Paxilline Prevents the Onset of Myotonic Stiffness in Pharmacologically Induced Myotonia: A Preclinical Investigation

Reduced Cl− conductance causes inhibited muscle relaxation after forceful voluntary contraction due to muscle membrane hyperexcitability. This represents the pathomechanism of myotonia congenita. Due to the prevailing data suggesting that an increased potassium level is a main contributor, we studied the effect of a modulator of a big conductance Ca2+- and voltage-activated K+ channels (BK) modulator on contraction and relaxation of slow- and high-twitch muscle specimen before and after the pharmacological induction of myotonia. Human and murine muscle specimens (wild-type and BK−/−) were exposed to anthracene-9-carboxylic acid (9-AC) to inhibit CLC-1 chloride channels and to induce myotonia in-vitro. Functional effects of BK-channel activation and blockade were investigated by exposing slow-twitch (soleus) and fast-twitch (extensor digitorum longus) murine muscle specimens or human musculus vastus lateralis to an activator (NS1608) and a blocker (Paxilline), respectively. Muscle-twitch force and relaxation times (T90/10) were monitored. Compared to wild type, fast-twitch muscle specimen of BK−/− mice resulted in a significantly decreased T90/10 in presence of 9-AC. Paxilline significantly shortened T90/10 of murine slow- and fast-twitch muscles as well as human vastus lateralis muscle. Moreover, twitch force was significantly reduced after application of Paxilline in myotonic muscle. NS1608 had opposite effects to Paxilline and aggravated the onset of myotonic activity by prolongation of T90/10. The currently used standard therapy for myotonia is, in some individuals, not very effective. This in vitro study demonstrated that a BK channel blocker lowers myotonic stiffness and thus highlights its potential therapeutic option in myotonia congenital (MC).</p

Isoform-specific regulation of mood behavior and pancreatic β cell and cardiovascular function by L-type Ca(2+) channels

Ca(v)1.2 and Ca(v)1.3 L-type Ca(2+) channels (LTCCs) are believed to underlie Ca(2+) currents in brain, pancreatic β cells, and the cardiovascular system. In the CNS, neuronal LTCCs control excitation-transcription coupling and neuronal plasticity. However, the pharmacotherapeutic implications of CNS LTCC modulation are difficult to study because LTCC modulators cause card iovascular (activators and blockers) and neurotoxic (activators) effects. We selectively eliminated high dihydropyridine (DHP) sensitivity from Ca(v)1.2 α1 subunits (Ca(v)1.2DHP–/–) without affecting function and expression. This allowed separation of the DHP effects of Ca(v)1.2 from those of Ca(v)1.3 and other LTCCs. DHP effects on pancreatic β cell LTCC currents, insulin secretion, cardiac inotropy, and arterial smooth muscle contractility were lost in Ca(v)1.2DHP–/– mice, which rules out a direct role of Ca(v)1.3 for these physiological processes. Using Ca(v)1.2DHP–/– mice, we established DHPs as mood-modifying agents: LTCC activator–induced neurotoxicity was abolished and disclosed a depression-like behavioral effect without affecting spontaneous locomotor activity. LTCC activator BayK 8644 (BayK) activated only a specific set of brain areas. In the ventral striatum, BayK-induced release of glutamate and 5-HT, but not dopamine and noradrenaline, was abolished. This animal model provides a useful tool to elucidate whether Ca(v)1.3-selective channel modulation represents a novel pharmacological approach to modify CNS function without major peripheral effects

Plasma concentrations of afamin are associated with the prevalence and development of metabolic syndrome

BACKGROUND: -Afamin is a human plasma vitamin E-binding glycoprotein primarily expressed in the liver and secreted into the bloodstream. Since little is known about (patho)-physiological functions of afamin, we decided to identify phenotypes associated with afamin by investigating transgenic mice overexpressing the human afamin gene and performing large-scale human epidemiological studies. METHODS AND RESULTS: -Transgenic mice overexpressing afamin revealed increased body weight and serum concentrations of lipids and glucose. We applied a random-effects meta-analysis using age- and sex-adjusted baseline and follow-up investigations in the population-based Bruneck (n=826), SAPHIR (n=1499), and KORA F4 studies (n=3060). Mean afamin concentrations were 62.5&plusmn;15.3, 66.2&plusmn;14.3, and 70.6&plusmn;17.2 mg/L in Bruneck, SAPHIR and KORA F4, respectively. Per 10 mg/L increment in afamin measured at baseline, the number of metabolic syndrome components increased by 19% (incidence rate ratio (IRR)=1.19 (95%CI 1.16-1.21), p=5.62&times;10(-64)). With the same afamin increment used at baseline we observed an 8% gain in metabolic syndrome components between baseline and follow-up (IRR=1.08 (95%CI 1.06-1.10), p=8.87&times;10(-16)). Afamin concentrations at baseline were highly significantly related to all individual metabolic syndrome components at baseline and follow-up. This observation was most pronounced for elevated waist circumference (OR=1.79 (95%CI 1.54-2.09), p=4.15&times;10(-14) at baseline and OR=1.46 (95%CI 1.31-1.63), p=2.84&times;10(-11) for change during follow-up) and for elevated fasting glucose concentrations (OR=1.46 (95%CI 1.40-1.52), p=1.87&times;10(-69), and OR=1.46 95%CI 1.24-1.71, p=5.13&times;10(-6), respectively). CONCLUSIONS: -This study in transgenic mice and more than 5,000 participants in epidemiological studies shows that afamin is strongly associated with the prevalence and development of metabolic syndrome and all its components