Differential effect of temperature on histamine- and carbachol-stimulated inositol phospholipid breakdown in slices of guinea-pig cerebral cortex

Phospholipid metabolism in an industry microalga Chlorella sorokiniana: the impact of inoculum sizes

Chlorella sorokiniana is an important industry microalga potential for biofuel production. Inoculum size is one of the important factors in algal large-scale culture, and has great effects on the growth, lipid accumulation and metabolism of microalgae. As the first barrier of cell contents, membrane plays a vital role in algal inoculum-related metabolism. The knowledge of phospholipids, the main membrane component and high accumulation of phospholipids as the major content of total lipids mass in some microalgae, is necessary to understand the role of membrane in cell growth and metabolism under different inoculum density. Profiling of C. sorokiniana phospholipids with LC-MS led to the identification of 119 phospholipid species. To discover the phospholipid molecules most related to change of inoculum sizes, Partial Least Squares Discriminant Analysis (PLS-DA) was employed and the results revealed that inoculum sizes significantly affected phospholipid profiling. Phosphatidylglycerol (PG), phosphatidyl- ethanolamine (PE) and several phosphatidylcholine (PC) species might play an important role under our experimental conditions. Further analysis of these biomarkers indicated that cell membrane status of C. sorokiniana might play an important role in the adaption to the inoculum sizes. And the culture with inoculum size of 1×10⁶ cells mL⁻¹ presented the best membrane status with the highest content of PC and PG, and the lowest content of PE. We discovered that the inoculum size of 1×10⁶ cells mL⁻¹ might provide the best growth condition for C. sorokiniana. Also we proposed that PG, PE and several PC may play an important role in inoculum-related metabolism in C. sorokiniana, which may work through thylakoid membrane and photosynthetic pathway. Thus this study would provide more potential targets for metabolic engineering to improve biofuel production and productivity in microalgae.

Potentiation and suppression of the histamine response by raising and lowering the temperature in canine visceral polymodal receptors in vitro

It is well known that itch and inflammatory pain are enhanced when tissue is warmed, while they are suppressed when tissue is cooled. To see whether these changed sensations are based on the changed response of sensory receptors, the temperature dependency of the excitation of polymodal receptors induced by histamine, which plays an important role both in itch and inflammatory pain, was studied. Single nerve activities of polymodal receptors were recorded from canine testis-spermatic nerve preparations in vitro. Raising the temperature from 34 to 40 degrees C, a temperature below the threshold for the heat response of polymodal receptors, facilitated the histamine-induced nerve discharge to 268% of that at 34 degrees C, while lowering the temperature to 28 degrees C decreased it to 25%. Facilitation of the histamine response was also observed in the noxious temperature range (48 and 51 degrees C). These results suggest that the potentiation of the histamine-induced sensation by increasing the tissue temperature, as well as its suppression by lowering tissue temperature, can be explained by a temperature-dependent response of peripheral sensory receptors to histamine. However, the suppression of itch by noxious heat reported by Bickford (Bickford, R.G., Experiments relating to the itch sensation, its peripheral mechanism, and central pathways, Clin. Sci. Incorp. Heart, 3 (1937) 377-386) cannot be explained by the noxious heat-induced facilitation of the peripheral receptor response reported in this paper.

Effects of hypomagnesia on histamine H1 receptor-mediated facilitation of NMDA responses

1. The ability of histamine to facilitate the N-methyl-D-aspartate (NMDA) induced depolarization of cortical projection neurones was examined by use of grease-gap recording. 2. Histamine (1 to 15 microM) reversibly facilitated the NMDA-induced depolarization yielding a bellshaped concentration-response relationship. The peak enhancement was 167% above the control at 10 microM histamine. Desensitization was present in 4 out of 5 slices on second exposure 40 min following the first exposure. 3. Histamine did not alter the depolarization induced by 10 microM kainate. 4. The histamine-induced facilitation persisted in the presence of tetrodotoxin, but was reduced in a concentration-dependent manner by diphenhydramine (IC50 = 7.6 nM). Cyproheptadine (10 nM) also reduced the facilitation, whereas ranitidine (200 nM) and thioperamide (10 nM) were ineffective in this regard. 5. Histamine (10 microM) facilitated the NMDA (25 microM)-induced depolarization in nominally Mg(2+)-free medium. The magnitude of the facilitation was smaller than that observed in Mg(2+)-containing medium (17% above the control) and desensitization was not observed. This facilitation was not reduced by cyproheptadine (10 nM) or diphenhydramine (1 microM). 6. We conclude that histamine facilitates the NMDA depolarization at cortical neurones via two distinct mechanisms. One mechanism involves activation of the histamine H1 receptor and is sensitive to Mg2+. The second mechanism is independent of histamine cell surface receptor activation and may reflect a direct action of histamine at the NMDA receptor.

Differential effects of elevated calcium ion concentrations on inositol phospholipid responses in mouse and rat cerebral cortical slices

Inositol phospholipid turnover in cerebral cortical slices from mouse and rat was assessed using a [3H]inositol pre-labelling technique followed by anion exchange chromatography to isolate [3H]inositol phosphates ([3H]InsP chi). In both mouse and rat cerebral cortical slices, elevating the CaCl2 concentration of the Krebs medium from 1.3 to 4 mM did not significantly enhance the accumulation of [3H]InsP chi in the absence of any stimulus, or in the presence of glutamate (3 mM), depolarizing concentrations of KCl (25 mM), 5-hydroxytryptamine (0.3 mM), the calcium ionophore A23187 (33 microM) or carbachol (1 mM). However, the accumulations of [3H]InsP chi induced by histamine (1 mM) or noradrenaline (0.1 mM) were significantly increased by between 95 and 178% in cerebral cortical slices from both species by the elevation of extracellular calcium. Analysis of the individual inositol phosphates revealed that elevated ambient calcium enhanced the histamine-generated accumulations of [3H]InsP2, [3H]InsP3 and [3H]InsP4 by up to two-fold, while only the [3H]InsP3 response to carbachol was significantly increased. Under the same conditions, histamine, but not carbachol, selectively increased the accumulation of [3H]PtdInsP2 by up to 50%. The [3H]InsP chi responses to histamine and noradrenaline in combination with the calcium ionophore A23187 were greater-than-additive, inferring an enhancement of the receptor response by raised intracellular calcium. However, the combination of A23187 with glutamate or KCl resulted in significantly less-than-additive [3H]InsP chi responses. The [3H]InsP chi response to carbachol or 5-hydroxytryptamine was not significantly altered in the presence of A23187. Taken together, these results indicate heterogeneity between the mechanisms of inositol phospholipid turnover induced by these various stimuli in mammalian cerebral cortical slices.

gamma-Aminobutyric acid inhibition of histamine-induced inositol phosphate formation in guinea-pig cerebellum: comparison with guinea-pig and rat cerebral cortex

1. gamma-Aminobutyric acid (GABA), 2 mM, inhibited basal accumulation of [3H]-inositol monophosphate ([3H]-IP1) in lithium-treated slices of guinea-pig cerebellum preincubated with [3H]-inositol. In contrast, 2 mM GABA stimulated the accumulation of [3H]-IP1 in rat cerebral cortical slices over a 60 min incubation period, but had no significant effect in slices of guinea-pig cerebral cortex. The estimated IC50 for the inhibitory action of GABA in guinea-pig cerebellar slices was 0.52 +/- 0.12 mM. 2. GABA inhibited histamine-induced [3H]-IP1 accumulation in guinea-pig cerebellar slices in a non-competitive manner. The best-fit value for the maximum level of inhibition was 74 +/- 6%. The estimated IC50 for GABA was 0.77 +/- 0.15 mM and was not significantly different from the IC50 for inhibition of the basal accumulation of [3H]-IP1. The response to histamine in guinea-pig and rat cerebral cortical slices was also inhibited by 2 mM GABA. 3. In guinea-pig cerebellar slices 2 mM GABA potentiated histamine-induced [3H]-inositol bisphosphate ([3H]-IP2) accumulation, whereas in both guinea-pig and rat cerebral cortex the effect was inhibition. 4. Isoguvacine and muscimol, GABAA-selective agonists, and (-)-baclofen, GABA(B)-selective, had no significant effect on basal or histamine-stimulated accumulation of [3H]-IPs in guinea-pig cerebellar slices. (-)-Baclofen had only a weak inhibitory effect on [3H]-IP1 accumulation in guinea-pig-cerebral cortex (16 +/- 6% inhibition with 10 microM (-)-baclofen), whereas in rat cerebral cortex (-)-baclofen mimicked the inhibitory effect of GABA. 5. Nipecotic acid (1 mM) had qualitatively similar effects to those of 2mm GABA in guinea-pig cerebellar slices. 6. The competitive GABA uptake inhibitors SK&F 89976-A, SK&F 100330-A and SK&F 100561-A were potent histamine H,-receptor antagonists, as indicated by the inhibition of [3H]-mepyramine binding to homogenates of guinea-pig cerebellum and cerebral cortex. 7. GABA (2 mM) caused a small inhibition (12 + 3%) of [3H]-inositol incorporation into total inositol phospholipids in guinea-pig cerebellar slices, as in rat cerebral cortical slices, whereas 0.2mm histamine caused a small stimulation (15 + 4%). In the presence of both GABA and histamine, [3H]-inositol incorporation was unchanged from basal (101 + 5%). 8. GABA also inhibited [3H]-IP1 formation induced by endothelin-1 in guinea-pig cerebellar slices and increased, but not significantly, the amount of [3H]-IP2 accumulated. This, taken with the inhibitory effect on basal and histamine-stimulated accumulation, suggests that the action of GABA in guinea-pig cerebellar slices may be non-selective and may not be exerted through a specific GABA receptor.

Discriminatory effects of forskolin and EGTA on the indirect cyclic AMP responses to histamine, noradrenaline, 5-hydroxytryptamine, and glutamate in guinea-pig cerebral cortical slices

The effects of forskolin (1 microM) and EGTA (5 mM) on indirect cyclic AMP responses in slices of guinea-pig cerebral cortex were examined. Forskolin had little effect on the direct 2-chloroadenosine-stimulated cyclic AMP response. However, it completely abolished the glutamate-induced augmentation of this response. In contrast, forskolin had very little effect on the indirect cyclic AMP responses to noradrenaline, 5-hydroxytryptamine, and histamine. Conversely, rapid removal of extracellular calcium with EGTA 2 min before addition of the indirectly acting agent markedly reduced the augmentation responses produced by these latter agonists, but had little effect on the glutamate augmentation. When EGTA was added once a steady level of cyclic AMP had been achieved with the indirect agents, it was without effect on any of the responses. Thus, calcium appears to have a role in the early, but not the later, stages of the noradrenaline, 5-hydroxytryptamine, and histamine responses. A role for protein kinase C in the glutamate augmentation response was suggested, because forskolin inhibited the augmentation of the 2-chloroadenosine response produced by phorbol esters (which mimic the actions of diacylglycerol in activating protein kinase C). We conclude that there is more than one mechanism by which the augmentation of cyclic AMP responses can occur.

Beta-adrenoceptor stimulation inhibits histamine-stimulated inositol phospholipid hydrolysis in bovine tracheal smooth muscle

1. Histamine and carbachol produced concentration-related increases in the accumulation of 3H-inositol phosphates in slices of bovine tracheal smooth muscle. 2. Noradrenaline alone produced a small stimulation of 3H-inositol phosphate accumulation which was inhibited by the alpha-adrenoceptor antagonist phentolamine. In contrast, when noradrenaline (0.1 mM) was added simultaneously with histamine it significantly reduced the inositol phosphate response to high (greater than or equal to 0.1 mM) concentrations of histamine. However, noradrenaline had no inhibitory effect on the carbachol-induced inositol phosphate response. 3. The non-selective beta-agonist isoprenaline (IC50 = 0.08 microM) and the beta 2-selective agonist salbutamol (IC50 = 0.29 microM) both produced a dose-related inhibition of the inositol phosphate response to 0.1 mM histamine. The inhibitory effect of salbutamol was antagonized by propranolol (KA = 2.4 x 10(9) M-1) and the beta 2-selective adrenoceptor antagonist ICI 118551 (KA = 1.7 x 10(9) M-1). 4. The accumulation of 3H-inositol phosphates induced by histamine increased steadily over a 40 min period after an initial lag period of 3-4 min. Following the simultaneous addition of histamine and salbutamol there was a further delay of 3-4 min before the appearance of the inhibitory effect of salbutamol. 5. The effect of histamine on inositol phosphate accumulation was accompanied by a stimulation of [3H]-inositol incorporation into membrane phospholipids which was reduced by the presence of salbutamol. However, when histamine was used to stimulate maximally [3H]-inositol incorporation during the prelabelling period, salbutamol produced a marked inhibition of histamine-stimulated 3H-inositol phosphate accumulation under conditions in which there was no change in the level of incorporation.

GABAB receptor-mediated inhibition of histamine H1-receptor-induced inositol phosphate formation in slices of rat cerebral cortex

Histamine-stimulated accumulation of [3H]inositol monophosphate ([3H]IP1) in lithium-treated slices of rat cerebral cortex was inhibited by gamma-aminobutyric acid (GABA) (IC50 0.30 +/- 0.03 mM). The maximum level of inhibition was 69 +/- 2%. GABA alone caused a small stimulation of basal accumulation of [3H]IP1. The inhibitory action of GABA on the response to histamine was mimicked by the GABAB agonist (-)-baclofen, IC50 0.69 +/- 0.04 microM, which was 430-fold more potent as an inhibitor than the (+)-isomer. (-)-Baclofen also inhibited histamine-induced formation of [3H]inositol bisphosphate ([3H]IP2) and [3H] inositol trisphosphate ([3H]IP3). Inhibition curves for GABA and for (-)-and and (+)-baclofen had Hill coefficients greater than unity. (-)-Baclofen, at concentrations that caused inhibition of histamine-induced [3H]IP1 accumulation, did not alter the basal level of [3H]IP1 or the incorporation of [3H]inositol into total inositol phospholipids. Isoguvacine, a GABAA agonist, had no effect on either the histamine-stimulated or basal accumulation of [3H]IP1. GABA had no effect on carbachol-stimulated [3H]IP1 formation.

Histamine H1-receptors mediate phosphoinositide hydrolysis in astrocyte-enriched primary cultures

Astrocyte-enriched primary cultures of newborn rat brain hemispheres, prelabeled with [3H]inositol, accumulated [3H]inositol phosphate but not [3H]inositol bis- and tris-phosphate, after exposure to histamine for 60 min in the presence of 10 mM LiCl. The response to histamine was not a function of contaminating meningeal fibroblasts since no accumulation of [3H]inositol phosphate was elicited by histamine in meningeal cultures. The stimulation of phosphoinositide hydrolysis by histamine in astrocytes was dose-dependent (EC50 = 1.7 microM, maximal effect = 345% over basal levels) and was mimicked by several H1-receptor agonists. The use of selective receptor antagonists confirmed that the histamine response was the result of activation of H1-receptors. The histamine-induced [3H]inositol phosphate accumulation was completely abolished by omission of Ca2+ from the incubation medium. Astrocyte membranes specifically bound the radiolabeled H1-antagonist, [3H]mepyramine with an affinity (Kd = 5.9 nM) and a density of binding sites (Bmax = 113 fmol/mg protein) similar to rat brain. These results demonstrate the presence of functional histamine H1-receptors in rat brain astrocytes and suggest a role for histamine as a neuromodulator of astrocyte function.

Deamination of methylamine by semicarbazide-sensitive amine oxidase in human umbilical artery and rat aorta

The deamination of methylamine (MA) by amine oxidase enzymes has been studied and compared with that of benzylamine (BZ) in homogenates of rat aorta and human umbilical artery by means of a radiochemical assay to estimate the radiolabelled deaminated metabolites produced, and also a spectrophotometric assay to measure H2O2 formation during the metabolism of these substrates. The effects of various inhibitors used in these assays suggest that a semicarbazide-sensitive amine oxidase (SSAO) is predominantly if not wholly responsible for the deamination of both MA and BZ in these tissues. MA was found to have a relatively higher apparent Km (102 microM in aorta; 779 microM in umbilical artery) than BZ (6.8 microM in aorta; 207 microM in umbilical artery) for metabolism by SSAO in these tissues. However, these large differences between species in the apparent Km values for each amine indicate that the biochemical properties of SSAO in human and rat vasculature are not identical. SSAO in human umbilical artery was particularly active towards MA, with a Vmax which was approximately 70% greater than that for BZ as substrate, whereas in rat aorta the Vmax for MA was around 60% of that for BZ. MA is known to occur endogenously in man and other species, and the possibility that it may be a physiological substrate in vivo for SSAO is discussed.