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At least 793 records · Page 44Linked to original sources
PubMed1985

Contractile effect of short-chain fatty acids on the isolated colon of the rat.

The contractile effect of short-chain fatty acids on proximal, middle and distal segments of the rat colon was studied in vitro. A single contraction of the longitudinal muscle of the everted preparation of the middle and distal but not the proximal colon was induced by mucosal application of propionate, butyrate or valerate. Sigmoid dose-responses were observed between contraction and log dose of propionate, butyrate and valerate. The threshold concentration of short-chain fatty acids was between 0.02 and 0.04 mM. A maximal contraction was induced with 0.1 mM-propionate, butyrate and valerate. While acetate (up to 10 mM) and lactate (up to 30 mM) had no contractile effect at all. Serosal application of short-chain fatty acids was without effect, while the contractile response with up to 10 mM-propionate was abolished in both the middle and distal colon by scraping away the mucosa. Cumulative addition of short-chain fatty acids to the organ bath (without wash-out of the first dose) caused adaptation of the contractile response; thus, the effect of propionate (1 mM) was abolished by prior addition of acetate (10 mM) or lactate (30 mM) or propionate (1 mM) or butyrate (1 mM) or valerate (1 mM). The contractile effect of propionate was also inhibited by atropine (1 microM), procaine (0.4 mM) and tetrodotoxin (3 microM); was unaffected by hexamethonium (0.1 mM) and enhanced by eserine (10 nM). The results suggest that short-chain fatty acids, which are normal constituents of the colon, have the ability to stimulate colonic contractions, probably via an enteric reflex involving local sensory and cholinergic nerves.

Adaptation, Physiological↗
PubMedDate not supplied

Effects of hyperthermia and membrane-active compounds or low pH on the membrane fluidity of Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells heated in the presence of the membrane-active agents procaine, ethanol, butylated hydroxytoluene (BHT) and glycerol were analysed for changes in fluorescence polarization of the lipid probe (1-[4(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene, an indicator of plasma membrane fluidity). Cells were heated in normal and acid (pH 6.6) medium. Procaine, ethanol, BHT and low pH sensitized cells to heat-killing. Procaine, ethanol and BHT decreased fluorescence polarization (increased plasma membrane fluidity) significantly. Polarization distributions for cells heated with these sensitizers were broadened substantially and were skewed toward lower polarization values. Glycerol, a heat-protector, inhibited changes in fluorescence polarization due to heating at temperatures up to 45.0 degrees C. Heating cells at either 42 or 45 degrees C in pH 6.6 medium had no significant effect on the fluorescence polarization compared with controls, while survival was reduced substantially. Thus, heat-sensitization of low pH cannot be ascribed to changes in membrane fluidity. The changes in membrane fluidity caused by other sensitizers and protector indicate that membrane fluidity changes may be a contributing cause of cell killing by hyperthermia.

Animals↗
PubMed1996

Stimulation of cortical actin polymerization in the sea urchin egg cortex by NH4Cl, procaine and urethane: elevation of cytoplasmic pH is not the common mechanism of action.

Previous studies have demonstrated that the penetrating weak base NH4Cl and the anesthetics procaine and urethane disrupt the normal attachment of cortical granules to the cortex of the sea urchin egg. Hylander and Summers (1981: Dev. Biol. 86:1-11) hypothesized that this effect may be caused by a pH-induced polymerization of cortical actin. We have tested this hypothesis by measuring the intracellular pH of eggs of the sea urchins S. purpuratus and A. punctulata treated with NH4Cl, procaine, or urethane, and determining the effects of these agents on the organization of cortical actin. Intracellular pH was determined by the ratiometric measurement of the fluorescent dye BCECF, and filamentous actin organization was examined by confocal laser scanning microscopy of BODIPY-phallocidin stained eggs. Treatment of eggs with either NH4Cl or procaine resulted in a rapid and reversible increase in cytoplasmic pH of up to 1 pH unit and a dose-dependent increase in the intensity of fluorescent staining of the cortex, indicating an increase in the content of filamentous actin. While urethane also induced a dramatic polymerization of cortical actin, no effect on cytoplasmic pH could be detected. These results demonstrate that NH4Cl, procaine and urethane all induce an increase in the amount of filamentous actin in the sea urchin egg cortex that may participate in the detachment of cortical granules. However, these compounds do not share a common mechanism of action based on the elevation of cytoplasmic pH.

Actins↗
PubMed1978

The mode of action of antagonists of the excitatory response to acetylcholine in Aplysia neurones.

1. The mode of action of various antagonists of acetylcholine (ACh) excitatory effects on Aplysia neurones was studied under voltage clamp. ACh was applied by iontophoresis whereas antagonists were applied in the bath. Tubocurarine and hexamethonium were the most thoroughly studied compounds. 2. The 'elementary current', calculated as the ratio of the variance of the ACh noise to the mean ACh induced current, was not modified by any of the antagonists tested. 3. The evolution of the ACh induced current after a voltage jump, which is normally described by a single exponential, was modified by all the antagonists tested. A common feature of the modified relaxations was the appearance, over a certain concentration range of the antagonist, of two successive and opposite exponential components. 4. The characteristics of the composite relaxations depend on the antagonist. For a given antagonist they vary with membrane potential, ACh concentration, and antagonist concentration. 5. The noise power spectra of the ACh induced current showed changes consistent with those of the relaxations. 6. In the absence of antagonists, the current induced by a steady application of ACh increases linearly with hyperpolarization. In the presence of antagonists, the I-V curve shows a marked curvature, indicating a proportionally larger reduction of the ACh response at more negative membrane potentials. 7. The voltage sensitivity of the blocking action of hexamethonium and decamethonium is noticeably stronger than that of monovalent antagonists. 8. A model is proposed which accounts for the observed effects. It assumes that the antagonists studied bind perferentially to the 'activated' ACh-receptor complex, and convert it to a non-conducting state. Kinetic constants can be calculated for this reaction; e.g. for curare, at 12 degrees C and -80 mV, the dissociation and association constants were estimated at 0.1 sec-1 and 4 X 10(5) M-1 sec-1. 9. Partial replacement of the extracellular Na by Tris modifies the relaxations observed in the presence of hexamethonium. Hexamethonium appears less effective in the presence of Tris, which supports the hypothesis that the binding site of the antagonists is linked to the ionic channel.

Acetylcholine↗
PubMed1984

Effects of noradrenaline and acetylcholine on electro-mechanical properties of the guinea-pig portal vein.

Effects of acetylcholine (ACh) and noradrenaline (NA) on mechanical properties of smooth muscle cells of the guinea-pig portal vein were investigated using intact and skinned muscle preparations. In some preparations, the electrical activity was also recorded. In addition to ACh and NA, the effects of caffeine, procaine, excess concentrations of [K]o and MnCl2 were investigated. NA enhanced the mechanical response due to increase in the spike generation, receptor activated depolarization and release of Ca stored in the cell. ACh also enhanced the mechanical response, but this agent had little effect on the Ca release from the storage sites. Caffeine and procaine (10 mM) depolarized the membrane and enhanced the electrical activity. Caffeine enhanced the mechanical activity due to an increase in the membrane activity and the release of Ca stored in the cell, while procaine inhibited the contraction. Procaine inhibited and caffeine accelerated the Ca-induced Ca-release mechanism in the cell. NA released the Ca from the storage sites to a greater extent than did caffeine or ACh. MnCl2 inhibited the spontaneous membrane activity and contraction; however, low concentrations of MnCl2 increased the caffeine- or NA-induced contraction in Ca-free solution. When the Ca-tension relationship was observed in saponin-treated skinned muscles, the minimum concentration of Ca required to produce the contraction was 10(-7)M, as observed in other vascular tissues. Caffeine released the stored Ca, Na and ACh had no effect on the Ca release and procaine inhibited the caffeine-induced Ca release in skinned muscles. It was concluded that the membrane properties of smooth muscle cells in the portal vein are much the same as observed in other spontaneously active visceral muscles. Differences observed in the actions of NA and ACh on mechanical properties seems to be mainly due to different receptor-operated Ca release mechanisms.

Acetylcholine↗
PubMed1979

The local anesthetic effect of cyproheptadine on mammalian nerve fibres.

The local anesthetic effect of cyproheptadine on nerve fibres in the rabbit's cervical vagus and sciatic nerve was studied by the single sucrose-gap technique. Local anesthetics such as procaine and tetracaine, and an antihistaminic with local anesthetic activity, diphenhydramine, were studied for comparison. Increasing concentrations of cypropheptadine, starting from 5 x 10(-5) M, produced a dose-related fall in the amplitude of the compound action potential of the vagus nerve without significant change in the resting membrane potential. A complete reversibility of the local anesthetic effect was difficult or impossible to obtain when doses greater than 1 x 10(-4) M were used. Cyproheptadine was more potent than procaine and diphenhydramine, and less potent than tetracaine in producing nerve conduction block. Frequency-dependent block was observed with cyproheptadine and the other agents at frequencies that can be considered low (1--5 Hz). Myelinated fibres of the sciatic nerves were also blocked by cyproheptadine within the same range of concentrations (1 x 10(-4) to 1 x 10(-3) M). Our results provide an additional explanation for the mechanism underlying the actions of cyproheptadine as an antiarrhythmic and an antipruritic agent.

Action Potentials↗
PubMed1976

Effects of local anaesthetics on intracellular fusion processes. Enhancement of concanavalin A-induced macrophage vacuolation.

The extensive vacuolation elecited in mouse peritoneal macrophages in response to interaction with concanavalin A is markedly enhanced by a simultaneous exposure to anaesthetics. The potency of enchancing vacuolation increases within the series of normal alcohols with chain length C10 greater than C8 greater than C7 greater than C6. From the four tertiary amine local anaesthetics tested lidocaine and procaine are by far more effective than tetracaine and dibucaine. The latter two induce extensive cell shrinkage at concentrations at which the first two exhibit optimum enhancing capacity. Of the tested compounds chlorpromazine has the highest membrane/buffer partition coefficient and it exhibits its optimum enhancing effect on concanavalin A-induced macrophage vacuolation at the lowest drug concentration. The binding of [3H] concanavalin A as well as its internalization by macrophages incubated with the lectin for 15, 45 and 90 min are not affected significantly in the presence of decanol, procaine or chlorpromazine at concentrations of maximum enhancing effect on vacuolation. Thus enhancement of vacuolation does not stem from an increase in the rate or extent of concanavalin A interiorization. The rate at which vacuoles are generated is however markedly increased in the presence of chlorpromazine and the resulting vacuoles are of a larger diameter. At 2-5 fold the concentration required for inhibition of maximum enhancing effect, the drugs lead to extensive macrophage shrinkage and to depletion of intracellular ATP. Phagocytosis of heat-killed yeast cells is reduced by tertiary amine anaesthetics at concentrations optimal for enhancement of concanavalin A-induced vacuolation. Enhanced intracellular fusion of concanavalin A-bearing pinosomes to form vacuoles is discussed in terms of current ideas on factors vacuoles is discussed in terms of current ideas on factors vacuoles is discussed in terms of current ideas on factors affecting membrane fusion and the effects of anaesthetics on membrane organization of lipids, intramembraneous particles, glycoprotein receptors and the possible control by cytoskeletal elements. The results best fit the hypothesis that enhanced fusion correlates with membrane aggregation of both intramembraneous particles and concanavalin A receptor and the formation of areas relatively deplete of these structures and enriched in phospholipids.

Adenosine Triphosphate↗
PubMed1995

BaCl2- and 4-aminopyridine-evoked phasic contractions in the rat vas deferens.

1. The actions of BaCl2 and 4-aminopyridine, blockers of K+ channels, on the mechanical activity of the epididymal half of the rat vas deferens were investigated. 2. Both BaCl2 and 4-aminopyridine dose-dependently evoked phasic contractions. High extracellular potassium (35-40 mM) caused a tonic contraction but abolished the BaCl2- and 4-aminopyridine-induced phasic activity and reduced the BaCl2-induced sustained component of contraction, but increased the 4-aminopyridine-induced tonic contraction. 3. Omission of calcium from the extracellular medium totally abolished the 4-aminopyridine-induced response but only reduced the mean amplitude of phasic contractions induced by BaCl. 4. Procaine (10 mM), an inhibitor of internal calcium release, completely abolished the phasic activity and reduced the sustained contraction induced by BaCl2. The remaining tone was abolished by nifedipine (1 microM). 5. Tetraethylammonium (1 mM) suppressed the amplitude of the BaCl2-induced phasic contractions, and induced a biphasic increase in tonic tension. 6. The BaCl2-induced responses were resistant to prazosin (1 microM), yohimbine (3 microM), propranolol (3 microM) or atropine (3 microM); in contrast, the 4-aminopyridine-induced activity was effectively inhibited by prazosin (1 microM) attenuated by yohimbine (1 microM) and atropine (1 microM) but not by propranolol (3 microM). The 4-aminopyridine-induced response was abolished by pretreatment of the vas deferens with 6-hydroxydopamine (0.5 mM). 7. The results indicate that the BaCl2-evoked activity in the vas deferens was mainly due to blockade of Ba(2+)-sensitive K+ channels on the smooth muscle plasma membrane. Subsequent calcium entry through the depolarized plasma membrane was needed to trigger generation of phasic contractions. 4-Aminopyridine-induced action, however, was largely mediated by neurotransmitters released from the depolarized nerve terminals as a result of blockade of K+ channels.

4-Aminopyridine↗