Structural and biophysical determinants of single CaV3.1 and CaV3.2 T-type calcium channel inhibition by N2O

We investigated the biophysical mechanism of inhibition of recombinant T-type calcium channels Ca_V3.1 and Ca_V3.2 by nitrous oxide (N₂O). To identify functionally important channel structures, chimeras with reciprocal exchange of the N-terminal domains I and II and C-terminal domains III and IV were examined. In whole-cell recordings N₂O significantly inhibited Ca_V3.2, and – less pronounced – Ca_V3.1. A Ca_V3.2-prevalent inhibition of peak currents was also detected in cell-attached multi-channel patches. In cell-attached patches containing ≤3 channels N₂O reduced average peak current of Ca_V3.2 by decreasing open probability and open time duration. Effects on Ca_V3.1 were smaller and mediated by a reduced fraction of sweeps containing channel activity. Without drug, single Ca_V3.1 channels were significantly less active than Ca_V3.2. Chimeras revealed that domains III and IV control basal gating properties. Domains I and II, in particular a histidine residue within Ca_V3.2 (H191), are responsible for the subtype-prevalent N₂O inhibition. Our study demonstrates the biophysical (open times, open probability) and structural (domains I and II) basis of action of N₂O on Ca_V3.2. Such a fingerprint of single channels can help identifying the molecular nature of native channels. This is exemplified by a characterization of single channels expressed in human hMTC cells as functional homologues of recombinant Ca_V3.1.     

Fixed Dystonia in Complex Regional Pain Syndrome: a Descriptive and Computational Modeling Approach

Background  

Complex regional pain syndrome (CRPS) may occur after trauma, usually to one limb, and is characterized by pain and disturbed blood flow, temperature regulation and motor control. Approximately 25% of cases develop fixed dystonia. Involvement of dysfunctional GABAergic interneurons has been suggested, however the mechanisms that underpin fixed dystonia are still unknown. We hypothesized that dystonia could be the result of aberrant proprioceptive reflex strengths of position, velocity or force feedback.     

Mitochondrial 2,4-dienoyl-CoA Reductase Deficiency in Mice Results in Severe Hypoglycemia with Stress Intolerance and Unimpaired Ketogenesis

The mitochondrial β-oxidation system is one of the central metabolic pathways of energy metabolism in mammals. Enzyme defects in this pathway cause fatty acid oxidation disorders. To elucidate the role of 2,4-dienoyl-CoA reductase (DECR) as an auxiliary enzyme in the mitochondrial β-oxidation of unsaturated fatty acids, we created a DECR–deficient mouse line. In Decr^−/− mice, the mitochondrial β-oxidation of unsaturated fatty acids with double bonds is expected to halt at the level of trans-2, cis/trans-4-dienoyl-CoA intermediates. In line with this expectation, fasted Decr^−/− mice displayed increased serum acylcarnitines, especially decadienoylcarnitine, a product of the incomplete oxidation of linoleic acid (C_18:2), urinary excretion of unsaturated dicarboxylic acids, and hepatic steatosis, wherein unsaturated fatty acids accumulate in liver triacylglycerols. Metabolically challenged Decr^−/− mice turned on ketogenesis, but unexpectedly developed hypoglycemia. Induced expression of peroxisomal β-oxidation and microsomal ω-oxidation enzymes reflect the increased lipid load, whereas reduced mRNA levels of PGC-1α and CREB, as well as enzymes in the gluconeogenetic pathway, can contribute to stress-induced hypoglycemia. Furthermore, the thermogenic response was perturbed, as demonstrated by intolerance to acute cold exposure. This study highlights the necessity of DECR and the breakdown of unsaturated fatty acids in the transition of intermediary metabolism from the fed to the fasted state.     

A genetic system to assess in vivo the functions of histones and histone modifications in higher eukaryotes

Despite the fundamental role of canonical histones in nucleosome structure, there is no experimental system for higher eukaryotes in which basic questions about histone function can be directly addressed. We developed a new genetic tool for Drosophila melanogaster in which the canonical histone complement can be replaced with multiple copies of experimentally modified histone transgenes. This new histone‐replacement system provides a well‐defined and direct cellular assay system for histone function with which to critically test models in chromatin biology dealing with chromatin assembly, variant histone functions and the biological significance of distinct histone modifications in a multicellular organism.     

Single-channel activity and expression of atrial L-type Ca(2+) channels in patients with latent hyperthyroidism

Patients with "latent hyperthyroidism" (suppressed thyroid-stimulating hormone and normal circulating thyroid hormones) are at risk to develop atrial fibrillation. In animal models, hyperthyroidism is associated with increased cardiac L-type Ca(2+) current. Therefore, we assessed L-type channel function and expression in right atria from patients undergoing cardiac surgery. Single L-type channels were studied in the cell-attached condition. Voltage dependence of gating was similar in patients with and without latent hyperthyroidism. With use of a pulse protocol leading to maximum channel availability, single-channel activity was further analyzed. Average peak current was significantly enhanced in latent hyperthyroidism, mainly because of an increased channel availability (P < 0.05). Protein expression was analyzed by Western blot. In latent hyperthyroidism, expression of Ca(2+) channel alpha(1)-subunits was increased more than threefold (P < 0.01). In contrast, sarco(endo)plasmic reticulum Ca(2+)-ATPase and phospholamban levels were not significantly changed. We only observed a trend toward increased sarco(endo)plasmic reticulum Ca(2+)-ATPase expression (P = 0.085). Function and expression of human atrial L-type Ca(2+) channels are increased in latent hyperthyroidism. These endocrine effects on the heart may be clinically relevant.     

White and brown adipose stem cells: From signaling to clinical implications

Epidemiological studies estimate that by the year 2030, 2.16 billion people worldwide will be overweight and 1.12 billion will be obese [1]. Besides its now established function as an endocrine organ, adipose tissue plays a fundamental role as an energy storage compartment. As such, adipose tissue is capable of extensive expansion or retraction depending on the energy balance or disease state of the host, a plasticity that is unparalleled in other organs and – under conditions of excessive energy intake – significantly contributes to the afore mentioned obesity pandemic. Expansion of adipose tissue is driven by both hypertrophy and hyperplasia of adipocytes, which can renew frequently to compensate for cell death. This underlines the importance of adipocyte progenitor cells within the distinct adipose tissue depots to control both energy storage and endocrine functions of adipose tissue. Here we summarize recent findings on the identity and plasticity of adipose stem cells, the involved signaling cascades, and potential clinical implications of these cells for the treatment of metabolic dysfunction in obesity. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.