Influence of ethanol on calcium,inositol phospholipids and intracellular signalling mechanisms

Summary Studies have implicated Ca⁺⁺ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca⁺⁺ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca⁺⁺/Mg⁺⁺-ATPase, the high affinity membrane Ca⁺⁺ pump.Current research suggests that a subtype of the voltage-dependent Ca⁺⁺ channel, the dihydropyridine-sensitive Ca⁺⁺ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases⁴⁵Ca⁺⁺-influx and [³H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca⁺⁺/Mg⁺⁺-ATPase activity in neuronal membranes. Changes in Ca⁺⁺ channel and Ca⁺⁺/Mg⁺⁺-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca⁺⁺ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca⁺⁺/Mg⁺⁺-ATPase activity.The increased sensitivity of three Ca⁺⁺-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.     

Molecular mechanisms of lipoprotein receptor signalling

The low-density lipoprotein (LDL) receptor is the prototype of a classical endocytosis receptor that mediates the uptake of extracellular ligands. Other members of the LDL receptor gene family, on the other hand, have been shown to regulate intracellular signalling cascades. Among these are the LDL receptor-related protein 1, LRP1, a promiscuous and ubiquitously expressed receptor which is critically involved in a multitude of diverse physiological processes; the Reelin receptors ApoER2 and VLDL receptor, which participate in neuronal development; and megalin, a multifunctional receptor expressed in various epithelia. In this review, we focus on recent developments that highlight similarities and differences between these related receptors and their biological function, and discuss open questions as to the underlying molecular mechanisms.     

Pharmacological inhibition of store-operated calcium entry in MDA-MB-468 basal A breast cancer cells: consequences on calcium signalling,cell migration and proliferation

Store-operated Ca²⁺ entry is a pathway that is remodelled in a variety of cancers, and altered expression of the components of store-operated Ca²⁺ entry is a feature of breast cancer cells of the basal molecular subtype. Studies of store-operated Ca²⁺ entry in breast cancer cells have used non-specific pharmacological inhibitors, complete depletion of intracellular Ca²⁺ stores and have mostly focused on MDA-MB-231 cells (a basal B breast cancer cell line). These studies compared the effects of the selective store-operated Ca²⁺ entry inhibitors Synta66 and YM58483 (also known as BTP2) on global cytosolic free Ca²⁺ ([Ca²⁺]_CYT) changes induced by physiological stimuli in a different breast cancer basal cell line model, MDA-MB-468. The effects of these agents on proliferation as well as serum and epidermal growth factor (EGF) induced migration were also assessed. Activation with the purinergic receptor activator adenosine triphosphate, produced a sustained increase in [Ca²⁺]_CYT that was entirely dependent on store-operated Ca²⁺ entry. The protease activated receptor 2 activator, trypsin, and EGF also produced Ca²⁺ influx that was sensitive to both Synta66 and YM58483. Serum-activated migration of MDA-MB-468 breast cancer cells was sensitive to both store-operated Ca²⁺ inhibitors. However, proliferation and EGF-activated migration was differentially affected by Synta66 and YM58483. These studies highlight the need to define the exact mechanisms of action of different store-operated calcium entry inhibitors and the impact of such differences in the control of tumour progression pathways.     

Influence of diuretics on renal calcium excretion

Zusammenfassung Die renale Kalziumausscheidung wird bei einmaliger i.v. Zufuhr von Aminophyllin, Furosemid, Etacrynsäure, Azetazolamid und Chlorothiazid erhöht. Dies kann nicht nur durch die erhöhte Natriumausscheidung erklärt werden, sondern muss mit dem direkten tubulären Kalziumtransport im Zusammenhang stehen.     

The action of the peptidoleukotriene LTD4 on intracellular calcium in rat mesangial cells

The dose-dependent effect of CGP 45715A on the LTD₄-induced Ca²⁺ response of glomerular mesangial cells has been studied. Our results demonstrate that the LTD₄-dependent increase in the cytosolic Ca²⁺ concentration primarily involves an InsP₃-mediated release of Ca²⁺ from intracellular storage sites and to a minor extent an enhanced influx of Ca²⁺ through receptor-operated Ca²⁺ channels located in the plasma membrane. The action of CGP 45715A on the Ca²⁺ response is an inhibitory one and is convincingly explained by a displacement of LTD₄ from its receptor site(s). The contractile effect of LTD₄ on pulmonary smooth muscle is proposed to be mainly caused by a receptor-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate.     

Influence of hypoxia on contractility and calcium uptake in rabbit aorta

Summary The influence of hypoxia on noradrenaline (NA)-induced contractions and⁴⁵Ca uptake has been studied on isolated rabbit aortae. Hypoxia significantly decreased the contractility of aortic strips. NA stimulation resulted in increased or decreased⁴⁵Ca uptake by normoxic or hypoxic specimens, respectively. Relating⁴⁵Ca movement with mechanical activity, the results suggest that decrease in Ca⁺⁺ uptake may be mechanism for hypoxic relaxation of aortic smooth muscle.The author acknowledges facilities at the Wellcome Surgical Research Institute, University of Glasgow, U.K. Much of this work was in collaboration with Drs Sheila Jennett and J.D. Pickard.     

Inhibition of calcium transport in mitochondria byβ-receptor blocking substances and its reactivation by phospholipids

Zusammenfassung -Rezeptorenblocker hemmen den aktiven Kalziumtransport an isolierten Herzmitochondrien und den phospholipidvermittelten Kalziumtransport in Ausschüttelungsversuchen. Die Hemmung des mitochondrialen Kalziumtransportes lässt sich durch Phosphatidylserin und weniger stark durch Lecithin (10^–4 g/ml) aufheben, während andere Phospholipide und deren Bausteine wirkungslos sind.

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Parts of this study were presented at the Symposium on Calcium and the Heart of the International Study Group for Research in Cardiac Metabolism held at London on the 6th September 1970.     

Influence of ethanol on thyroxine accumulation in the hypothalamus,pituitary gland and cerebrospinal fluid in the newborn rabbit

Summary The effect of ethanol on thyroxine (T₄) accumulation in the hypothalamus (H), pituitary gland (P) and cerebrospinal fluid (CSF) has been investigated in 1–15-day-old rabbits. It has been found that H or CSF serum ratios decreased with age by about 2 in the course of 13 postnatal days. Stable T₄ resulted in an increase of¹²⁵I-T₄ in H, P and CSF. Ethanol per se caused an increase in transfer and accumulation of radiothyroxine or made the changes after loading animals with carrier T₄ more pronounced.     

Features on intracellular calcium distribution in the adipose tissue of spontaneously hypertensive rats (SHR)

Summar The in vitro study of the kinetics of⁴⁵Ca effux from adipose tissue of rats reveale 3 pools of exchangeable calcium. Calcium content in the intracellular pools of adipose tissue of spontaneously hypertensive rats is increased as compared to that in normotensive controls.     

Studies on the mechanisms of neurulation in the chick: The intracellular distribution of Ca++1

Summary Coated vesicles were found to accumulate Ca⁺⁺ in neuroepithelial cells and may play a role in regulating the contractile activities of apical microfilament bundles during uplifting of neural folds in the chick.This study was supported in part by grants from the Research Council and the Charles and Johanna Busch Memorial Fund of Rutgers University.     

Effect of phospholipids on purified lipoamidase

Summary Phospholipids were added to purified lipoamidase from porcine brain microsomal membranes, and changes in lipoamidase activity were examined. Approximately twofold activation of lipoamidase activity occurred upon the addition of phosphatidylethanolamine. On the other hand, phosphosphatidylserine, cardiolipin, and phosphatidic acid reduced the enzyme activity by approximately 80%. This pattern of the activation of lipoamidase by phosphatidylethanolamine and its inhibition by phosphatidylserine is similar to the pattern for adenylate cyclase, and contrasts with the pattern for ATPase.     

Effect of phospholipids on purified lipoamidase

Phospholipids were added to purified lipoamidase from porcine brain microsomal membranes, and changes in lipoamidase activity were examined. Approximately twofold activation of lipoamidase activity occurred upon the addition of phosphatidylethanolamine. On the other hand, phosphatidylserine, cardiolipin, and phosphatidic acid reduced the enzyme activity by approximately 80%. This pattern of the activation of lipoamidase by phosphatidylethanolamine and its inhibition by phosphatidylserine is similar to the pattern for adenylate cyclase, and contrasts with the pattern for ATPase.     

Role of intracellular symbionts in the fatbody of cockroaches: Influence on hemolymph proteins

Zusammenfassung Zur Herabsetzung der Anzahl von Symbionten in einem Fettkörper der KüchnschabeBlaberus craniifer wurde eine Penicillin-G-Behandlung durchgeführt, was eine Reduktion bei 2 Hämolymphe-Proteinen verursachte. Diese mit der Symbionten-Aktivität und Fortpflanzung verknüpften Proteine treten am Ende der Behandlung wieder in Erscheinung.     

Emerging mechanisms and consequences of calcium regulation of alternative splicing in neurons and endocrine cells

Alternative splicing contributes greatly to proteomic complexity. How it is regulated by external stimuli to sculpt cellular properties, particularly the highly diverse and malleable neuronal properties, is an underdeveloped area of emerging interest. A number of recent studies in neurons and endocrine cells have begun to shed light on its regulation by calcium signals. Some mechanisms include changes in the trans-acting splicing factors by phosphorylation, protein level, alternative pre-mRNA splicing, and nucleocytoplasmic redistribution of proteins to alter protein–RNA or protein–protein interactions, as well as modulation of chromatin states. Importantly, functional analyses of the control of specific exons/splicing factors in the brain point to a crucial role of this regulation in synaptic maturation, maintenance, and transmission. Furthermore, its deregulation has been implicated in the pathogenesis of neurological disorders, particularly epilepsy/seizure. Together, these studies have not only provided mechanistic insights into the regulation of alternative splicing by calcium signaling but also demonstrated its impact on neuron differentiation, function, and disease. This may also help our understanding of similar regulations in other types of cells.