicin, and the glucocorticoid dexamethasone. The acetonitrile-water extract (range 0.1-5 mg/mL) was obtained by extracting 10 g of lentil flour with 50 milliliters of the acetonitrile-water extraction mixture in a 70:30 ratio, first for 3 h and then overnight in a shaker at room temperature. The next day, the extract was filtered and passed through a Rotavapor to obtain only the aqueous component and eliminate that with acetonitrile, and then freeze-dried to finally have the powdered extract. In vitro experiments showed that the extract prevented the cytotoxic damage induced by cisplatin, irinotecan, and doxorubicin on HEK293 and SHSY5Y cell lines after 24-96 h. In murine osteoblasts after 24-72 h of incubation time, the extract was cytoprotective against all chemicals. The extract was effective against dexamethasone, leading to synergic cell proliferation in all cell types. In bone marrow cells, the extract is cytoprotective after 72 h against doxorubicin, staurosporine, and dexamethasone. Instead, on muscle fibers, the extract has a synergic effect with chemotherapeutics, increasing cytotoxicity induced by doxorubicin and staurosporine. LC-MS attested to the existence of several phenolic structures in the extract. The most abundant families of compounds were flavonoids (25.7%) and mellitic acid (18%). Thus, the development of this extract could be implemented in the area of research related to the chemoprevention of damage to renal, neuronal, bone marrow cells, and osteoblasts by chemotherapeutics; moreover, it could be used as a reinforcer of cytotoxic action of chemotherapeutics on muscle fibers.

Counteractions of a Novel Hydroalcoholic Extract from Lens Culinaria against the Dexamethasone-Induced Osteoblast Loss of Native Murine Cells

The cytoprotective effects of a novel hydroalcoholic extract (0.01–5 mg/mL) from Lens culinaria (Terre di Altamura Srl) were investigated within murine native skeletal muscle fibers, bone marrow cells, and osteoblasts, and in cell lines treated with the apoptotic agent staurosporine (2.14 × 10⁻⁶ M), the alkylating drug cisplatin (10⁻⁴ M), the topoisomerase I inhibitor irinotecan (10⁻⁴ M), the antimitotic pro-oxidant doxorubicin (10⁻⁶ M), and the immunosuppressant dexamethasone (2 × 10⁻⁶ M). An amount of 10g of plant material was used to obtain a 70% ethanol/water product, following two-step extraction, evaporation, lyophilization, and storage at −20 °C. For the murine osteoblasts, doxorubicin reduced survival by −65%, dexamethasone by −32% and −60% after 24 and 48 h of incubation time, respectively. The extract was effective in preventing the osteoblast count-reduction induced by dexamethasone; it was also effective at preventing the inhibition of mineralization induced by dexamethasone. Doxorubicin and cisplatin caused a significant reduction in cell growth by −77% for bone marrow cells, −43% for irinotecan, and −60% for dexamethasone, but there was no evidence for the cytoprotective effects of the extract in these cells. Staurosporine and doxorubicin caused a fiber death rate of >−40% after 18 and 24 h of incubation, yet the extract was not effective at preventing these effects. The extract was effective in preventing the staurosporine-induced reduction of HEK293 proliferation and colony formation in the crystal violet DNA staining and the clonogenic assays. It was also effective for the cisplatin-induced reduction in HEK293 cell proliferation. The extract, however, failed to protect the SHSY5Y neurons against cisplatin and irinotecan-induced cytotoxicity. A UV/VIS spectroscopy analysis showed three peaks at the wavelengths of 350, 260, and 190 nm, which correspond to flavonoids, proanthocyanins, salicylates, and AA, constituting the extract. These data suggest the possible development of this extract for use against dexamethasone-induced bone loss and renal chemotherapy-induced damage.

Targeted Therapies for Skeletal Muscle Ion Channelopathies: Systematic Review and Steps Towards Precision Medicine

BACKGROUND

Skeletal muscle ion channelopathies include non-dystrophic myotonias (NDM), periodic paralyses (PP), congenital myasthenic syndrome, and recently identified congenital myopathies. The treatment of these diseases is mainly symptomatic, aimed at reducing muscle excitability in NDM or modifying triggers of attacks in PP.

OBJECTIVE

This systematic review collected the evidences regarding effects of pharmacological treatment on muscle ion channelopathies, focusing on the possible link between treatments and genetic background.

METHODS

We searched databases for randomized clinical trials (RCT) and other human studies reporting pharmacological treatments. Preclinical studies were considered to gain further information regarding mutation-dependent drug effects. All steps were performed by two independent investigators, while two others critically reviewed the entire process.

RESULTS

For NMD, RCT showed therapeutic benefits of mexiletine and lamotrigine, while other human studies suggest some efficacy of various sodium channel blockers and of the carbonic anhydrase inhibitor (CAI) acetazolamide. Preclinical studies suggest that mutations may alter sensitivity of the channel to sodium channel blockers in vitro, which has been translated to humans in some cases. For hyperkalemic and hypokalemic PP, RCT showed efficacy of the CAI dichlorphenamide in preventing paralysis. However, hypokalemic PP patients carrying sodium channel mutations may have fewer benefits from CAI compared to those carrying calcium channel mutations. Few data are available for treatment of congenital myopathies.

CONCLUSIONS

These studies provided limited information about the response to treatments of individual mutations or groups of mutations. A major effort is needed to perform human studies for designing a mutation-driven precision medicine in muscle ion channelopathies.

Oxytocin/Osteocalcin/IL-6 and NGF/BDNF mRNA Levels in Response to Cold Stress Challenge in Mice: Possible Oxytonic Brain-Bone-Muscle-Interaction

Oxytocin (Oxt), osteocalcin (Ost), and NGF/BDNF have a role in bone homeostasis, reproduction, and cognition. Oxt/Ost is required for muscle repair. We investigated gene response of muscle and the inter-organ communication following cold stress (CS). The mRNA quantity of Ngf, Ost, Oxt, Bdnf, p75ntr, Ntrk1, Gprc6a, Oxtr, Ntrk2, UCP1, and Il-6 genes in bone, brain, soleus (SOL), and tibialis anterior (TA) muscles from adult mice following CS were investigated. The myosin heavy-chain Mhc2b, Mhc1, Mhc2x, and Mhc2a gene expression were investigated. Mice were maintained at T = 23°C or 4°C for 6 h and 5-days (5d). CS mice did not show signs of muscle degeneration. An upregulation of Ucp1 and Ngf genes by 2 and 1.5 folds, respectively, in TA after 6 h CS and Ntrk1 by 4 and 22 folds in SOL muscle after 6 h and 5d CS, respectively, was observed; while after 6 h CS p75Ntr was downregulated in either muscle. Bdnf was unaffected, while after 5d CS Ntrk2 was upregulated in TA. Ost was downregulated in SOL by 0.9-folds at 5d. Following 5d CS, Oxtr and Il-6 genes were upregulated, respectively, by 1 and 1.5 folds in SOL. A downregulation of Mhc2b, respectively, by 0.96 and 0.88-folds after 6 h and 5d CS in SOL and Mhc2a was also downregulated by 0.88-fold after 5d CS in TA. Mhc1 and Mhc2x were not affected. Changes in the expression levels of genes in TA and SOL muscles, bone, and brain following CS were regulated by IL6 and Oxt. CS potentiates the slow-twitch phenotype of SOL which is in line with the metabolic need of this muscle, and the potentiation of the slow-twitch phenotype in TA. Oxt and IL6 coordinate a phenotype-dependent tonic effect of slow-twitch muscle and Oxt regulates the inter-organ interaction between brain and SOL muscle. Muscle tropism is maintained by NGF signaling following CS.

Zoledronic Acid Modulation of TRPV1 Channel Currents in Osteoblast Cell Line and Native Rat and Mouse Bone Marrow-Derived Osteoblasts: Cell Proliferation and Mineralization Effect

Bisphosphonates (BPs) reduce bone pain and fractures by balancing the osteoblast/osteoclast ratio. The behavior of ion channels in the presence of BPs is not known. To investigate this, the effect of zoledronic acid BP (ZOL) (3 × 10⁻⁸ to 5 × 10⁻⁴ M) treatment, on ion channels, cell proliferation, and mineralization, has been investigated on preosteoclast-like cells, RAW264.7, preosteoblast-like cells MC3T3-E1, and rat/mouse native bone marrow-derived osteoblasts. In whole-cell patch clamp on cell line- and bone marrow-derived osteoblasts, ZOL potentiated outward currents. On RAW264.7, ZOL (10⁻⁴ M)-evoked current was reduced by the Kv channel blocker tetraethylammonium hydrochloride (TEA), but not by the selective TRPV1-channel antagonist capsazepine. On MC3T3-E1 cells and bone marrow-derived osteoblasts, ZOL-evoked current (5 × 10⁻⁸ to 10⁻⁴ M) was reduced by capsazepine, whereas the selective TRPV1-channel agonist capsaicin potentiated the control current. In the cell proliferation assay, 72 h incubation of RAW264.7 and MC3T3-E1 cells with ZOL reduced proliferation, with IC₅₀ values of 2.62 × 10⁻⁷ M and 2.02 × 10⁻⁵ M, respectively. Mineralization of MC3T3-E1 cells and bone marrow-derived osteoblasts was observed in the presence of capsaicin and ZOL (5 × 10⁻⁸–10⁻⁷ M); ZOL effects were antagonized by capsazepine. In summary, the ZOL-induced activation of TRPV1 channel mediates the mineralization of osteoblasts and counterbalances the antiproliferative effects, increasing the IC₅₀. This mechanism is not operative in osteoclasts lacking the TRPV1 channel.

Cell Cycle Regulation by Ca2+-Activated K⁺ (BK) Channels Modulators in SH-SY5Y Neuroblastoma Cells

The effects of Ca²⁺-activated K⁺ (BK) channel modulation by Paxilline (PAX) (10⁻⁷–10⁻⁴ M), Iberiotoxin (IbTX) (0.1–1 × 10⁻⁶ M) and Resveratrol (RESV) (1–2 × 10⁻⁴ M) on cell cycle and proliferation, AKT1p^Ser473 phosphorylation, cell diameter, and BK currents were investigated in SH-SY5Y cells using Operetta-high-content-Imaging-System, ELISA-assay, impedentiometric counting method and patch-clamp technique, respectively. IbTX (4 × 10⁻⁷ M), PAX (5 × 10⁻⁵ M) and RESV (10⁻⁴ M) caused a maximal decrease of the outward K⁺ current at +30 mV (Vm) of −38.3 ± 10%, −31.9 ± 9% and −43 ± 8%, respectively, which was not reversible following washout and cell depolarization. After 6h of incubation, the drugs concentration dependently reduced proliferation. A maximal reduction of cell proliferation, respectively of −60 ± 8% for RESV (2 × 10⁻⁴ M) (IC50 = 1.50 × 10⁻⁴ M), −65 ± 6% for IbTX (10⁻⁶ M) (IC50 = 5 × 10⁻⁷ M), −97 ± 6% for PAX (1 × 10⁻⁴ M) (IC50 = 1.06 × 10⁻⁵ M) and AKT1p^ser473 dephosphorylation was observed. PAX induced a G1/G2 accumulation and contraction of the S-phase, reducing the nuclear area and cell diameter. IbTX induced G1 contraction and G2 accumulation reducing diameter. RESV induced G2 accumulation and S contraction reducing diameter. These drugs share common actions leading to a block of the surface membrane BK channels with cell depolarization and calcium influx, AKT1p^ser473 dephosphorylation by calcium-dependent phosphatase, accumulation in the G2 phase, and a reduction of diameter and proliferation. In addition, the PAX action against nuclear membrane BK channels potentiates its antiproliferative effects with early apoptosis.

Gating Pore Currents in Sodium Channels

Voltage-gated sodium channels belong to the superfamily of voltage-gated cation channels. Their structure is based on domains comprising a voltage sensor domain (S1-S4 segments) and a pore domain (S5-S6 segments). Mutations in positively charged residues of the S4 segments may allow protons or cations to pass directly through the gating pore constriction of the voltage sensor domain; these anomalous currents are referred to as gating pore or omega (ω) currents. In the skeletal muscle disorder hypokalemic periodic paralysis, and in arrhythmic dilated cardiomyopathy, inherited mutations of S4 arginine residues promote omega currents that have been shown to be a contributing factor in the pathogenesis of these sodium channel disorders. Characterization of gating pore currents in these channelopathies and with artificial mutations has been possible by measuring the voltage-dependence and selectivity of these leak currents. The basis of gating pore currents and the structural basis of S4 movement through the gating pore has also been studied extensively with molecular dynamics. These simulations have provided valuable insight into the nature of S4 translocation and the physical basis for the effects of mutations that promote permeation of protons or cations through the gating pore.

Molecular structure and function of big calcium-activated potassium channels in skeletal muscle: pharmacological perspectives

The large-conductance Ca2+-activated K+ (BK) channel is broadly expressed in various mammalian cells and tissues such as neurons, skeletal muscles (sarco-BK), and smooth muscles. These channels are activated by changes in membrane electrical potential and by increases in the concentration of intracellular calcium ion (Ca2+). The BK channel is subjected to many mechanisms that add diversity to the BK channel α-subunit gene. These channels are indeed subject to alternative splicing, auxiliary subunits modulation, posttranslational modifications, and protein-protein interactions. BK channels can be modulated by diverse molecules that may induce either an increase or decrease in channel activity. The linkage of these channels to many intracellular metabolites and pathways, as well as their modulation by extracellular natural agents, have been found to be relevant in many physiological processes. BK channel diversity is obtained by means of alternative splicing and modulatory β- and γ-subunits. The association of the α-subunit with β- or with γ-subunits can change the BK channel phenotype, functional diversity, and pharmacological properties in different tissues. In the case of the skeletal muscle BK channel (sarco-BK channel), we established that the main mechanism regulating BK channel diversity is the alternative splicing of the KCNMA1/slo1 gene encoding for the α-subunit generating different splicing isoform in the muscle phenotypes. This finding helps to design molecules selectively targeting the skeletal muscle subtypes. The use of drugs selectively targeting the skeletal muscle BK channels is a promising strategy in the treatment of familial disorders affecting muscular skeletal apparatus including hyperkalemia and hypokalemia periodic paralysis.

Pharmacovigilance database search discloses ClC-K channels as a novel target of the AT1 receptor blockers valsartan and olmesartan

BACKGROUND AND PURPOSE

Human ClC-K chloride channels are highly attractive targets for drug discovery as they have a variety of important physiological functions and are associated with genetic disorders. These channels are crucial in the kidney as they control chloride reabsorption and water diuresis. In addition, loss-of-function mutations of CLCNKB and BSND genes cause Bartter's syndrome (BS), whereas CLCNKA and CLCNKB gain-of-function polymorphisms predispose to a rare form of salt sensitive hypertension. Both disorders lack a personalized therapy that is in most cases only symptomatic. The aim of this study was to identify novel ClC-K ligands from drugs already on the market, by exploiting the pharmacological side activity of drug molecules available from the FDA Adverse Effects Reporting System database.

EXPERIMENTAL APPROACH

We searched for drugs having a Bartter-like syndrome as a reported side effect, with the assumption that BS could be causatively related to the block of ClC-K channels. The ability of the selected BS-causing drugs to bind and block ClC-K channels was then validated through an integrated experimental and computational approach based on patch clamp electrophysiology in HEK293 cells and molecular docking simulations.

KEY RESULTS

Valsartan and olmesartan were able to block ClC-Ka channels and the molecular requirements for effective inhibition of these channels have been identified.

CONCLUSION AND IMPLICATIONS

These results suggest additional mechanisms of action for these sartans further to their primary AT₁ receptor antagonism and propose these compounds as leads for designing new potent ClC-K ligands.

A novel injectable formulation of 6-fluoro-l-DOPA imaging agent for diagnosis of neuroendocrine tumors and Parkinson's disease

Two [19F]F-l-DOPA (F-DOPA) new β-cyclodextrin (CD)-based dosage forms (FA and FB, respectively) have been studied and their physico-chemical and pharmacological features determined to overcome the administration site reactions showed by the currently used [18F]F-l-DOPA formulation (IASOdopa^®) to perform PET-CT diagnosis in oncology (neuroendocrine tumors) and neurological (Parkinson's disease) field. Chemical stability of FA and FB was found to be longer than IASOdopa^® by adding the thiol-antioxidant agent, L-Cysteine. ¹H and ¹⁹F NMR investigations suggest the formation of an inclusion complex of F-DOPA with β-CD. In vitro experiments on the effects of FA and FB on mouse skeletal muscle fibers and on the human neuroblastoma SH-SY5Y and embryonal kidney tsA201 cell lines viability showed that FA was the most performant formulation compared to F-DOPA solutions. In vivo tolerability tests of FA on adult male rat showed no significant effects on body weight and no change in their dried organs weight. In addition, their metabolic and physiological parameters were not affected. In conclusion, [18F]F-l-DOPA, formulated as FA, constitutes a promising dosage form for PET-CT diagnosis of both neuroendocrine tumors and Parkinson's disease.

Emerging role of calcium-activated potassium channel in the regulation of cell viability following potassium ions challenge in HEK293 cells and pharmacological modulation

Emerging evidences suggest that Ca²⁺activated-K⁺-(BK) channel is involved in the regulation of cell viability. The changes of the cell viability observed under hyperkalemia (15 mEq/L) or hypokalemia (0.55 mEq/L) conditions were investigated in HEK293 cells expressing the hslo subunit (hslo-HEK293) in the presence or absence of BK channel modulators. The BK channel openers(10^-11-10^-3M) were: acetazolamide(ACTZ), Dichlorphenamide(DCP), methazolamide(MTZ), bendroflumethiazide(BFT), ethoxzolamide(ETX), hydrochlorthiazide(HCT), quercetin(QUERC), resveratrol(RESV) and NS1619; and the BK channel blockers(2x10^-7M-5x10^-3M) were: tetraethylammonium(TEA), iberiotoxin(IbTx) and charybdotoxin(ChTX). Experiments on cell viability and channel currents were performed using cell counting kit-8 and patch-clamp techniques, respectively. Hslo whole-cell current was potentiated by BK channel openers with different potency and efficacy in hslo-HEK293. The efficacy ranking of the openers at -60 mV(Vm) was BFT> ACTZ >DCP ≥RESV≥ ETX> NS1619> MTZ≥ QUERC; HCT was not effective. Cell viability after 24 h of incubation under hyperkalemia was enhanced by 82+6% and 33+7% in hslo-HEK293 cells and HEK293 cells, respectively. IbTx, ChTX and TEA enhanced cell viability in hslo-HEK293. BK openers prevented the enhancement of the cell viability induced by hyperkalemia or IbTx in hslo-HEK293 showing an efficacy which was comparable with that observed as BK openers. BK channel modulators failed to affect cell currents and viability under hyperkalemia conditions in the absence of hslo subunit. In contrast, under hypokalemia cell viability was reduced by -22+4% and -23+6% in hslo-HEK293 and HEK293 cells, respectively; the BK channel modulators failed to affect this parameter in these cells. In conclusion, BK channel regulates cell viability under hyperkalemia but not hypokalemia conditions. BFT and ACTZ were the most potent drugs either in activating the BK current and in preventing the cell proliferation induced by hyperkalemia. These findings may have relevance in disorders associated with abnormal K⁺ ion homeostasis including periodic paralysis and myotonia.

Vacuolar myopathy in an adult Warmblood horse

Histopathological interpretation of semimembranosus muscle samples from an adult Warmblood mare with clinical signs suggestive of exertional rhabdomyolysis and intermittent mild elevations in muscle enzyme activities revealed abundant sarcoplasmic vacuoles in all fibre-types containing fine, apparently proteinaceous debris. Vacuolar contents stained lightly with PAS, but did not appear to contain amylopectate, lipid or acid phosphatase and their periphery was unstained with dystrophin immunohistochemistry. Electron microscopy revealed that vacuoles were not membrane bound. No vacuoles were detected in muscle samples evaluated at post mortem following 4 months of rest. To our knowledge, this is the first report of a presumed primary vacuolar myopathy in a horse.

Recent advances in the pathogenesis and drug action in periodic paralyses and related channelopathies

The periodic paralysis (PP) are rare autosomal-dominant disorders associated to mutations in the skeletal muscle sodium, calcium, and potassium channel genes characterized by muscle fiber depolarization with un-excitability, episodes of weakness with variations in serum potassium concentrations. Recent advances in thyrotoxic PP and hypokalemic PP (hypoPP) confirm the involvement of the muscle potassium channels in the pathogenesis of the diseases and their role as target of action for drugs of therapeutic interest. The novelty in the gating pore currents theory help to explain the disease symptoms, and open the possibility to more specifically target the disease. It is now known that the fiber depolarization in the hypoPP is due to an unbalance between the novel identified depolarizing gating pore currents (I_gp) carried by protons or Na⁺ ions flowing through aberrant alternative pathways of the mutant subunits and repolarizing inwardly rectifying potassium channel (Kir) currents which also includes the ATP-sensitive subtype. Abnormal activation of the I_gp or deficiency in the Kir channels predispose to fiber depolarization. One pharmacological strategy is based on blocking the I_gp without affecting normal channel gating. It remains safe and effective the proposal of targeting the K_ATP, Kir channels, or BK channels by drugs capable to specifically open at nanomolar concentrations the skeletal muscle subtypes with less side effects.

Effects of acetazolamide on transient K+ currents and action potentials in nodose ganglion neurons of adult rats

The aim of the present study was to determine whether acetazolamide (AZ) contributes to the inhibition of the fast inactivating transient K(+) current (I(A) ) in adult rat nodose ganglion (NG) neurons. We have previously shown that pretreatment with either AZ or 4-AP attenuated or blocked the CO(2) -induced inhibition of slowly adapting pulmonary stretch receptors in in vivo experiments. The patch-clamp experiments were performed by using the isolated NG neurons. In addition to this, the RT-PCR of mRNA and the expression of voltage-gated K(+) (Kv) 1.4, Kv 4.1, Kv 4.2, and Kv 4.3 channel proteins from nodose ganglia were examined. We used NG neurons sensitive to the 1 mM AZ application. The application of 1 mM AZ inhibited the I(A) by approximately 27% and the additional application of 4-AP (1 mM) further inhibited I(A) by 48%. The application of 0.1 μM α-dendrotoxin (α-DTX), a slow inactivating transient K(+) current (I(D) ) blocker, inhibited the baseline I(A) by approximately 27%, and the additional application of 1 mM AZ further decreased the I(A) by 51%. In current clamp experiments, AZ application (1 mM) increased the number of action potentials due to the decreased duration of the depolarizing phase of action potentials and/or due to a reduction in the resting membrane potential. Four voltage-gated K(+) channel proteins were present, and most (80-90%) of the four Kv channels immunoreactive neurons showed the co-expression of carbonic anhydrase-II (CA-II) immunoreactivity. These results indicate that the application of AZ causes the reduction in I(A) via the inhibition of four voltage-gated K(+) channel (Kv) proteins without affecting I(D).

Muscle channelopathies: does the predicted channel gating pore offer new treatment insights for hypokalaemic periodic paralysis?

Hypokalaemic periodic paralysis (hypoPP) is the archetypal skeletal muscle channelopathy caused by dysfunction of one of two sarcolemmal ion channels, either the sodium channel Nav1.4 or the calcium channel Cav1.1. Clinically, hypoPP is characterised by episodes of often severe flaccid muscle paralysis, in which the muscle fibre membrane becomes electrically inexcitable, and which may be precipitated by low serum potassium levels. Initial functional characterisation of hypoPP mutations failed to adequately explain the pathomechanism of the disease. Recently, as more pathogenic mutations involving loss of positive charge have been identified in the S4 segments of either channel, the hypothesis that an abnormal gating pore current may be important has emerged. Such an aberrant gating pore current has been identified in mutant Nav1.4 channels and has prompted potentially significant advances in this area. The carbonic anhydrase inhibitor acetazolamide has been used as a treatment for hypokalaemic periodic paralysis for over 40 years but its precise therapeutic mechanism of action is unclear. In this review we summarise the recent advances in the understanding of the molecular pathophysiology of hypoPP and consider how these may relate to the reported beneficial effects of acetazolamide. We also consider potential areas for future therapeutic development.

Skeletal muscle channelopathies: new insights into the periodic paralyses and nondystrophic myotonias

PURPOSE OF REVIEW

To summarize advances in our understanding of the clinical phenotypes, genetics, and molecular pathophysiology of the periodic paralyses, the nondystrophic myotonias, and other muscle channelopathies.

RECENT FINDINGS

The number of pathogenic mutations causing periodic paralysis, nondystrophic myotonias, and ryanodinopathies continues to grow with the advent of exon hierarchy analysis strategies for genetic screening and better understanding and recognition of disease phenotypes. Recent studies have expanded and clarified the role of gating pore current in channelopathy pathogenesis. It has been shown that the gating pore current can account for the molecular and phenotypic diseases observed in the muscle sodium channelopathies, and, given that homologous residues are affected in mutations of calcium channels, it is possible that pore leak represents a pathomechanism applicable to many channel diseases. Improvements in treatment of the muscle channelopathies are on the horizon. A randomized controlled trial has been initiated for the study of mexiletine in nondystrophic myotonias. The class IC antiarrhythmia drug flecainide has been shown to depress ventricular ectopy and improve exercise capacity in patients with Andersen-Tawil syndrome.

SUMMARY

Recent studies have expanded our understanding of gating pore current as a disease-causing mechanism in the muscle channelopathies and have allowed new correlations to be drawn between disease genotype and phenotype.

Methazolamide does not impair respiratory work performance in anesthetized rabbits

In human medicine, the carbonic anhydrase (CA) inhibitor acetazolamide is used to treat irregular breathing disorders. Previously, we demonstrated in the rabbit that this substance stabilized closed-loop gain properties of the respiratory control system, but concomitantly weakened respiratory muscles. Among others, the highly diffusible CA-inhibitor methazolamide differs from acetazolamide in that it fails to activate Ca2+-dependent potassium channels in skeletal muscles. Therefore, we aimed to find out, whether or not methazolamide may exert attenuating adverse effects on respiratory muscle performance as acetazolamide. In anesthetized spontaneously breathing rabbits ( n = 7), we measured simultaneously the CO2 responses of tidal phrenic nerve activity, tidal transpulmonary pressure changes, and tidal volume before and after intravenous application of methazolamide at two mean (± SE) cumulative doses of 3.5 ± 0.1 and 20.8 ± 0.4 mg/kg. Similar to acetazolamide, low- and high-dose methazolamide enhanced baseline ventilation by 52 ± 10% and 166 ± 30%, respectively ( P < 0.01) and lowered the base excess in a dose-dependent manner by up to 8.3 ± 0.9 mmol/l ( P < 0.001). The transmission of a CO2-induced rise in phrenic nerve activity into volume and/or pressure and, hence, respiratory work performance was 0.27 ± 0.05 ml·kg−1·kPa·unit−1 under control conditions, but remained unchanged upon low- or high-dose methazolamide, at 0.30 ± 0.06 and 0.28 ± 0.07 ml·kg−1·kPa·unit−1, respectively. We conclude that methazolamide does not cause respiratory muscle weakening at elevated levels of ventilatory drive. This substance (so far not used for medication of respiratory diseases) may thus exert stabilizing influences on breathing control without adverse effects on respiratory muscle function.

K+-dependent paradoxical membrane depolarization and Na+ overload, major and reversible contributors to weakness by ion channel leaks

Normal resting potential (P1) of myofibers follows the Nernst equation, exhibiting about -85 mV at a normal extracellular K(+) concentration ([K(+)](o)) of 4 mM. Hyperpolarization occurs with decreased [K(+)](o), although at [K(+)](o) < 1.0 mM, myofibers paradoxically depolarize to a second stable potential of -60 mV (P2). In rat myofiber bundles, P2 also was found at more physiological [K(+)](o) and was associated with inexcitability. To increase the relative frequency of P2 to 50%, [K(+)](o) needed to be lowered to 1.5 mM. In the presence of the ionophore gramicidin, [K(+)](o) reduction to only 2.5 mM yielded the same effect. Acetazolamide normalized this increased frequency of P2 fibers. The findings mimic hypokalemic periodic paralysis (HypoPP), a channelopathy characterized by hypokalemia-induced weakness. Of myofibers from 7 HypoPP patients, up to 25% were in P2 at a [K(+)](o) of 4 mM, in accordance with their permanent weakness, and up to 99% were in P2 at a [K(+)](o) of 1.5 mM, in accordance with their paralytic attacks. Of 36 HypoPP patients, 25 had permanent weakness and myoplasmic intracellular Na(+) ([Na(+)](i)) overload (up to 24 mM) as shown by in vivo (23)Na-MRI. Acetazolamide normalized [Na(+)](i) and increased muscle strength. HypoPP myofibers showed a nonselective cation leak of 12-19.5 microS/cm(2), which may explain the Na(+) overload. The leak sensitizes myofibers to reduced serum K(+), and the resulting membrane depolarization causes the weakness. We postulate that the principle of paradoxical depolarization and loss of function upon [K(+)](o) reduction may apply to other tissues, such as heart or brain, when they become leaky (e.g., because of ischemia).