Regional heterogeneity in the ratio of α-MSH:β-endorphin in rat brain

The molar ratio of α-MSH:β-endorphin varies markedly among discrete microdissected regions of rat brain ranging from 0.57 in the median eminence to 2.74 in the lateral septum. This finding demonstrates that α-MSH and β-endorphin (β-END) are not uniformly distributed in a 1:1 molar ratio in rat brain as one might predict based on the consideration that the two peptides are synthesized in equimolar amounts as part of a common precursor molecule, pro-opiomelanocortin. The data indicate instead that the concentrations of α-MSH and β-END, the two predominant peptides expressed by opiomelantropinergic neurons, are independently regulated in rat brain. The heterogeneity of α-MSH:β-END ratios suggests that the regulation of α-MSH and β-END is regionally specific and may impart functional selectivity to the multisecretory opiomelanotropinergic neuronal system.     

L-type calcium channel β subunit modulates angiotensin II responses in cardiomyocytes

Angiotensin II regulation of L-type calcium currents in cardiac muscle is controversial and the underlying signaling events are not completely understood. Moreover, the possible role of auxiliary subunit composition of the channels in Angiotensin II modulation of L-type calcium channels has not yet been explored. In this work we study the role of Ca(v)β subunits and the intracellular signaling responsible for L-type calcium current modulation by Angiotensin II. In cardiomyocytes, Angiotensin II exposure induces rapid inhibition of L-type current with a magnitude that is correlated with the rate of current inactivation. Semi-quantitative PCR of cardiomyocytes at different days of culture reveals changes in the Ca(v)β subunits expression pattern that are correlated with the rate of current inactivation and with Angiotensin II effect. Over-expression of individual b subunits in heterologous systems reveals that the magnitude of Angiotensin II inhibition is dependent on the Ca(v)β subunit isoform, with Ca(v)β(1b) containing channels being more strongly regulated. Ca(v)β(2a) containing channels were insensitive to modulation and this effect was partially due to the N-terminal palmitoylation sites of this subunit. Moreover, PLC or diacylglycerol lipase inhibition prevents the Angiotensin II effect on L-type calcium channels, while PKC inhibition with chelerythrine does not, suggesting a role of arachidonic acid in this process. Finally, we show that in intact cardiomyocytes the magnitude of calcium transients on spontaneous beating cells is modulated by Angiotensin II in a Ca(v)β subunit-dependent manner. These data demonstrate that Ca(v)β subunits alter the magnitude of inhibition of L-type current by Angiotensin II.     

L-type calcium channel β subunit modulates angiotensin II responses in cardiomyocytes

Angiotensin II regulation of L-type calcium currents in cardiac muscle is controversial and the underlying signaling events are not completely understood. Moreover, the possible role of auxiliary subunit composition of the channels in Angiotensin II modulation of L-type calcium channels has not yet been explored. In this work we study the role of Ca_vβ subunits and the intracellular signaling responsible for L-type calcium current modulation by Angiotensin II. In cardiomyocytes, Angiotensin II exposure induces rapid inhibition of L-type current with a magnitude that is correlated with the rate of current inactivation. Semi-quantitative PCR of cardiomyocytes at different days of culture reveals changes in the Ca_vβ subunits expression pattern that are correlated with the rate of current inactivation and with Angiotensin II effect. Over-expression of individual b subunits in heterologous systems reveals that the magnitude of Angiotensin II inhibition is dependent on the Ca_vβ subunit isoform, with _Cavβ1bcontaining channels being more strongly regulated. _Cavβ2acontaining channels were insensitive to modulation and this effect was partially due to the N-terminal palmitoylation sites of this subunit. Moreover, PLC or diacylglycerol lipase inhibition prevents the Angiotensin II effect on L-type calcium channels, while PKC inhibition with chelerythrine does not, suggesting a role of arachidonic acid in this process. Finally, we show that in intact cardiomyocytes the magnitude of calcium transients on spontaneous beating cells is modulated by Angiotensin II in a Ca_vβ subunit-dependent manner. These data demonstrate that Ca_vβ subunits alter the magnitude of inhibition of L-type current by Angiotensin II.     

Immunolocalization of the acid-sensing ion channel 2a in the rat cerebellum

The acid-sensing ion channels (ASICs) are members of the DEG/ENaC superfamily of Na+ channels. Acid-gated cation currents have been detected in neurons from multiple regions of the brain including the cerebellum, but little is known about their molecular identity and function. Recently, one of ASICs (ASIC1a) was implicated in synaptic plasticity. In this study we examined the subcellular distribution of ASIC2a in rat cerebellum by immunostaining and confocal microscopy. Monoclonal antibodies for labeling of defined brain structures, for example, astroglia, Purkinje cell dendrites, nuclei, and presynaptic terminals were used for colocalization analyses. In the gray matter, the anti-ASIC2a antibody intensively stained dendrite branches of Purkinje cells evenly distributed throughout the entire molecular layer (ML). In the granule cell layer (GL), anti-ASIC2a antibody stained synaptic glomeruli. Neuronal localization of ASIC2a was confirmed by lack of co-staining with glial fibrillary acidic protein. Anti-ASIC2a staining in the ML colocalized with metabotropic glutamate receptor 1alpha (mGluR1alpha) in Purkinje cell dendrites and dendritic spines. Both proteins, mGluR1alpha and ASIC2a, were enriched in a crude synaptic membrane fraction prepared from cerebellum, suggesting synaptic expression of these proteins. Dual staining with anti-syntaxin 1A and anti-ASIC2a antibodies demonstrates characteristic complementary distribution of two proteins in both ML and GL. Because syntaxin 1A localized in presynaptic membranes and synaptic vesicles, complementary distribution with ASIC2a suggests postsynaptic localization of ASIC2a in these structures. This study shows specific localization of ASIC2a in both Purkinje and granule cell dendrites of the cerebellum and enrichment of ASIC2a in a crude cerebellar synaptic membrane fraction. The study is the first report of synaptic localization of ASIC2a in the CNS. The synaptic localization of ASIC2a in the cerebellum makes this channel a candidate for a role in motor coordination and learning.     

Dynamics of plasma−dust structures formed in a trap created in the narrowing of a current channel in a magnetic field

The geometry and dynamics of plasma?dust structures in a longitudinal magnetic field is studied experimentally. The structures are formed in a glow-discharge trap created in the double electric layer produced as a result of discharge narrowing by means of a dielectric insert introduced in the discharge tube. Studies of structures formed in the new type of glow-discharge trap are of interest from the standpoint of future experiments with complex plasmas in superstrong magnetic fields in which the dust component is magnetized. Different types of dielectric inserts were used: conical and plane ones with symmetric and asymmetric apertures. Conditions for the existence of stable dust structures are determined for dust grains of different density and different dispersity. According to the experimental results, the angular velocity of dust rotation is ≥10 s^–1, which is the fastest type of dust motion for all types of discharges in a magnetic field. The rotation is interpreted by analyzing the dynamics of individual dust grains.     

Dietary fat ingestion activates β-endorphin neurons in the hypothalamus

The opioid system regulates food choice, consumption, and reinforcement processes, especially for palatable meals such as fatty food. β-Endorphin is known as an endogenous opioid peptide produced in neurons of the hypothalamus. In this study, we found that Intralipid (fat emulsion) ingestion increased c-fos expression in β-endorphin neurons. However, intragastric infusion of Intralipid only slightly increased c-fos expression 2h after infusion. Further, dissection of glossopharyngeal nerve, innervating posterior tongue taste buds, partially but significantly decreased the Intralipid-induced c-fos expression. These results indicate that mainly the orosensory stimulation from fat may activate β-endorphin neurons, thereby promoting β-endorphin release.     

What does a common channel for electrolytes and non-electrolytes in the sperm mean?

Cell volume is central to osmoregulation in intact cells. Bovine spermatozoa, as also other mammalian spermatozoa, exhibit a very rapid regulatory volume decrease (RVD) when exposed to hypotonic saline media. This response, fastest known in animal cells, is mediated by a putative potassium channel which the pharmacological properties of a conventional channel and yet admits both electrolytes and non-electrolytes. The evolutionary basis and functional role of this conserved quinine-sensitive channel in mammalian sperm could offer hitherto unexplored facets of the link(s) between ecology and reproduction.     

The Gárdos channel: a review of the Ca2+-activated K+ channel in human erythrocytes

Ca²⁺-dependent K⁺ efflux from human erythrocytes was first described in the 1950s. Subsequent studies revealed that a K⁺-specific membrane protein (the Gárdos channel) was responsible for this phenomenon (the Gárdos effect). In recent years several types of Ca-activated K⁺ channel have been identified and studied in a wide range of cells, with the erythrocyte Gárdos channel serving as both a model for a broader physiological perspective, and an intriguing component of erythrocyte function.The existence of this channel has raised a number of questions. For example, what is its role in the establishment and maintenance of ionic distribution across the red cell membrane? What role might it play in erythrocyte development? To what extent is it active in circulating erythrocytes? What are the cell-physiological implications of its dysfunction?This review summarises current knowledge of this membrane protein with respect to its function and structure, its physiological roles (some putative) and its contribution to various disease states, and it provides an introduction to adaptable NMR methods, which is our own area of technical expertise, for such ion transport analysis.     

Acetyl-11-keto-β-boswellic acid modulates membrane dynamics in benzo(a)pyrene-induced lung carcinogenesis

Molecular and Cellular Biochemistry - Membrane fluidity is the most important physiochemical property of cell membranes and governs its functional attributes. The current investigations were...     

Segregation of a mutation in CNGB1 encoding the β-subunit of the rod cGMP-gated channel in a family with autosomal recessive retinitis pigmentosa

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of retinal diseases leading to blindness. By performing full genome linkage analysis in a consanguineous French family affected with severe autosomal recessive RP, we have excluded linkage to known loci involved in RP and mapped a novel locus to chromosome 16q13-q21 (Zmax=2.83 at theta=0 at the D16S3089 locus). Two candidate genes KIFC3 and CNGB1 mapping to this critical interval have been screened for mutations. The CNGB1 gene, which encodes the beta-subunit of the rod cGMP-gated channel, is mutated in the family presented in this study.     

β-endorphin: Effects on respiratory regulation

Intracisternal injection of 14.5 nmoles of human β-endorphin in lightly anesthetized dogs resulted in marked respiratory depression, manifested by diminished responses of ventilation and airway occlusion pressure to carbon dioxide rebreathing. These responses were temporarily reversed by intravenous injection of naloxone and attenuated following a second β-endorphin injection. Results in this study suggest a possible physiological role for endogenous opioid peptides in the regulation of respiration.     

Serotonergic mechanism in the control of β-endorphin and acth release in male rats

The role of the serotonergic mechanism in the regulation of β-endorphin (β-EP) and adrenocorticotropin (ACTH)-like immunoreactivity in plasma was investigated. Increases in β-EP and ACTH-LI produced by quipazine maleate (QPZ), a serotonergic agonist, 1 hr after injection could be completely prevented by the serotonin (5-HT) antagonist, cinanserin (CIN), which when injected alone, decreased basal plasma concentrations of both β-EP-LI and ACTH-LI. Concurrent injections of L-5-HTP with the 5-HT reuptake inhibitor, fluoxetine, produced an additive increase in plasma β-EP-LI 1 hr after injection. Injection of the 5-HT antagonist, cyproheptadine, significantly decreased plasma β-EP-LI. Stress by immobilization for 30 min or exposing the rats to 40° ± 1°C for 30 min produced an approximate 4-fold increase in plasma β-EP-LI and ACTH-LI, which was potentiated by I.P. injections of fluoxetine. Furthermore, the stress induced increases in plasma concentrations of β-EP-LI and ACTH-LI were significantly reduced by the serotonin antagonists metergoline and cinanserin. These results suggest that 5-HT is a potent stimulator of both β-EP and ACTH release and the increase in plasma concentrations of ACTH and β-EP induced by stress are probably mediated, at least in part, by central serotonergic mechanisms.     

β-endorphin release by angiotensin II: studies on the mechanism of action

Blood-borne angiotensin II induces release of β-endorphin-like immunoreactivity (β-EI) from rat anterior pituitary gland. To study the mechanism of action we investigated in rats the effect of transection of subfornical organ efferent projections on angiotensin-induced β-EI release in vivo and also the direct action of angiotensin II on β-EI release from isolated adenohypophyses in vitro. (i) No effect of transection of subfornical organ efferents on the increase in plasma β-EI following intravenous infusions of angiotensin II was found. (ii) When anterior pituitary quarters were continuously superfused in vitro, angiotensin II (1 – 10 nM) caused release of β-EI into the superfusion medium in a dose-dependent manner. The stimulatory effect of angiotensin II (3 nM) was blocked by the receptor antagonist saralasin (300 nM). We conclude that β-endorphin release by blood-borne angiotensin II, in contrast to other central effects of angiotensin, is not mediated by the subfornical organ; instead a direct action of angiotensin II on the adenohypophysis could be a mechanism of action responsible.     

Bursicon-α subunit modulates dLGR2 activity in the adult Drosophila melanogaster midgut independently to Bursicon-β

Bursicon is the main regulator of post molting and post eclosion processes during arthropod development. The active Bursicon hormone is a heterodimer of Burs-α and Burs-β. However, adult midguts express Burs-α to regulate the intestinal stem cell niche. Here, we examined the potential expression and function of its heterodimeric partner, Burs-β in the adult midgut. Unexpectedly, our evidence suggests that Burs-β is not significantly expressed in the adult midgut. burs-β mutants displayed the characteristic developmental defects but showed wild type-like adult midguts, thus uncoupling the developmental and adult phenotypes seen in burs-α mutants. Gain of function data and ex vivo experiments using a cAMP biosensor, demonstrated that Burs-α is sufficient to drive stem cell quiescence and to activate dLGR2 in the adult midgut.

Our evidence suggests that the post developmental transactivation of dLGR2 in the adult midgut is mediated by Burs-α and that the β subunit of Bursicon is dispensable for these activities.