Functional recovery of consumers discharged from mental hospital and participating in a community-based psychosocial programme provided by a non-governmental organisation

OBJECTIVE

To explore the 1-year functional recovery rate and identify factors predicting functional recovery of consumers in the Hong Kong context.

METHODS

By adopting a prospective longitudinal follow-up research design, a cohort of Chinese people discharged from the mental hospital and participating in a community-based psychosocial programme provided by a non-governmental organisation were followed up for 1 year. These individuals were assessed on their social functioning, psychiatric symptoms, self-efficacy, and quality of life using standardised assessment scales at baseline, 6 months, and 12 months of follow-up.

RESULTS

Of 87 participants, about one quarter (23.0%, n = 20) achieved functional recovery and about three quarters (79.3%, n = 69) achieved symptom remission at 12 months of follow-up. Also, the group showing functional recovery achieved better quality of life than those not showing recovery. Logistic regression analysis indicated that current functioning, current psychiatric symptoms, and achieving open employment at 12 months were significant predictors of functional recovery. These 3 predicting factors altogether accounted for half (54.4%) of the variance of functional recovery.

CONCLUSIONS

It is more difficult to achieve functional recovery than symptom remission for consumers. Helping consumers to improve social skills, achieve open employment, and reduce psychiatric symptoms is recommended as important elements in facilitating functional recovery in the local context.

The plasma membrane Na+/Ca2+ exchanger is cleaved by distinct protease families in neuronal cell death

Neurodegenerative conditions commonly involve loss of neuronal connectivity, synaptic dysfunction with excessive pruning, and ionic imbalances. These often serve as a prelude to cell death either through the activation of apoptotic or necrotic death routines or excess autophagy. In many instances, a local or generalized Ca2+ deregulation is involved in signaling or executing cell death. We have recently shown that in brain ischemia, and during excitotoxicity triggered by excess glutamate, the irreversible Ca2+ deregulation leading to necrosis is due to calpain-mediated modulation of the plasma membrane Na+/Ca2+ exchanger (NCX). Here we show that the NCX can also be cleaved by caspases in neurons undergoing apoptosis, which suggests that cleavage of the main Ca2+ extrusion pathway is a lethal event in multiple forms of cell death.

Sphingosine 1-phosphate: a Ca2+ release mediator in the balance

Sphingosine 1-phosphate (S1P) is a lipid signalling molecule with Ca(2+) mobilising properties. Importantly for a role as a Ca(2+) release messenger, intracellular levels of S1P can be regulated by a variety of extracellular stimuli, via the enzyme sphingosine kinase. However, neither the mechanism underlying S1P generation, nor its actions at the endoplasmic reticulum are clear. Thus, the role of S1P as an intracellular mediator of Ca(2+) release remains in the balance.

Calcium puffs are generic InsP3-activated elementary calcium signals and are downregulated by prolonged hormonal stimulation to inhibit cellular calcium responses

Elementary Ca2+ signals, such as ‘Ca2+ puffs’, which arise from the activation of inositol 1,4,5-trisphosphate receptors, are building blocks for local and global Ca2+ signalling. We characterized Ca2+ puffs in six cell types that expressed differing ratios of the three inositol 1,4,5-trisphosphate receptor isoforms. The amplitudes, spatial spreads and kinetics of the events were similar in each of the cell types. The resemblance of Ca2+ puffs in these cell types suggests that they are a generic elementary Ca2+ signal and, furthermore, that the different inositol 1,4,5-trisphosphate isoforms are functionally redundant at the level of subcellular Ca2+ signalling. Hormonal stimulation of SH-SY5Y neuroblastoma cells and HeLa cells for several hours downregulated inositol 1,4,5-trisphosphate expression and concomitantly altered the properties of the Ca2+ puffs. The amplitude and duration of Ca2+ puffs were substantially reduced. In addition, the number of Ca2+ puff sites active during the onset of a Ca2+ wave declined. The consequence of the changes in Ca2+ puff properties was that cells displayed a lower propensity to trigger regenerative Ca2+ waves. Therefore, Ca2+ puffs underlie inositol 1,4,5-trisphosphate signalling in diverse cell types and are focal points for regulation of cellular responses.

Shift in diurnal feeding patterns in nursing home residents with Alzheimer's disease

BACKGROUND

Individuals with Alzheimer's disease (AD) are highly susceptible to weight loss and malnutrition, which, to date, have not been associated with decreased food consumption. The current study examined food intake patterns and how they change in relation to body mass index (BMI), behavioral function, and cognitive status in institutionalized seniors with AD.

METHODS

Twenty-one consecutive days of investigator-weighed food intake collections were conducted on 25 subjects with likely AD residing at a home for the aged. All subjects maintained the ability to self-feed.

RESULTS

Eighty-eight percent of participants did not meet targeted energy needs, including an estimated 37% prevalence of protein inadequacy. Subjects with increased behavioral difficulties, based on the London Psychogeriatric Rating Scale, had reduced meal-related intakes that were highly associated with decreased energy consumption at dinner. With behavioral changes, particularly increased mental disorganization and confusion, there was a shift in circadian eating patterns such that the greatest proportion of daily energy was consumed at breakfast. Individuals with low BMIs tended to be those with more behavioral difficulties, such that BMI was also associated with the shift in overall eating patterns.

CONCLUSIONS

Changes in behavioral function in seniors with AD result in a circadian shift in intake patterns with the preponderance of calories consumed at breakfast in those with increased behavioral difficulties. This shift in eating patterns associates both with poor overall intake and poor BMI.

Meal delivery practices do not meet needs of Alzheimer patients with increased cognitive and behavioral difficulties in a long-term care facility

BACKGROUND

Alterations in circadian rhythms and behavioral difficulties likely impact meal consumption patterns in elderly individuals with probable Alzheimer's disease (AD). Despite these known changes, the profile of meals provided in the institution parallels the needs of younger, free-living, healthy populations. This investigation examined the impact of food delivery patterns on achieved intakes in elderly individuals with probable AD in a long-term care facility and how this relationship changes depending on time of day, body weight status, behavioral function, and cognitive ability.

METHODS

Twenty-one consecutive days of investigator-weighed food intake and delivery collections were conducted on 25 elderly individuals with probable AD who maintained the ability to self-feed.

RESULTS

Energy consumed was positively associated with energy delivered for the majority of subjects, although the strength of this relationship varied across subjects and throughout the day. Energy delivered had the greatest impact on energy consumed at breakfast and the least impact at dinner in those with the greatest behavioral difficulties and cognitive impairment. Although those with low body mass indexes (BMIs) were likely to be delivered more energy, the impact of delivery on intakes decreased as energy delivered increased.

CONCLUSIONS

Delivering excess energy to patients with poor BMIs likely does not result in increased energy consumption. Behavioral and cognitive deterioration leads to a shift in the time of day that energy delivered has an impact on energy consumption, with the most progressed individuals being most impacted by foods delivered in the morning, suggesting that traditional meal practices are inappropriate for elderly individuals with AD.

Reassessment of the Ca2+ sensing property of a type I metabotropic glutamate receptor by simultaneous measurement of inositol 1,4,5-trisphosphate and Ca2+ in single cells

Transient transfection of Chinese hamster ovary or baby hamster kidney cells expressing the Group I metabotropic glutamate receptor mGlu1alpha with green fluorescent protein-tagged pleckstrin homology domain of phospholipase Cdelta1 allows real-time detection of inositol 1,4,5-trisphosphate. Loading with Fura-2 enables simultaneous measurement of intracellular Ca(2+) within the same cell. Using this technique we have studied the extracellular calcium sensing property of the mGlu1alpha receptor. Quisqualate, in extracellular medium containing 1.3 mm Ca(2+), increased inositol 1,4,5-trisphosphate in all cells. This followed a typical peak and plateau pattern and was paralleled by concurrent increases in intracellular Ca(2+) concentration. Under nominally Ca(2+)-free conditions similar initial peaks in inositol 1,4,5-trisphosphate and Ca(2+) concentration occurred with little change in either agonist potency or efficacy. However, sustained inositol 1,4,5-trisphosphate production was substantially reduced and the plateau in Ca(2+) concentration absent. Depletion of intracellular Ca(2+) stores using thapsigargin abolished quisqualate-induced increases in intracellular Ca(2+) and markedly reduced inositol 1,4,5-trisphosphate production. These data suggest that the mGlu1alpha receptor is not a calcium-sensing receptor because the initial response to agonist is not sensitive to extracellular Ca(2+) concentration. However, prolonged activation of phospholipase C requires extracellular Ca(2+), while the initial burst of activity is highly dependent on Ca(2+) mobilization from intracellular stores.

Single-cell imaging of graded Ins(1,4,5)P3 production following G-protein-coupled-receptor activation

The pleckstrin homology domain of phospholipase Cdelta1 (PH(PLCdelta)) binds Ins(1,4,5)P(3) and PtdIns(4,5)P(2) specifically, and can be used to detect changes in Ins(1,4,5)P(3) in single cells. A fusion construct of PH(PLCdelta) and enhanced green fluorescent protein (EGFP-PH(PLCdelta)) associates with the plasma membrane due to its association with PtdIns(4,5)P(2). However, PH(PLCdelta) has greater affinity for Ins(1,4,5)P(3) than PtdIns(4,5)P(2), and translocates to the cytosol as Ins(1,4,5)P(3) levels rise. Prolonged activation of group I metabotropic glutamate receptor 1alpha expressed in Chinese-hamster ovary cells or endogenous M(3) muscarinic receptors in SH-SY5Y neuroblastoma cells gave an initial transient peak in translocation, followed by a sustained plateau phase. This closely followed changes in cell population Ins(1,4,5)P(3) mass, but not PtdIns(4,5)P(2) levels, which decreased monophasically, as determined by radioreceptor assay. Translocation thus provides a real-time method to follow increases in Ins(1,4,5)P(3). Graded changes in Ins(1,4,5)P(3) in Chinese-hamster ovary-lac-mGlu1alpha cells could be detected with increasing glutamate concentrations, and dual loading with fura 2 and EGFP-PH(PLCdelta) showed that changes in intracellular Ca(2+) concentration closely paralleled Ins(1,4,5)P(3) production. Moreover, Ins(1,4,5)P(3) accumulation and intracellular Ca(2+) mobilization within single cells is graded in nature and dependent on both agonist concentration and receptor density.

Intracellular sphingosine 1-phosphate production: a novel pathway for Ca2+ release

Sphingolipids such as sphingosine 1-phosphate (SPP) and sphingosylphosphorylcholine have long been recognized to possess Ca2+ mobilizing activity, yet to date little is known about their mechanism of action, or indeed their significance as Ca2+ mobilizing intracellular messengers. The recent discovery of extracellular receptors for the sphingolipids has further complicated the interpretation of many experiments in this field. This paper reviews the current literature in which molecular and pharmacological approaches have begun to uncover the signalling components associated with intracellular SPP production and Ca2+ mobilization. The functional significance of this novel Ca2+ release pathway is also discussed.

Characterization of the metabotropic glutamate receptors mediating phospholipase C activation and calcium release in cerebellar granule cells: calcium-dependence of the phospholipase C response

In this study we have determined the metabotropic glutamate receptors (mGluRs) involved in the glutamate activation of phospholipase C (PLC) and Ca(2+) mobilization in cerebellar granule cells at 9 days in vitro; and studied the Ca(2+) modulation of the PLC response. Both PLC activation and Ca(2+) signalling were found to be mediated exclusively by the mGluR1 subtype, although both group I mGluRs, mGluR1 alpha and mGluR5, could be detected in cell extracts. Exposure of cells to medium devoid of Ca(2+) for various times before agonist stimulation reduced the PLC response, which was quickly recovered following the re-exposure of cells to Ca(2+)-containing medium. The extent of the glutamate response correlated well with changes in the cytosolic Ca(2+) concentration. On the other hand, loading of the intracellular Ca(2+) stores by a transient depolarization followed by washing in nondepolarizing buffer, allowed glutamate to release stored Ca(2+) in the majority of cells and enhanced glutamate activation of PLC. Under such conditions, the absence of extracellular Ca(2+) during stimulation and the chelation of cytosolic Ca(2+) with BAPTA/AM inhibited both glutamate-elicited Ca(2+) response and PLC activation. Overall, these results indicate that the mGluR-mediated activation of PLC depends on the presence of extracellular Ca(2+) and can be modulated by moderate changes of cytosolic Ca(2+). Furthermore, ryanodine reduced PLC stimulation by glutamate in predepolarized cells but not in control cells, suggesting that ryanodine receptors could play a role in the potentiation of the mGluR-mediated activation of PLC by Ca(2+) release in predepolarized cells.

Lysophosphatidic acid-induced Ca2+ mobilization requires intracellular sphingosine 1-phosphate production. Potential involvement of endogenous EDG-4 receptors

Lysophosphatidic acid (LPA)-mediated Ca(2+) mobilization in human SH-SY5Y neuroblastoma cells does not involve either inositol 1,4, 5-trisphosphate (Ins(1,4,5)P(3))- or ryanodine-receptor pathways, but is sensitive to inhibitors of sphingosine kinase. This present study identifies Edg-4 as the receptor subtype involved and investigates the presence of a Ca(2+) signaling cascade based upon the lipid second messenger molecule, sphingosine 1-phosphate. Both LPA and direct G-protein activation increase [(3)H]sphingosine 1-phosphate levels in SH-SY5Y cells. Measurements of (45)Ca(2+) release in premeabilized SH-SY5Y cells indicates that sphingosine 1-phosphate, sphingosine, and sphingosylphosphorylcholine, but not N-acetylsphingosine are capable of mobilizing intracellular Ca(2+). Furthermore, the effect of sphingosine was attenuated by the sphingosine kinase inhibitor dimethylsphingosine, or removal of ATP. Confocal microscopy demonstrated that LPA stimulated intracellular Ca(2+) "puffs," which resulted from an interaction between the sphingolipid Ca(2+) release pathway and Ins(1,4,5)P(3) receptors. Down-regulation of Ins(1,4,5)P(3) receptors uncovered a Ca(2+) response to LPA, which was manifest as a progressive increase in global cellular Ca(2+) with no discernible foci. We suggest that activation of an LPA-sensitive Edg-4 receptor solely utilizes the production of intracellular sphingosine 1-phosphate to stimulate Ca(2+) mobilization in SH-SY5Y cells. Unlike traditional Ca(2+) release processes, this novel pathway does not require the progressive recruitment of elementary Ca(2+) events.

Effect of dimethylsphingosine on muscarinic M(3) receptor signalling in SH-SY5Y cells

The sphingosine kinase inhibitor, dimethylsphingosine, is an important tool for investigating intracellular effects of the putative second messenger compound, sphingosine 1-phosphate. However, the specificity of action of dimethylsphingosine has not been fully investigated. In human SH-SY5Y neuroblastoma cells, dimethylsphingosine (30 microM), produced a 25-fold increase in the EC(50) for methacholine-induced Ca(2+) mobilisation, and reduced the maximum response by 57+/-5%, suggesting the involvement of sphingosine 1-phosphate production in the Ca(2+) signal. However, dimethylsphingosine also inhibited [3H]N-methylscopolamine binding to whole SH-SY5Y cells and reduced methacholine-induced phosphoinositide turnover. Thus, this compound must be used with caution when investigating the role of sphingosine kinase in G-protein coupled receptor-mediated Ca(2+) mobilisation responses.

Intracellular Ca2+ stores regulate muscarinic receptor stimulation of phospholipase C in cerebellar granule cells

Muscarinic receptor activation of phosphoinositide phospholipase C (PLC) has been examined in rat cerebellar granule cells under conditions that modify intracellular Ca2+ stores. Exposure of cells to medium devoid of Ca2+ for various times reduced carbachol stimulation of PLC with a substantial loss (88%) seen at 30 min. A progressive recovery of responses was observed following the reexposure of cells to Ca2+-containing medium (1.3 mM). However, these changes did not appear to result exclusively from changes in the cytosolic Ca2+ concentration ([Ca2+]i), which decreased to a lower steady level (approximately 25 nM decrease in 1-3 min after extracellular omission) and rapidly returned (within 1 min) to control values when extracellular Ca2+ was restored. Only after loading of the intracellular Ca2+ stores through a transient 1-min depolarization of cerebellar granule cells with 40 mM KCl, followed by washing in nondepolarizing buffer, was carbachol able to mobilize intracellular Ca2+. However, the same treatment resulted in an 80% enhancement of carbachol activation of PLC. In other experiments, partial depletion of the Ca2+ stores by pretreatment of cells with thapsigargin and caffeine resulted in an inhibition (18 and 52%, respectively) of the PLC response. Furthermore, chelation of cytosolic Ca2+ with BAPTA/AM did not influence muscarinic activation of PLC in either the control or predepolarized cells. These conditions, however, inhibited both the increase in [Ca2+]i and the PLC activation elicited by 40 mM KCl and abolished carbachol-induced intracellular Ca2+ release in predepolarized cells. Overall, these results suggest that muscarinic receptor activation of PLC in cerebellar granule cells can be modulated by changes in the loading state of the Ca2+ stores.

Lysophosphatidic acid-mediated Ca2+ mobilization in human SH-SY5Y neuroblastoma cells is independent of phosphoinositide signalling, but dependent on sphingosine kinase activation

Extracellular application of lysophosphatidic acid (LPA) elevated intracellular Ca(2+) concentration ([Ca(2+)](i)) in human SH-SY5Y neuroblastoma cells. The maximal response to LPA occurred between 0. 1 and 1 microM, at which point [Ca(2+)](i) was increased by approx. 500 nM. This increase was of similar magnitude to that caused by the muscarinic acetylcholine receptor agonist methacholine (MCh), although the initial rate of release by LPA was slower. Both LPA and MCh released Ca(2+) from intracellular stores, as assessed by inhibition of their effects by thapsigargin, a blocker of endoplasmic reticular Ca(2+) uptake, and by the persistence of their action in nominally Ca(2+)-free extracellular medium. Similarly, both agonists appeared to stimulate store-refilling Ca(2+) entry. MCh produced a marked elevation in cellular Ins(1,4,5)P(3) and stimulated [(3)H]InsP accumulation in the presence of Li(+). In contrast, LPA failed to stimulate detectable phosphoinositide turnover. Chronic down-regulation of Ins(1,4,5)P(3) receptor (InsP(3)R) proteins with MCh did not affect Ca(2+) responses to LPA. In addition, heparin, a competitive antagonist of InsP(3)Rs, blocked Ca(2+)-mobilization in permeabilized SH-SY5Y cells in response to MCh or exogenously added Ins(1,4,5)P(3), but failed to inhibit Ca(2+)-release induced by LPA. Elevation of [Ca(2+)](i) elicited by LPA was blocked by guanosine 5'-[beta-thio]-diphosphate, indicating that this agonist acts via a G-protein-coupled receptor. However, pertussis toxin was without effect on LPA-evoked [Ca(2+)](i) responses, suggesting that G(i/o)-proteins were not involved. In the absence of extracellular Ca(2+), N,N-dimethylsphingosine (DMS, 30 microM), a competitive inhibitor of sphingosine kinase, blocked LPA-induced Ca(2+) responses by almost 90%. In addition, MCh-induced Ca(2+) responses were also diminished by the addition of DMS, although to a lesser extent than with LPA. We conclude that LPA mobilizes intracellular Ca(2+)-stores in SH-SY5Y cells independently of the generation and action of Ins(1,4,5)P(3). Furthermore, the Ca(2+)-response to LPA appears to be dependent on sphingosine kinase activation and the potential generation of the putative second messenger sphingosine 1-phosphate.

Cross talk between m3-muscarinic and beta(2)-adrenergic receptors at the level of receptor phosphorylation and desensitization

In this study we investigated cross talk between m3-muscarinic and beta(2)-adrenergic receptors coexpressed in Chinese hamster ovary (CHO-m3/beta(2)) cells, focusing on two possible mechanisms of regulation. The first mechanism is based on recent in vitro studies demonstrating that G protein-coupled receptor kinase (GRK) activity, the protein kinase responsible for beta(2)-adrenergic receptor homologous phosphorylation and desensitization, may be regulated by calcium/calmodulin and membrane phosphatidylinositol 4, 5-bisphosphate. Stimulation of the phospholipase C signaling pathway via m3-muscarinic receptors in CHO-m3/beta(2) cells increased intracellular free calcium by approximately 10 fold and membrane phosphatidylinositol 4,5-bisphosphate levels decreased by approximately 74%. However, despite these changes the ability of endogenous kinases, possibly the GRKs, to phosphorylate the beta(2)-adrenergic receptor was not altered. The second mechanism investigated involves a direct heterologous phosphorylation of the beta(2)-adrenergic receptor after muscarinic receptor stimulation. Activation of m3-muscarinic receptors did mediate heterologous phosphorylation of beta(2)-adrenergic receptors in a GRK-independent fashion, via protein kinase C. Heterologous beta(2)-adrenergic receptor phosphorylation correlated with receptor desensitization as measured by a loss in guanine-nucleotide sensitive-high affinity agonist binding and reduction in maximal cAMP response. This receptor cross talk may have a profound physiological importance in a wide variety of cell types, for example smooth muscle, where these two receptors are known to be coexpressed.

Determination of the inositol (1,4,5) trisphosphate requirement for histamine- and substance P-induced Ca2+ mobilisation in human U373 MG astrocytoma cells

In human U373 MG astrocytoma cells, histamine and substance P stimulated similar peak increases in intracellular free calcium concentrations ([Ca2+]i), as measured by single cell imaging of Fura-2 fluorescence. Best-fit EC50 values for the peak Ca2+ response were 1.86 microM for histamine and 0.93 nM for substance P. The histamine Ca2+ response was manifest as either a series of repetitive spikes, or, at higher concentrations, a peak followed by a lower plateau level of Ca2+. In contrast, the substance P response became more transient at higher agonist concentrations. Substance P (10 nM) stimulated a biphasic increase in levels of inositol (1,4,5) trisphosphate (Ins(1,4,5)P3) with a peak of 97 +/- 5 pmoles/mg protein at 10 s. In contrast, the Ins(1,4,5)P3 response to 100 microM histamine was only marginally above basal levels of around 12 pmoles/mg protein. However, concentrations of histamine and substance P giving similar Ins(1,4,5)P3 responses produce similar peak increases in [Ca2+]i. HPLC analysis indicated that histamine stimulated the production of [3H]-Ins(1,4,5)P3 and its metabolites, although the magnitude of response was smaller than that observed with substance P. The initial Ca2+ responses to histamine and substance P did not require the presence of extracellular Ca2+. The Ca2+ response to histamine was unaffected by treatment with ryanodine, and was shifted to areas of lower agonist concentration by thimerosal. These results demonstrate that extremely small increases in Ins(1,4,5)P3 can stimulate large increases in [Ca2+]i in U373 MG cells, and suggest a marked redundancy for Ins(1,4,5)P3 production in the Ca2+ signalling pathway.

Effects of human type 1alpha metabotropic glutamate receptor expression level on phosphoinositide and Ca2+ signalling in an inducible cell expression system

Stable expression of the human type 1alpha metabotropic glutamate (mGlu 1alpha) receptor was achieved in Chinese hamster ovary cells using an isopropyl-beta-D-thiogalactoside (IPTG)-repressible expression system. Treatment of the cells with IPTG resulted in a time- and concentration-dependent induction of receptor expression. Maximal expression was obtained after treatment of the cells with 100 microM IPTG for 20 h, leading to a marked increase in receptor immunoreactivity detected by western blot, >30-fold stimulation of 3H-labelled inositol phosphate (3H-InsP) production, and a robust increase in intracellular calcium concentration in single cells after stimulation with 20 microM quisqualate. The basal level of 3H-InsP accumulation in cells induced with IPTG was increased by two- to threefold as compared with control cells; however, this basal activity was found to be dependent on glutamate released by the cells into the incubation medium. Following IPTG treatment, stable expression of the mGlu 1alpha receptor was maintained for at least 1 week. Taken together, these results clearly indicate the advantages of working with an inducible expression system when studying the biochemical and pharmacological properties of the human mGlu 1alpha receptor in transfected cells.

Dual effects of histamine and substance P on intracellular calcium levels in human U373 MG astrocytoma cells: role of protein kinase C

1. In human U373 MG astrocytoma cells agonist-induced increases in intracellular Ca2+ ([Ca2+]i) are rapidly returned towards prestimulated levels. Examination of the effect of histamine and substance P on [Ca2+]i in thapsigargin-treated cells has allowed a mechanism contributing to this effect to be characterized. 2. Histamine and substance P stimulated [3H]-inositol monophosphate ([3H]-IP1) accumulation in U373 MG cells. Concentration-response curves of [3H]-IP1 accumulation in suspensions of U373 MG cells in HEPES buffer containing 30 mM Li+ yielded best-fit EC50 values of 19.1+/-1.5 microM for histamine and 5.7+/-1.3 nM for substance P. 3. In confluent monolayers of fura-2 loaded U373 MG cells perfusion with 100 microM histamine resulted in a transient 597+/-50 nM increase in [Ca2+]i. The best-fit EC50 for histamine was 4.6+/-2.2 microM. The initial, transient, histamine response was often followed by further small transient increases in [Ca2+]i. 4. Treatment of U373 MG cells with 5 microM thapsigargin, followed by the readdition of 1.8 mM Ca2+ to the perfusion buffer, resulted in a steady-state level of [Ca2+]i 97+/-5 nM above pretreated levels (measured 400 s after readdition of Ca2+). Perfusion of histamine (100 microM, 100 s) caused a rapid decline in the thapsigargin-induced steady state level of [Ca2+]i. This effect of histamine was normally reversible upon washout. The best-fit EC50, for the histamine response was 0.8+/-0.2 microM. Substance P (10 nM, 100s) also caused a reduction in thapsigargin-induced steady-state levels of [Ca2+]i. 5. Neither 100 microM histamine nor 10 nM substance P inhibited the rate of quench of fura-2 fluorescence by Mn2+ in U373 MG cells pretreated with 5 microM thapsigargin, indicating that the depressant effect on steady-state raised [Ca2+]i was probably not due to a block of Ca2+ entry. 6. The depressant effect of histamine on [Ca2+]i was blocked by 1 microM mepyramine, and was partially reduced by pre-incubation with 1 microM staurosporine (61+/-7% reduction) and with Ro 31-8220 (24+/-10% and 50+/-6% reduction by 1 and 10 microM Ro 31-8220, respectively). Pre-incubation with H-89 did not alter the depressant effect of histamine. 7. Neither 1 microM staurosporine nor 10 microM KN-62 inhibited the binding of [3H]-mepyramine to guinea-pig cerebellar membranes, whereas it was reduced by 17+/-1% and 55+/-2% by 1 and 10 microM Ro 31-8220, respectively. However, [3H]-IP1 accumulation stimulated by histamine in U373 MG cells was not inhibited by 1 or 10 microM Ro 31-8220 and in 2 out of 3 experiments there was a significant potentiation of the response to histamine with both concentrations of Ro 31-8220. Staurosporine, 1 microM, similarly potentiated the response to 100 microM histamine in 3 out of 4 experiments. KN-62 (10 microM) did not stimulate histamine-induced [3H]-IP1 accumulation. 8. In HEPES buffer to which no Ca2+ had been added, histamine stimulated a transient 451+/-107 nM increase in [Ca2+]i. Pretreatment with 1 microM and 10 microM Ro 31-8220 did not significantly alter the initial peak response to histamine, but slowed the rate at which histamine-induced increases in [Ca2+]i were returned to prestimulated levels. Pretreatment with KN-62 had no significant effect on the response to histamine, but consistently inhibited the secondary slower phase of the decline in [Ca2+]i. H-89 did not alter the histamine response. 9. The effect of histamine in stimulating Ca2+ extrusion was not confined to U373 MG cells, since 100 microM histamine also caused a rapid decrease in steady-state levels of [Ca2+]i in thapsigargin-treated human HeLa cells. 10. The results indicate that agonists which increase [Ca2+]i via activation of phosphoinositide metabolism can also stimulate a homeostatic mechanism which acts to reduce [Ca2+]i. The balance of the evidence indicates that in U373 MG cells the latter effect most likely involves a PKC-mediated stimulation of a Ca2+-extrusion pump.

Extracellular calcium concentration controls the frequency of intracellular calcium spiking independently of inositol 1,4,5-trisphosphate production in HeLa cells

Stimulation of single HeLa cells with histamine evoked repetitive increases of the intracellular calcium ion concentration (Ca2+ spikes). The frequency of Ca2+ spiking increased as the extracellular hormone concentration was elevated. In addition, the frequency of Ca2+ spiking could be accelerated by increasing the extracellular Ca2+ concentration ([Ca2+]0) in the presence of a constant hormone concentration. The range of [Ca2+]0 over which the spiking frequency could be titrated was nominally-zero to 10mM, being half-maximally effective at approx. 1 and 2.5mM for 37 and 22 degrees C respectively. The effect of [Ca2+]0 on inositol phosphates production was also examined. Changes of [Ca2+]0 over a range which had been found to affect the frequency of Ca2+ spiking did not have any effect on the rate of myo-inositol 1,4,5-trisphosphate (InsP3) production, although an increase in inositol phosphates production was observed as [Ca2+]0 was increased from zero to values giving less than half-maximal Ca2+ spike frequency. These data suggest that at low Ca2+ spike frequency, Ca2+-stimulated activation of phospholipase C may contribute to Ca2+ spiking in HeLa cells, but under some conditions the availability of Ca2+ to the intracellular stores, rather than changes in the rate of InsP3 production, determines the Ca2+ spike frequency.

Potentiation by 1,4-dithiothreitol of histamine-induced inositol phosphate formation in rat cerebral cortex and human HeLa cells

Dithiothreitol (1 mM) caused a 340-fold shift of the concentration-response curve for histamine-induced [3H]inositol monophosphate ([3H]IP1) accumulation in slices of rat cerebral cortex prelabelled with [3H]inositol. Dithiothreitol had no significant effect on carbachol-induced [3H]IP1 accumulation. The effect of dithiothreitol appeared to be at the level of the H1-receptor, since curves of histamine inhibition of [3H]mepyramine binding to a membrane fraction from rat cerebral cortex were shifted to lower concentrations by dithiothreitol, with a similar concentration-dependence for dithiothreitol as observed for potentiation of [3H]IP1 accumulation. The small shift of the curve of histamine inhibition of [3H]mepyramine binding by a stable GTP analogue, 5'-guanylylimidodiphosphate, was not increased in the presence of dithiothreitol. Histamine-induced [3H]IP1 accumulation in human HeLa cells was also potentiated by dithiothreitol, but the decrease in the EC50 was only 3-fold. It is suggested that differences in the magnitude of the effect of dithiothreitol on histamine H1-receptor mediated responses between tissues may reflect in part the position of the concentration-response curve in the absence of dithiothreitol.

EXPERIMENTS ON THE PHOTOLYSIS OF AQUEOUS SOLUTIONS OF CHLORINE, HYPOCHLOROUS ACID, AND SODIUM HYPOCHLORITE

The photodecompositions of aqueous solutions of chlorine, hypochlorous acid, and sodium hypochlorite have been studied under a variety of conditions involving a wide range of pH, with particular attention paid to the quantum efficiency and to the proportions of the products. Reaction schemes are suggested to account for the results.