On the role of agonist-evoked Ca2+ mobilization in sustaining the ongoing phosphoinositide hydrolysis

Stimulation of SK-N-BE(2) cells with 1 mM carbachol (Cch) elicited phosphoinositide (PPI) hydrolysis and a rapid elevation of cytosolic Ca²⁺ concentration ([Ca²⁺]_i) from 115 nM to about 500 nM, followed by a plateau around 200 nM. In myo [³H]inositol-labelled cells, Cch-evoked accumulation of [³H]inositol phosphates (IPs) was not affected when [Ca²⁺]_i was clamped at resting by cell loading with 10 M BAPTA/AM; under these conditions, maximal 1,4,5-inositol trisphosphate accumulation was not reduced either. When [Ca²⁺]_i was clamped around 700 nM by cell treatment with 600 nM ionomycin, Cch-evoked [³H]IPs accumulation was enhanced by less than 20%, but it was impaired by a 30% and a 55% after [Ca²⁺]_i reduction to about 70 nM and 35—50 nM, by cell loading with 20 M or 40 M BAPTA/AM, respectively. These results show that, in SK-N-BE(2) cells, Cch-activated PPI-specific phospholipase C is sensitive to [Ca²⁺]_i but it already operates under suboptimal conditions at resting [Ca²⁺]_i.     

In vivo intrahippocampal microinfusion of carbachol and bicuculline induces theta-like oscillations in the septally deafferented hippocampus.

In their laboratory the authors have previously demonstrated that hippocampal slices could be induced to generate trains of "theta-like" oscillations by whole-bath perfusions of carbachol. Until recently, it has not been possible to generate similar activity in the septally deafferented hippocampus of an otherwise intact brain by microinfusions of carbachol. This study presents a full report of the first demonstration of a theta-like oscillation in the in vivo, septally deafferented hippocampal formation. Rats were anesthetized with urethane and implanted with microinfusion cannulae in the region of the medial septum/vertical limb of the diagonal band of Broca (MS/vDBB) and at single or multiple sites in the stratum moleculare of the fascia dentata. The MS/vDBB was microinfused with procaine hydrochloride to produce a reversible suppression lasting for approximately 20 minutes. Intrahippocampal microinfusions of carbachol or bicuculline alone (in the postprocaine condition of the MS/vDBB) failed to produce any theta-like oscillations. The combination of carbachol and bicuculline produced trains of theta-like oscillations during suppression of the MS/vDBB very similar to those seen in the slice preparations. The oscillations were blocked by intravenous administration of atropine sulfate, and they had the same depth profile as that of theta. Theta-on cells were shown to discharge in rhythmic bursts in synchrony with the oscillations. Thus, it would appear that the essential nature of the medial septal input to the hippocampal formation, for the generation of theta field activity in the intact brain, consists of a critical balance between cholinergic and GABAergic circuitry.     

氨甲酰胆碱和毛果芸香碱对血管内皮细胞M受体基因表达的调节作用

目的：比较氨甲酰胆碱和毛果芸香碱对血管内皮细胞M受体基因表达调节作用的异同点。方法：氨甲酰胆碱和毛果芸香碱分别孵育培养的牛主动脉内皮细胞10h后，提取细胞总RNA，RT-PCR方法测定M受体5个亚型mRNA的表达。结果：M_1～M_5受体mRNA在牛主动脉内皮细胞上均有表达，氨甲酰胆碱和毛果芸香碱孵育后表达量均增加，但二者之间无差异。结论：氨甲酰胆碱和毛果芸香碱对M受体5个亚型的基因表达均发生了相同的影响，两者对M受体可能的作用尚不能解释其对血管张力的影响。     

Inhibition of carbachol stimulated acid secretion by interleukin 1beta in rabbit parietal cells requires protein kinase C

BACKGROUND: Interleukin 1beta (IL-1beta) is a potent inhibitor of gastric acid secretion. Regulatory actions at several levels have previously been demonstrated, including direct inhibition of parietal cell acid secretion. Although IL-1beta may activate several intracellular signalling pathways, the mechanisms responsible for inhibition of carbachol stimulated acid secretion have not been determined. AIMS: To investigate the roles of protein kinase C (PKC) and the sphingomyelinase signalling pathways in the regulation of acid secretion by IL-1beta. METHODS: Rabbit parietal cells were obtained by collagenase-EDTA digestion and centrifugal elutriation. Acid secretion stimulated by carbachol and A23187 (to mimic elevations in intracellular calcium) was assessed by 14C aminopyrine uptake in response to IL-1beta, PKC, and sphingomyelinase manipulation. RESULTS: IL-1beta inhibited carbachol and A23187 stimulated acid secretion in a dose dependent manner. The inhibitory actions were completely reversed by each of three different PKC inhibitors, staurosporine, H-7, and chelerythrine, as well as by PKC depletion with high dose phorbol ester pretreatment. IL-1beta did not downregulate parietal cell muscarinic receptor. IL-1beta significantly increased membrane PKC activity. Activation of the sphingomyelinase/ceramide pathway had no effect on basal or stimulated acid secretion. The inhibitory action of IL-1beta was independent of protein kinase A and protein kinase G activity. CONCLUSIONS: IL-1beta directly inhibits parietal cell carbachol stimulated acid secretion. This action occurs distal to muscarinic receptor activation and elevations in intracellular calcium and requires PKC.     

Labrasol® and Salts of Medium-Chain Fatty Acids Can Be Combined in Low Concentrations to Increase the Permeability of a Macromolecule Marker Across Isolated Rat Intestinal Mucosae

In addition to their solubilizing properties, excipients used in lipid-based formulations can improve intestinal permeability of macromolecules. We determined whether admixing of medium-chain fatty acid (MCFA) permeation enhancers with a lipoidal excipient (Labrasol^®) could potentiate transepithelial flux of a poorly permeable macromolecule (fluorescein isothiocyanate dextran 4 kDa [FD4]) across rat intestinal mucosae mounted in Ussing chambers. Low concentrations of sodium caprate (C₁₀), sodium undecylenate (C_11:1), or sodium laurate (C₁₂) combined with Labrasol^® increased the apparent permeability coefficient (P_app) of FD4 to values typically seen with higher concentrations of MCFAs or Labrasol^® alone. For example, combination of C_11:1 (0.5 mg/mL) with Labrasol^® (1 mg/mL) increased the P_app of FD4 by 10- and 11-fold over the respective individual agents at the same concentrations where no enhancement was evident. The increased enhancement ratios seen with the combinations were associated with some perturbation in intestinal histology and with attenuation of an epithelial functional measure, carbachol-stimulated inward short-circuit current. In conclusion, combining three MCFAs separately with Labrasol^® increased the P_app of FD4 to values greater than those seen for MCFAs or Labrasol^® alone. Ultimately, this may permit lower concentrations of MCFA to be used in combination with other excipients in oral formulations of poorly permeable molecules.     

Age-dependent contribution of Rho kinase in carbachol-induced contraction of human detrusor smooth muscle in vitro

Aim： Activation of muscarinic receptors on the detrusor smooth muscle is followed by contraction, which involves both myosin light chain kinase （MLCK） and Rho kinase （ROCK）. The aim of this study was to determine the relative contributions of MLCK and ROCK to carbachol-induced contraction of human detrusor smooth muscle in vitro.
Methods： Detrusor smooth muscle strips were prepared from the macroscopically unaffected bladder wall of patients underwent cystectomy. The strips were fixed in an organ bath, and carbachol or KCl-induced isometric contractions were measured by force transducers.

Results： Addition of carbachol （0.4-4 μmol/L） into the bath induced concentration-dependent contractions of detrusor specimens, which was completely abolished by atropine （1 μmol/L）. Pre-incubation of detrusor specimens with either the MLCK inhibitor ML-9 or the ROCK inhibitors HA1100 and Y-27632 （each at 10 μmol/L） significantly blocked carbachol-induced contractions as compared to the time-control experiments. Moreover, MLCK and ROCK inhibition were equally effective in reducing carbachol-induced contractions. The residual carbachol-induced contractions in the presence of both MLCK and ROCK inhibitors were significantly smaller than the contractions obtained when only one enzyme （either MLCK or ROCK） was inhibited, suggesting an additive effect of the two kinases. Interestingly, ROCK-mediated carbachol-induced contractions were positively correlated to the age of patients （r=0.52, P〈0.05）.

Conclusion： Both MLCK and ROCK contribute to carbachol-induced contractions of human detrusor smooth muscle. ROCK inhibitors may be a new pharmacological approach to modulate human bladder hyperactivity.     

兴奋胆碱能通路对内毒素血症和肠缺血/再灌注动物肝脏功能的保护作用

目的:观察不同方式激活胆碱能受体途径对内毒素血症和肠缺血/再灌注动物肝脏功能的保护作用.方法:静脉注射内毒素(LPS,10 mg/kg和5 mg/kg)复制大鼠内毒素血症模型(每组10只),肠系膜上动脉夹闭1 h后松夹复制肠缺血/再灌注模型(每组6只),兔肠系膜上动脉部分阻断后4 h恢复血流复制兔肠部分缺血/再灌注模型(每组5只).内毒素血症大鼠分别施与迷走神经刺激或电针副交感神经相关穴位(后三里穴),并分别设模型组、假手术组和迷走神经切断组或电针假穴组;肠缺血/再灌注动物经肠袋(距离回盲部15 cm处起始,向空肠端作一个长约10 cm肠袋,保留血液供应)给予卡巴胆碱(大鼠:0.1 mg/kg;兔:3μg/kg),并设假手术组和模型组.各组大鼠于实验结束时、各组兔于上动脉阻断0、2、4、6、8 h及1、2、3 d取股动脉血测定血浆丙氨酸转氨酶(ALT)活性.结果:与模型组、迷走神经切断组或电针假穴组比较,采用迷走神经刺激或电针刺激副交感神经相关穴位(后三里穴)明显降低内毒素血症大鼠早期血浆ALT活性(P＜0.05或P＜0.01);肠缺血及再灌注后大鼠ALT明显升高,肠袋给予卡巴胆碱后ALT水平均有明显改善.肠袋输注卡巴胆碱兔血浆ALT活性在缺血/再灌注早期较缺血前增加,再灌注后逐渐恢复,伤后3 d基本接近正常水平,而模型组则逐渐升高.结论:通过刺激副交感神经或局部给予拟胆碱药的方式激活胆碱能受体途径对内毒素血症和肠缺血/再灌注动物肝脏功能具有不同程度的保护作用.     

Epidermal growth factor partially restores colonic ion transport responses in mouse models of chronic colitis

BACKGROUND & AIMS: Epidermal growth factor receptor (EGFR) activation, which plays an important role in regulating intestinal ion transport, can alleviate clinical symptoms such as diarrhea in patients with ulcerative colitis and promote mucosal restitution in animal models of colitis. Here, we investigate whether EGFR can regulate colonic ion transport in the setting of colitis. METHODS: Distal colon from control mice and mice with colitis was retained for immunohistochemistry or mounted in Ussing chambers. Ion transport responses across the tissues to the calcium agonist carbachol and the adenosine 3',5'-cyclic monophosphate agonist forskolin were measured with or without epidermal growth factor (EGF) pretreatment. RESULTS: EGF pretreatment of normal colonic mucosa inhibited ion transport responses to carbachol and forskolin but potentiated the reduced ion transport responses seen in dextran sulfate sodium (DSS)-treated and mdr1a knockout mouse colon. Ion substitution studies and the sodium transport inhibitor amiloride showed that sodium movement primarily accounted for the potentiating effect of EGF in DSS-treated tissues, despite decreased sodium channel expression. EGF potentiation of transport responses in DSS-treated colon was completely blocked by the cytoskeletal disruptor cytochalasin D and the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas the novel and conventional protein kinase C isoform inhibitor G?6850 and the extracellular signal-regulated kinase inhibitor PD98059 partially reduced EGF effects. EGFR epithelial distribution and transforming growth factor alpha expression were also altered in DSS-treated tissues. CONCLUSIONS: Chronic inflammation uncovers a potentiating effect of EGFR activation on epithelial electrogenic sodium absorption that would be expected to ameliorate diarrheal symptoms associated with colitis.