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P B Simpson

Publications and source records attributed to P B Simpson.

18 recordsLinked to original sources
PubMed1998

Specialized distributions of mitochondria and endoplasmic reticulum proteins define Ca2+ wave amplification sites in cultured astrocytes.

This study was undertaken to examine the expression and role of the endoplasmic reticulum (ER) proteins calreticulin and ryanodine receptors, and mitochondria, in cultured astrocytes. Using several lines of investigation, we have identified a key role for mitochondria in astrocyte Ca2+ signalling: (1) a significant correlation was found between sites of regenerative Ca2+ wave amplification (possessing high amplitude ER Ca2+ release) and the location of mitochondria in the cell; (2) norepinephrine (2 microM) caused a rapid-onset increase in rhod 2 fluorescence in 34% of astrocyte mitochondria, indicating that cytosolic Ca2+ responses result in mitochondrial Ca2+ elevation; and (3) pretreatment with the protonophore carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone to inhibit mitochondrial activity markedly reduced the amplitude of subsequent norepinephrine-evoked cytosolic Ca2+ responses. We then investigated the roles of several ER proteins in Ca2+ signalling by immunocytochemistry. Ryanodine receptors and calreticulin were found to be expressed in heterogeneous patterns in astrocytes. The expression pattern of calreticulin corresponded closely with the distribution of mitochondria, whereas the expression of ryanodine receptors was not similar to that of either of these cellular factors. We measured Ca2+ wave kinetics in a single astrocyte, then assessed protein distribution by immunocytochemistry in the same cell. Cross-correlation between norepinephrine-evoked Ca2+ wave amplitude and calreticulin distribution indicated a close spatial relationship between this Ca2+-binding protein and sites of regenerative wave amplification. These results demonstrate that amplification sites for Ca2+ waves in astrocytes are identifiable by accumulations of calreticulin (and type 2 InsP3Rs), and by the presence of mitochondria, which may regulate the ER Ca2+ release process.

Animals↗
PubMed1998

Characterization of ryanodine receptors in oligodendrocytes, type 2 astrocytes, and O-2A progenitors.

In this study we have investigated the expression of ryanodine receptors (RyRs), and the ability of caffeine to evoke RyR-mediated elevation of intracellular Ca2+ levels ([Ca2+]i) in glial cells of the oligodendrocyte/type 2 astrocyte lineage. Immunocytochemistry with specific antibodies identified ryanodine receptors in cultured oligodendrocytes, type 2 astrocytes, and O-2A progenitor cells, at high levels in the perinuclear region and in a variegated pattern along processes. Glia acutely isolated from rat brain and in aldehydefixed sections of cortex were similarly found to express RyRs. Caffeine (5-50 mM) caused an increase in [Ca2+]i in most cultured type 2 astrocytes and in 50% of oligodendrocytes. Responses elicited by caffeine were inhibited by pretreatment with ryanodine (10 microM) or thapsigargin (1 microM), and the peak response was unaffected by removal of [Ca2+]o. O-2A progenitor cells, in contrast, were largely unresponsive to caffeine treatment. Pretreatment with kainate (200 microM) to activate Ca2+ entry increased the magnitude of caffeine-evoked [Ca2+]i elevations in type 2 astrocytes and oligodendrocytes, and caused caffeine to activate responses in a significant proportion of previously non-responding O-2A progenitors. In both type 2 astrocytes and oligodendrocytes, caffeine evoked Ca2+ changes which propagated as wavefronts from several initiation sites. These wave amplification sites were characterized by significantly higher local Ca2+ release kinetics. Our results indicate that several glial cell types express RyRs, and that their functionality differs within different cell types of the oligodendrocyte lineage. In addition, ionotropic glutamate receptor activation fills the caffeine-sensitive Ca2+ stores in these cells.

Animals↗
PubMed1998

Mitochondrial Ca2+ uptake and release influence metabotropic and ionotropic cytosolic Ca2+ responses in rat oligodendrocyte progenitors.

1. Many physiologically important activities of oligodendrocyte progenitor cells (O-2A cells), including proliferation, migration and differentiation, are regulated by cytosolic Ca2+ signals. However, little is known concerning the mechanisms of Ca2+ signalling in this cell type. We have studied the interactions between Ca2+ entry, Ca2+ release from endoplasmic reticulum and Ca2+ regulation by mitochondria in influencing cytosolic Ca2+ responses in O-2A cells. 2. Methacholine (MCh; 100 microM) activated Ca2+ waves that propagated from several initiation sites along O-2A processes. 3. During a Ca2+ wave evoked by MCh, mitochondrial membrane potential was often either depolarized (21 % of mitochondria) or hyperpolarized (20 % of mitochondria), as measured by changes in the fluorescence of 5,5',6,6'-tetrachloro-1,1',3, 3'-tetraethylbenzimidazole carbocyanine iodide (JC-1). 4. Stimulation with kainate (100 microM) evoked a slowly rising, sustained cytosolic Ca2+ elevation in O-2A cells. This also, in some cases, resulted in either a depolarization (15 % of mitochondria) or hyperpolarization (12 % of mitochondria) of mitochondrial membrane potential. 5. Simultaneous measurement of cytosolic (fluo-3 AM) and mitochondrial (rhod-2 AM) Ca2+ responses revealed that Ca2+ elevations in the cytosol evoked by either MCh or kainate were translated into long-lasting Ca2+ elevations in subpopulations of mitochondria. In some mitochondria, Ca2+ signals appeared to activate Ca2+ release into the cytosol. 6. Inhibition of the mitochondrial Na+-Ca2+ exchanger by CGP-37157 (25 microM) decreased kainate Ca2+ response amplitude and increased the rate of return of the response to basal Ca2+ levels. 7. Thus, both ionotropic and metabotropic stimulation evoke changes in mitochondrial membrane potential and Ca2+ levels in O-2A cells. Ca2+ uptake into some mitochondria is activated by Ca2+ entry into cells or release from stores. Mitochondrial Ca2+ release appears to play a key role in shaping kainate-evoked Ca2+ responses.

Animals↗
PubMed1998

Role of mitochondrial Ca2+ regulation in neuronal and glial cell signalling.

It is becoming increasingly clear that mitochondrial Ca2+ uptake from and release into the cytosol has important consequences for neuronal and glial activity. Ca2+ regulates mitochondrial metabolism, and mitochondrial Ca2+ uptake and release modulate physiological and pathophysiological cytosolic responses. In glial cells, inositol 1,4,5-trisphosphate-dependent Ca2+ responses are faithfully translated into elevations in mitochondrial Ca2+ levels, which modifies cytosolic Ca2+ wave propagation and may activate mitochondrial enzymes. The location of mitochondria within neurones may partially determine their role in Ca2+ signalling. Neuronal death due to NMDA-evoked Ca2+ entry can be delayed by an inhibitor of the mitochondrial permeability transition pore, and mitochondrial dysfunction is being increasingly implicated in a number of neurodegenerative conditions. These findings are illustrative of an emerging realization by neuroscientists of the importance of mitochondrial Ca2+ regulation as a modulator of cellular energetics, endoplasmic reticulum Ca2+ release and neurotoxicity.

Animals↗
PubMed1997

High density distribution of endoplasmic reticulum proteins and mitochondria at specialized Ca2+ release sites in oligodendrocyte processes.

In oligodendrocyte processes, methacholine-evoked Ca2+ waves propagate via regions of specialized Ca2+ release kinetics (wave amplification sites) at which the amplitude and rate of rise of local Ca2+ signals are markedly higher than in surrounding areas (Simpson, P. B., and Russell, J. T. (1996) J. Biol. Chem. 271, 33493-33501). In the present study we have examined the effects of other phosphoinositide-coupled agonists on Ca2+ in these cells, and the structural specializations underlying regenerative wave amplification sites. Both bradykinin and norepinephrine evoke Ca2+ waves, which initiate at the same loci and propagate through the cell body and multiple processes via identical wave amplification sites. Antibodies against type 2 inositol 1,4,5-trisphosphate receptors (InsP3R2) and calreticulin identify expression of these proteins in oligodendrocyte membranes in Western blots. Immunocytochemistry followed by high resolution fluorescence microscopy revealed that both InsP3R2 and calreticulin are expressed in high intensity patches along processes. Cross-correlation analysis of the profiles of local Ca2+ release kinetics during a Ca2+ wave and immunofluorescence for these proteins along cellular processes showed that the domains of high endoplasmic reticulum protein expression correspond closely to wave amplification sites. Staining cells with the mitochondrial dye, MitoTracker(R), showed that mitochondria are only found in intimate association with these sites possessing high density endoplasmic reticulum proteins, and they remain in the same locations over relatively long periods of time. It appears, therefore, that multiple specializations are found at domains of elevated Ca2+ release in oligodendrocyte processes, including high levels of calreticulin, InsP3R2 Ca2+ release channels, and mitochondria.

Amino Acid Sequence↗
PubMed1997

Role of sarcoplasmic/endoplasmic-reticulum Ca2+-ATPases in mediating Ca2+ waves and local Ca2+-release microdomains in cultured glia.

We have characterized the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA) pumps in cultured rat cortical type-1 astrocytes, type-2 astrocytes and oligodendrocytes. Perfusion with 10 microM cyclopiazonic acid (CPA) or 1 microM thapsigargin evoked a large and persistent elevation in cytosolic [Ca2+] in normal Ca2+-containing medium and a small and transient increase in nominally Ca2+-free medium. Subtraction of the response in Ca2+-free medium from that in the control revealed a slow-onset Ca2+-entry response to SERCA inhibition, which began after most of the store depletion had occurred. Thapsigargin- and CPA-induced responses propagated as Ca2+ waves, which began in several distinct cellular sites and travelled throughout the cell and through nearby cells, in confluent cultures. Propagation was supported by specialized Ca2+-release sites where the amplitude of the response was significantly higher and the rate of rise steeper. Such higher Ca2+-release kinetics were observed at these sites during Ins(1,4,5)P3-mediated Ca2+ waves in the same cells. Fluorescently tagged thapsigargin labelled SERCA pumps throughout glial cell bodies and processes. In oligodendrocyte processes, multiple domains with elevated SERCA staining were always associated with mitochondria. Our results are consistent with a model in which only a single Ca2+ store, expressing Ins(1,4,5)P3 receptors and SERCAs sensitive to both thapsigargin and CPA, is present in rat cortical glia, and indicate that inhibition of SERCA activates both Ca2+ release as a wavefront and Ca2+ entry via store-operated channels. The spatial relationship between SERCAs and mitochondria is likely to be important for regulating microdomains of elevated Ca2+-release kinetics.

Animals↗
PubMed1997

Neurotransmitter- and growth factor-induced cAMP response element binding protein phosphorylation in glial cell progenitors: role of calcium ions, protein kinase C, and mitogen-activated protein kinase/ribosomal S6 kinase pathway.

To understand how extracellular signals may produce long-term effects in neural cells, we have analyzed the mechanism by which neurotransmitters and growth factors induce phosphorylation of the transcription factor cAMP response element binding protein (CREB) in cortical oligodendrocyte progenitor (OP) cells. Activation of glutamate receptor channels by kainate, as well as stimulation of G-protein-coupled cholinergic receptors by carbachol and tyrosine kinase receptors by basic fibroblast growth factor (bFGF), rapidly leads to mitogen-activated protein kinase (MAPK) phosphorylation and ribosomal S6 kinase (RSK) activation. Kainate and carbachol activation of the MAPK pathway requires extracellular calcium influx and is accompanied by protein kinase C (PKC) induction, with no significant increase in GTP binding to Ras. Conversely, growth factor-stimulated MAPK phosphorylation is independent of extracellular calcium and is accompanied by Ras activation. Both basal and stimulated MAPK activity in OP cells are influenced by cytoplasmic calcium levels, as shown by their sensitivity to the calcium chelator bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid. The kinetics of CREB phosphorylation in response to the various agonists corresponds to that of MAPK activation. Moreover, CREB phosphorylation and MAPK activation are similarly affected by calcium ions. The MEK inhibitor PD 098059, which selectively prevents activation of the MAPK pathway, strongly reduces induction of CREB phosphorylation by kainate, carbachol, bFGF, and the phorbol ester TPA. We propose that in OPs the MAPK/RSK pathway mediates CREB phosphorylation in response to calcium influx, PKC activation, and growth factor stimulation.

Animals↗
PubMed1997

Comparison of type 2 inositol 1,4,5-trisphosphate receptor distribution and subcellular Ca2+ release sites that support Ca2+ waves in cultured astrocytes.

We have examined the mechanisms that underlie Ca2+ wave propagation in cultured cortical astrocytes. Norepinephrine evoked Ca2+ waves in astrocytes that began at discrete initiation loci and propagated throughout the cell by regenerative amplification at a number of cellular sites, as shown by very high Ca2+ release rates at these regions. We have hypothesized previously that domains displaying elevated Ca2+ release kinetics in astrocytes may correspond to sites of high inositol 1,4,5-trisphosphate receptor (InsP3R) density. To examine this possibility, we compared the distribution pattern of endoplasmic reticulum (ER) and InsP3Rs with Ca2+ release kinetics in subcellular regions during propagation of norepinephrine-evoked waves. 3,3'-Dihexyloxacarbocyanine iodide staining revealed that the ER in astrocytes exists as a meshwork of membranes extending throughout the cells, including fine processes. A specific antibody directed against type 2 InsP3Rs (InsP3R2) detected a 260-kDa band in western blotting of astrocyte membranes. Immunocytochemistry using this antibody stained the entire ER system in a punctate, variegated manner. When Ca2+ responses and InsP3R2 immunofluorescence were compared in the same cell, domains of elevated Ca2+ response kinetics (high amplitude and rapid rate of rise) showed significant positive correlation with high local intensity of InsP3R2 staining. It appears, therefore, that specializations in the ER responsible for discrete local Ca2+ release sites that support regenerative wave propagation include increased levels of InsP3R2 expression.

Animals↗
PubMed1996

Mitochondria support inositol 1,4,5-trisphosphate-mediated Ca2+ waves in cultured oligodendrocytes.

We have examined the spatial and temporal nature of Ca2+ signals activated via the phosphoinositide pathway in oligodendrocytes and the cellular specializations underlying oligodendrocyte Ca2+ response characteristics. Cultured cortical oligodendrocytes were incubated with fluo 3 or fura 2, and digital video fluorescence microscopy was used to study the effect of methacholine on [Ca2+]i. Single peaks, oscillations, and steady-state plateau [Ca2+]i elevations were evoked by increasing agonist concentration. The peaks and oscillations were found to be Ca2+ wave fronts, which propagate via distinct amplification regions in the cell where the kinetics of Ca2+ release (amplitude and rate of rise of response) are elevated. Staining with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolecarbocyanine++ + iodide (JC-1) and 3,3'-dihexyloxacarbocyanine iodide revealed that mitochondria are found in groups of three or more in oligodendrocyte processes and that the groups are distributed with considerable distance separating them. Cross-correlation analysis showed a high degree of correlation between sites where mitochondria are present and peaks in the amplitude and rate of rise of the Ca2+ response. Intramitochondrial Ca2+ concentration, measured using rhod 2, increased upon treatment with methacholine. Methacholine also evoked a rapid change in mitochondrial membrane potential as measured by the J-aggregate fluorescence of JC-1. Pretreatment with the mitochondrial inhibitors carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (1 microM, 2 min) or antimycin (2 microg/ml, 2 min) altered the methacholine-evoked Ca2+ response in most cells studied, responses being either markedly potentiated or inhibited. The results of this study demonstrate that stimulation of phosphoinositide-coupled muscarinic acetylcholinoceptors activates propagating Ca2+ wave fronts in oligodendrocytes and that the characteristics of these waves are dependent on mitochondrial location and function.

Animals↗
PubMed1996

Agonist-evoked Ca2+ mobilization from stores expressing inositol 1,4,5-trisphosphate receptors and ryanodine receptors in cerebellar granule neurones.

The mechanisms involved in Ca2+ mobilization evoked by the muscarinic cholinoceptor (mAChR) agonist carbachol (CCh) and N-methyl-D-aspartate (NMDA) in cerebellar granule cells have been investigated. An initial challenge with caffeine greatly reduced the subsequent intracellular Ca2+ concentration ([Ca2+]i) response to CCh (to 45 +/- 19% of the control), and, similarly, a much reduced caffeine response was detectable after prior stimulation with CCh (to 27 +/- 6% of the control). CCh-evoked [Ca2+]i responses were inhibited by preincubation with thapsigargin (10 microM), 2,5-di(tert-butyl)-1,4-benzohydroquinone (BHQ; 25 microM), ryanodine (10 microM), or dantrolene (25 microM). BHQ pretreatment was found to have no effect on the sustained phase of the NMDA-evoked [Ca2+]i response. Both CCh (1 mM) and 1-aminocyclopentane-1S,3R-dicarboxylic acid (ACPD; 200 microM) evoked a much diminished increase in [Ca2+]i in granule cells pretreated with CCh for 24 h compared with vehicle-treated control cells (CCh, 23 +/- 14%; ACPD, 27 +/- 1% of respective control values). In contrast, a 24-h CCh pretreatment decreased the subsequent inositol 1,4,5-trisphosphate (InsP3) response to CCh to a much greater extent compared with responses evoked by metabotropic glutamate receptor (mGluR) agonists; this suggests that the former effect on Ca2+ mobilization represents a heterologous desensitization of the mGluR-mediated response distal to the pathway second messenger. Furthermore, [Ca2+]i responses to caffeine and NMDA were unaffected by a 24-h pretreatment with CCh. This study indicates that ryanodine receptors, as well as InsP3 receptors, appear to be crucial to the mAChR-mediated [Ca2+]i response in granule cells. As BHQ apparently differentiates between the CCh- and NMDA-evoked responses, it is possible that the directly InsP3-sensitive pool is physically different from the ryanodine receptor pool. Also, activation of InsP3 receptors may not contribute significantly to NMDA-evoked elevation of [Ca2+]i in cerebellar granule cells. A model for the topographic organization of cerebellar granule cell Ca2+ stores is proposed.

Animals↗
PubMed1995

Divalent cation entry in cultured rat cerebellar granule cells measured using Mn2+ quench of fura 2 fluorescence.

In this study the rate of Mn2+ quench of fura-2 fluorescence evoked by glutamatergic and cholinergic agonists, depolarization and Ca2+ store modulators was measured in cultured cerebellar granule cells, in order to study their effects on Ca2+ entry in isolation from effects on Ca2+ store release. The rate of fluorescence quench by 0.1 mM Mn2+ was markedly increased by 25 mM K(+)-evoked depolarization or by 200 microM N-methyl-D-aspartate (NMDA), with a significantly greater increase occurring during the rapid-onset peak phase compared to the plateau phase of the K(+)- or NMDA-evoked [Ca2+]i response. The stimulatory effect of NMDA on Mn2+ quench was abolished by dizocilpine (10 microM), but nitrendipine (2 microM), while decreasing the rate of basal quench, did not affect NMDA-stimulated Mn2+ entry. This suggests that nitrendipine may not act on NMDA channels in granule cells, at least under these conditions, and that voltage-operated Ca2+ channels are involved in control quench whereas the NMDA-evoked quench is dependent on entry through the receptor channel. The t1/2 of quench was unaffected by alpha-amino-hydroxyisoxazole propionic acid (200 microM) and carbamyl choline (1 mM). Neither thapsigargin (10 microM) nor dantrolene (30 microM) significantly affected the rate of quench under control or NMDA- or K(+)-stimulated conditions, which confirms that the previously reported inhibitory effects on [Ca2+]i elevations evoked by these agents are due to actions on Ca2+ stores. However, thapsigargin elevated [Ca2+]i in the presence of normal [Ca2+]o but not in nominally Ca(2+)-free medium, indicating that it evokes Ca2+ entry in cerebellar granule cells, probably subsequent to store depletion, which appears to be either too small to be detected by Mn2+ quench or to occur via Mn(2+)-impermeant channels.

Animals↗
PubMed1995

Neuronal Ca2+ stores: activation and function.

The intracellular concentration of free Ca2+ ([Ca2+]i) displays complex fluctuations in response to a variety of stimuli, and acts as a pluripotent signal for many neuronal functions. It is well established that various 'metabotropic' neurotransmitter receptors can mediate the mobilization of Ca2+ stores via actions of inositol-polyphosphate second messengers, and more recent evidence suggests that 'ionotropic' receptor-mediated Ca2+ signals in neurones might also involve release of Ca2+ from intracellular stores. These two mechanisms of release of Ca2+ enable considerable temporal and spatial complexity of increases in the [Ca2+]i via multiple interactions at the level of intracellular-receptor activation. The complexity of Ca2+ signalling that is elicited via these interconnecting pathways might underlie mechanisms that are central to information transfer and integration within neuronal compartments.

Animals↗
PubMed1994

Potentiation of N-methyl-D-aspartate-evoked elevation of intracellular Ca2+ concentrations by exogenous glycine in cerebellar granule cells.

The effect of glycine on the intracellular free Ca2+ concentration ([Ca2+])i response to N-methyl-D-aspartate (NMDA) was examined in small groups of cerebellar granule cells loaded with fura 2. NMDA alone evoked a long-lasting monophasic [Ca2+]i plateau, which was abolished by removal of extracellular Ca2+, or addition of the NMDA channel antagonist dizocilpine or the glycine site antagonist 5,7-dichlorokynurenic acid, virtually unaffected by the L-type Ca2+ channel antagonist (-)-PN 202 791, and greatly, though variably, potentiated by addition of glycine. In the presence of glycine the response to NMDA was clearly biphasic. However, there was no consistent relationship between the magnitudes of the peak and plateau phases of the response, and their temporal relationship was also highly variable. The potentiation seen with exogenous glycine was highly dependent on plating density, which may be the result of higher levels of endogenous glycine in more dense cultures. Our results provide an explanation of the inconsistent findings previously reported by different groups on the potentiation of the [Ca2+]i response to NMDA by exogenous glycine.

Animals↗
PubMed1994

Chronic activation of muscarinic and metabotropic glutamate receptors down-regulates type I inositol 1,4,5-trisphosphate receptor expression in cerebellar granule cells.

The ability of receptors coupled to phosphoinositide turnover to evoke accumulation of inositol 1,4,5-trisphosphate (InsP3) over extended incubation periods, and consequently to affect the level of InsP3 receptor expression, was studied in cultured cerebellar granule cells. The cholinergic agonist carbachol (CCh; 1 mM) evoked a biphasic accumulation of InsP3, a rapid three- to fourfold peak increase over control levels at approximately 10 s, decreasing within 1 min to a long-lasting plateau elevation. Using an antibody against the type I InsP3 receptor, it was demonstrated that > 50% down-regulation of type I InsP3 receptor expression in cerebellar granule cells occurred within 1 h of incubation with 1 mM CCh. Over 24 h, 1 mM CCh caused an approximately 85% decrease in type I InsP3 receptor levels, and significant decreases in immunoreactivity were evident at much lower concentrations of CCh. Direct assessment of total InsP3 receptor expression using a radioligand binding method also detected down-regulation, but to an apparently lesser extent. 1-Aminocyclopentane-1S,3R-dicarboxylic acid (200 microM), an agonist of metabotropic glutamate receptors, evoked a marked decrease in type I InsP3 receptors after 24 h of incubation. These findings demonstrate that a functional consequence of maintained InsP3 production in cerebellar granule cells is the down-regulation of InsP3 receptor expression and that this down-regulation may be a common mechanism of action of phosphoinositide-linked receptors during prolonged stimulation.

Animals↗
PubMed1993

Involvement of intracellular stores in the Ca2+ responses to N-Methyl-D-aspartate and depolarization in cerebellar granule cells.

The [Ca2+]i of cerebellar granule cells can be increased in a biphasic manner by addition of NMDA or by depolarization (induced by elevating the extracellular K+ level), which both activate Ca2+ influx. The possibility that these stimuli activate Ca2(+)-induced Ca2+ release was investigated using granule cells loaded with fura 2-AM. Dantrolene, perfused onto groups of cells during the sustained plateau phase of the [Ca2+]i response to K+ or NMDA, was found to reduce the response to both agents in a concentration-dependent manner. Preincubation with thapsigargin (10 microM) substantially reduced the plateau phase of the [Ca2+]i response to K+ and both the peak and plateau phases of the NMDA response. Preincubation with ryanodine (10 microM) also reduced both the K(+)-evoked plateau response and both phases of the NMDA response. Neither had a consistent effect on the peak response to K+. The effects of thapsigargin and ryanodine on the NMDA response were partially additive. These results demonstrate that in cerebellar granule cells a major component of both K(+)- and NMDA-induced elevation of [Ca2+]i appears to be due to release from intracellular stores. The partial additivity of the effects of thapsigargin and ryanodine suggests that these agents affect two overlapping but nonidentical Ca2+ pools.

Animals↗
PubMed1977

Phospholipid monolayers and systemic lupus erythematosus.

A hypothesis is presented of the fundamental cause of the systemic lupus erythematosus. From a study of the molecular interaction of procainamide with phospholipid monolayers, it is proposed that the drug causes phospholipid loss from the cell membrane. Chronic phospholipid loss would lead to cell lysis and antinuclear antibody production.

Anesthetics, Local↗