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PubMed1976

Quantitative morphological study of smooth muscle cells of the guinea-pig taenia coli.

A quantitative study of muscle cells of the guinea-pig taenia coli is reported. Stereological methods were used on electron micrographs and phase contrast micrographs. Smooth muscle cells of taeniae fixed under 1 gram load were about 515 mum long. Muscle cell volume was about 3,500 mum3 and cell surface 5,300 mum2. About 168,000 caveolae were found at the surface of each muscle cell, covering about 29% of its surface. They produced a 73% increase of the cell membrane compared to a smooth-surfaced cell. The ratio surface-to-volume is about 1:0.67 if the geometrical surface is considered, or 1:0.39 if the total surface of the cell membrane (including the caveolae) is considered. Mitochondria constituted 3.5-4% of the cell volume. A few nexuses were observed, both between two muscle cells and between a muscle cell and an interstitial cell. In serial sections septa of connective tissue and groups of muscle cells were found to disappear within few tens of microns or to merge with other septa, and the taenia did not appear to be divided into clear-cut muscle cell bundles. Bundles of smooth muscle cells were seen passing from the taenia to the underlying circular muscle. The transverse sectional area of the taenia ranged between 0.14 and 0.39 mm2; it showed about 526 blood vessels-mm-2.

Animals↗
PubMed1994

Activation of diacylglycerol kinase by carbachol in guinea pig taenia coli.

Changes in diacylglycerol kinase (DG kinase) activity in carbachol (CCh)-stimulated guinea pig taenia coli were investigated. In a mixed micellar assay system, added 1,2-dioctanoyl-sn-glycerol (diC8) and endogenous DG were competitively bound to common DG kinase isozymes from guinea pig taenia coli and phosphorylated, suggesting that diC8 is useful as a probe of agonist effects on DG kinase activity. In phosphorus-32 ([32P]Pi)- and diC8-prelabeled guinea pig taenia coli, diC8 was phosphorylated by DG kinase to [32P]dioctanoyl-phosphatidic acid ([32P]diC8-PA). CCh increased the accumulation of both [32P]diC8-PA and endogenous [32P]phosphatidic acid ([32P]PA) in a time- and dose-dependent manner (0.1-100 microM CCh). CCh-induced increases in [32P]diC8-PA and [32P]PA were inhibited by 1 microM atropine and 3 microM DG kinase inhibitor (R59022). These findings indicated the activation of DG kinase by muscarinic receptor stimulation in guinea pig taenia coli. Therefore, DG kinase activation may play an important role in CCh-induced PA formation. CCh-induced [32P]diC8-PA and [32P]PA accumulation was dependent on intracellular calcium concentrations. However, a KCl-induced increase in intracellular calcium, without receptor stimulation, was ineffective. Moreover, treatment with phorbol ester also increased accumulation of both PA species in KCl-treated tissues. These findings suggest that muscarinic receptor mediated activation of DG kinase may require both an increase in intracellular calcium and PKC activation in guinea pig taenia coli.

Animals↗
PubMed1984

The contribution of calcium and potassium to the alpha-action of adrenaline on smooth muscle cells of the portal vein, pulmonary artery and taenia caeci of the guinea-pig.

The role of calcium and potassium in the alpha-action of adrenaline in pulmonary artery and portal vein was compared with that in taenia caeci by measuring changes in membrane potential, muscle contraction and ion fluxes in quiescent preparations from guinea-pigs (23 degrees C). The depolarization evoked by adrenaline (5 x 10(-8)-3 x 10(-5) M) was sustained in portal vein; in pulmonary artery it declined to a constant level after reaching an initial maximum. In calcium-free medium (20 min) containing EGTA (0.4 mM) and high magnesium (6.2 mM) adrenaline did not affect the membrane potential or the contractile state of the portal vein. Under these conditions the sustained phase of the response was abolished in the pulmonary artery; the remaining transient depolarization and contraction could be evoked only once. Adrenaline (3 x 10(-5) M) caused an increased 45Ca loss and 86Rb loss from the pulmonary artery and taenia caeci in calcium-free solution; a second addition of adrenaline to the calcium-free solution did not enhance the 45Ca loss from these tissues. The portal vein responded with an enhanced 86Rb loss on addition of the alpha-agonist. The bee toxin apamin (3 x 10(7) M) did not modify the depolarization, the contraction or the 45Ca and 86Rb fluxes evoked by adrenaline in the blood vessels. Enhancement of the 86Rb loss from taenia in the presence of adrenaline was prevented by apamin, but the excess loss of 45Ca was not abolished. It is concluded that adrenaline enhances cytoplasmic calcium by promoting calcium entry from the extracellular space in portal vein. In pulmonary artery and taenia caeci this is accompanied by mobilization of calcium from a cellular structure. Calcium entry facilitates triggering of the contractile proteins in vascular smooth muscle and is associated with membrane depolarization; in taenia caeci the mobilization of calcium caused by alpha-receptor activation is associated with the opening of potassium channels producing hyperpolarization and accordingly relaxation of the smooth muscle cells.

Animals↗
PubMed1986

Effects of cadmium ions, D-600 and chlorpromazine on the skinned smooth muscle of guinea-pig taenia coli.

The effects of Cd2+ on the skinned taenia coli were compared with that of Ca2+ channel blocker, D-600 and calmodulin inhibitor, chlorpromazine. The Cd2+ (0.001-0.5 mM) inhibited the contraction of skinned fibres in a dose-dependent manner. In contrast, the contraction of skinned fibres was not inhibited by pretreatment with 1 X 10(-6) M D-600. However, chlorpromazine (10(-4) M) inhibited the contraction of skinned taenia coli. The inhibition of contraction by Cd2+ in skinned taenia coli was completely reversed by washing with solution containing EDTA, following a treatment with 0.5 mM Cd2+ for 15 min. The skinned fibres had rapidly taken up a far greater amount of Cd2+ than intact muscle of taenia coli. EDTA increased Cd2+ efflux in skinned fibres and only 5% of the original tissue content retained. Thus, EDTA, which was ineffective on intact taenia coli, can be considered to act on Cd2+ of intracellular compartment after disruption of the cell membrane with saponin. In conclusion, there is the possibility that Cd2+ inhibits the contractile system, such as contractile proteins and calmodulin, which results in tension inhibitory effect.

Animals↗
PubMed1990

The pig as an intermediate host for Taiwan Taenia infection.

Eggs (1000-100,000/animal) of Taiwan Taenia were inoculated per os into 14 Small-Ear-Miniature (SEM), 19 Landrace-Small-Ear-Miniature (L-SEM), and 5 Duroc-Yorkshire-Landrace (DYL) pigs. These animals were sacrificed 7-107 days after infection. Thirty-four pigs were found to be infected with Taiwan Taenia cysticerci and the infection rates of SEM, L-SEM, and DYL were 86%, 89% and 100% respectively. The cysticerci recovery rates of SEM, L-SEM and DYL pigs were 27.2%, 1.7% and 0.27% respectively. Cysticerci were recovered only from the livers and none were found in muscles, viscera or other parts of the carcasses. More cysticerci were located in the liver parenchyma (71%) than on the liver surface (29%). Taiwan Taenia cysticerci were smaller than those of classical T. saginata or T. solium. Moreover, Taiwan Taenia cysticerci had 2 rows of rudimentary hooklets on the scolex. The results of this study indicate that young pigs are good intermediate hosts for Taiwan Taenia and that the SEM pig is a satisfactory host for experimental studies with this tapeworm. These results were similar to other studies with different geographic strains of the T. saginata-like tapeworm in the Far East. These strains appear to be the same and possibly a new species.

Animals↗
PubMed1997

Epidemiological study of Taenia solium infections in a rural village in Honduras.

An epidemiological study was conducted in a Honduran rural community in 1991, to determine the local prevalence and associated risk factors of Taenia infection. The seroprevalence of anti-cysticercus antibodies, investigated by ELISA (N = 526), was found to be 30%. The prevalence of intestinal infections with Taenia and other parasites was investigated, by formol-ether concentration of three stool samples from each subject (N = 536). Almost all (96%) of the subjects carried at least one of the 17 species of intestinal parasite identified, 11 (2%) of them (nine of them female) being found to be infected with Taenia spp. When nine of these 11 were given niclosamide, four expelled Taenia segments, all of which were identified as T. solium after carmine staining. Risk factors associated with seropositivity were earthen floor, overcrowding, previous taeniasis and living in the same household as a person reporting previous taeniasis. Four years later (1995), a follow-up study in a sub-sample of the previously studied population revealed that 34% of the subjects were seropositive for anti-Taenia solium antibodies (as determined by a cysticercosis-specific, enzyme-linked, immunoelectrotransfer, blot assay) and that 1.5% had taeniasis. Taeniasis and cysticercosis therefore appear to be important public-health problems in rural areas of Honduras, as they are in other countries of Latin America. Large-scale studies need to be conducted to facilitate the design of programmes to control these diseases.

Adolescent↗
PubMed1972

The effect of cold storage on the inhibitory action of isoprenaline, phenylephrine and nicotine on the mechanical and membranal activities of guinea-pig taenia caecum.

1. The effects of prolonged cold storage on the mechanical and membranal responses to stimulation of alpha- and beta-adrenoceptors by phenylephrine and isoprenaline, respectively, were studied on the guinea-pig taenia caecum.2. Cold storage invariably caused a decrease in the resting membrane potential, and this effect was enhanced as the duration of treatment was prolonged.3. After cold storage (18 days) the tissue potassium ion content (89.7 +/- 1.7 mmol/kg wet wt.) was decreased to 30.5 +/- 1.9 mmol/kg wet wt. whereas that for sodium (69.2 +/- 1.4 mmol/kg wet wt.) increased to 134.0 +/- 2.3 mmol/kg wet wt.4. In the fresh preparations, phenylephrine (1 and 2 muM) caused a cessation of spontaneous action potentials, accompanied by hyperpolarization of the membrane and relaxation of the muscle. These effects were markedly diminished after 18 days of cold storage. Isoprenaline (1 and 2 muM) also blocked the action potentials and caused a concomitant muscle relaxation, but in most cases the hyperpolarization was not observed. After 14 days of cold storage these mechanical and membranal changes associated with isoprenaline treatment were not demonstrable in most preparations.5. Nicotine (5 muM and 50 muM) produced a biphasic effect, cessation of the action potential, hyperpolarization and subsequent relaxation followed by a long lasting depolarization, an accelerated discharge of action potentials and an increase in muscle tension. After a few days of cold storage the hyperpolarization effect disappeared but the intensity of the long-lasting depolarization as well as the contractile effects were increased. After cold storage for more than 7 days, nicotine did not affect mechanical or electrical activity.6. Dibutyryl 3'5' cyclic AMP (1 muM to 500 muM) failed to affect the mechanical and electrical activities of taenia caecum.7. Phenylephrine and isoprenaline had no effect on the high potassiumdepolarized taenia.8. These observations suggest that the electro-mechanical effect of an alpha-adrenoceptor stimulant on the guinea-pig taenia caecum is more resistant to cold treatment than that of a beta-adrenoceptor stimulant. This inhibitory system of stimulation of both a- and 8-receptors of guinea-pig taenia caecum may react by different mechanisms. The results also demonstrate that cold storage itself changes the membrane permeability to ions and the tissue ion content (Na+ and K+) of smooth muscle of guinea-pig taenia caecum.

Action Potentials↗
PubMed1980

Effects of hydralazine and verapamil on phosphorylase activity and guanosine cyclic 3',5'-monophosphate levels in guinea-pig taenia coli.

1 The roles of guanosine cyclic 3',5'-monophosphate (cyclic GMP) and calcium in the relaxation produced by hydralazine and verapamil in potassium-depolarized guinea-pig taenia coli have been investigated.2 Depolarization of isolated strips of guinea-pig taenia coli by 124 mM KCl caused sustained contractures and increases in tissue levels of cyclic GMP.3 The KCl-induced increases in cyclic GMP levels appeared to be calcium dependent. No increases in cyclic GMP levels were seen in strips of taenia coli depolarized in the absence of calcium. Readdition of calcium to the depolarizing solution contracted the muscles and increased cyclic GMP levels. When calcium was removed from the depolarizing solution during the sustained, tonic phase of a KCl-induced contracture, both tension and cyclic GMP levels returned to control values.4 Administration of 50 muM verapamil to KCl-contracted muscles completely relaxed the muscles and caused cyclic GMP levels to return to control values within 14 min. Hydralazine, 2 mM, on the other hand, relaxed the depolarized muscles without lowering cyclic GMP levels. No significant changes in cyclic AMP levels were seen in any of these experiments.5 Similar results were obtained in an analogous series of experiments in which glycogen phosphorylase activity was measured instead of cyclic GMP levels. Activation of phosphorylase during contractions of guinea-pig taenia coli had previously been reported to be a calcium-dependent phenomenon.6 It was concluded that increases in tissue levels of cyclic GMP (or of cyclic AMP) were not responsible for the relaxant effects of hydralazine or verapamil in these experiments. It was also suggested, based on our results, that verapamil exerted its relaxant effects in the depolarized taenia coli by lowering cytoplasmic calcium levels, whereas hydralazine relaxed the depolarized muscles without lowering intracellular calcium activity.

Animals↗
PubMed1984

Comparative effects of verapamil and sodium nitroprusside on contraction and 45Ca uptake in the smooth muscle of rabbit aorta, rat aorta and guinea-pig taenia coli.

The effects of verapamil and sodium nitroprusside on muscle tension and 45Ca uptake activated in different ways were compared in rabbit aorta, rat aorta and guinea-pig taenia coli. In rabbit aorta, K-induced contraction was specifically inhibited by verapamil and noradrenaline-induced contraction by sodium nitroprusside. In rat aorta, both K-induced and noradrenaline-induced contractions were inhibited by verapamil or by sodium nitroprusside also. In taenia, both K- and histamine-induced sustained contractions were inhibited by verapamil but not by sodium nitroprusside. The effect of verapamil was competitively antagonized by external Ca, while that of sodium nitroprusside was not. High K, noradrenaline and histamine increased the rate of 45Ca uptake in aortae and taenia. In rabbit aorta the increment in response to high K was specifically inhibited by verapamil and the increment induced by noradrenaline was specifically inhibited by sodium nitroprusside. In rat aorta, increments induced by both high K and noradrenaline were inhibited by verapamil and by sodium nitroprusside. In taenia, the increments induced by high K and by histamine were inhibited by verapamil but not by sodium nitroprusside. These results suggest different characteristics of Ca entry systems in these smooth muscles. In rabbit aorta, there seem to be two Ca channels, one of which is activated by high K and inhibited by verapamil, while the other is activated by noradrenaline and inhibited by sodium nitroprusside. In rat aorta, both K- and noradrenaline-activated Ca pathways are sensitive to both verapamil and sodium nitroprusside whereas, in taenia, both K- and histamine-activated Ca pathways are sensitive only to verapamil.

Animals↗
PubMed1984

The binding of cadmium ions to the smooth muscle of guinea-pig taenia coli.

Taenia coli was used to study the property of binding of Cd2+. The Scatchard plots of cadmium uptake showed that two qualitative Cd2+ binding sites (high and low affinity binding sites) exist in taenia coli. Decrease in Ca2+ concentration in the medium did increase the cadmium binding. The Scatchard analysis of Cd2+ binding in taenia coli at 4 degrees indicated a single class of binding sites (only high affinity binding sites). These findings suggest that the greater number of high affinity Cd2+ binding sites in taenia coli may relate to the binding to cell membrane. Further, it was postulated that some of low affinity binding sites in taenia coli may reflect intracellular accumulation, indicating the action on the contractile system.

Animals↗
PubMed1985

The effects of K+-depolarization medium, chelating agents and thiol groups on cadmium uptake and efflux in the guinea-pig taenia coli.

Cadmium uptake by taenia coli was dose-dependent, achieving equilibrium after approximately 60 min of incubation. The SH-blocker, N-ethylmaleimide inhibited cadmium uptake. When muscles were washed with normal medium or that containing 0.5 mM EDTA following 0.5 mM Cd2+ treatment for 60 min, the tissue cadmium concentration reached equilibrium levels after 60 min and approximately 43 or 27% of the initial tissue cadmium concentration was retained, respectively. Both glutathione and dithiothreitol also increased cadmium efflux. However the contractions of glycerinated taenia coli caused by Ca2+ and Mg-ATP, completely returned to control values after washing with 0.5 mM EDTA medium following 0.5 mM Cd2+ treatment for 60 min, suggesting that EDTA seems to exert intracellular effects in glycerinated taenia coli. These results suggest that SH-dependent mechanisms in cadmium uptake play a role in intact taenia coli. In addition, in intact taenia coli, Cd2+ are accumulated in intracellular compartments which EDTA cannot reach and may exert an inhibitory action on internal sites in the cells.

Animals↗
PubMed1971

Changes in the physiology and fine structure of the taenia of the guinea-pig caecum following transplantation into the anterior eye chamber.

1. The taenia of the guinea-pig caecum has been used as a model to study the re-establishment of autonomic innervation following transplantation into the anterior eye chamber. The ultrastructure, the histochemical localization of noradrenaline and acetylcholinesterase and the pharmacology of transmission to the taenia have been examined 1 day to 16 weeks following transplantation. Both ganglion-free strips of the taenia and caecal wall segments including the underlying Auerbach's plexus were used.2. Caecal wall preparations: nerve fibres from intramural ganglion cells retracted during the first 2 days following transplantation, but reappeared in the muscle soon afterwards. Adrenergic nerves from the iris formed terminals about ganglion cells at about 2-4 weeks. Both cholinergic excitatory and non-adrenergic (;purinergic') inhibitory transmission to the muscle was re-established by 2-4 days following transplantation.3. Taenia strip preparations: both adrenergic and cholinergic nerve fibres were demonstrated histochemically in muscle bundles by 2-4 weeks. Non-adrenergic inhibitory and cholinergic transmission was not re-established until 2-4 weeks following transplantation. There was an abnormally dense re-innervation of the muscle by adrenergic nerve fibres by about 8 weeks which is compared with the innervation of aganglionic bowel in Hirschsprung's disease.4. The origin of non-adrenergic inhibitory responses in the transplanted taenia is discussed and the results considered in relation to the re-innervation of transplants of the vas deferens and of intestine during early development.

Acetylcholinesterase↗
PubMed1990

The effect of loop diuretics on Cl- transport in smooth muscle of the guinea-pig vas deferens and taenia from the caecum.

1. The role of Na+, K+, Cl- co-transport, identified in the previous paper (Aickin & Brading, 1990), has been characterized further by investigation of the effects of loop diuretics on Cl- movements in the smooth muscle cells of guinea-pig vas deferens measured by 36Cl fluxes and Cl(-)-sensitive microelectrodes. Some flux experiments were also repeated in the taenia from the guinea-pig caecum. 2. Frusemide (2 mM) reduced the steady-state Cl- content, slowed 36Cl loss into Cl(-)-free solution and both slowed and reduced Cl- accumulation by Cl(-)-depleted cells of the vas deferens. When anion exchange was inhibited by the presence of DIDS, (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid), frusemide further slowed the loss of Cl- into Cl(-)-free solution, further reduced Cl- accumulation such that Cl- uptake amounted to a level consistent with a passive distribution and halted the rise in the intracellular Cl- activity (aiCl) at levels above about 10 mM. 3. Application of the higher-affinity loop diuretics bumetanide and piretanide in vas deferns had no significant effect on 36Cl efflux into Cl(-)-free solution or on the initial rate of rise of aiCl but reduced the final level attained. In the presence of DIDS, however, both agents further slowed efflux into Cl(-)-free solution, and halted the rise in aiCl at levels above about 10 mM. Measurement of greatly slowed intracellular pH transients on removal and readdition of external Cl- (Clo-) in the presence of frusemide suggests that the larger effects of this drug are mediated by inhibition of anion exchange as well as of co-transport. 4. The relative potency of the loop diuretics, investigated in the presence of DIDS was: bumetanide greater than piretanide greater than frusemide. This sequence was found in both vas deferens, using direct measurement of aiCl, and taenia, using 36Cl uptake. 5. Comparison of data from the vas and taenia showed that 36Cl efflux into Cl(-)-free, HCO3(-)-free solution was about twice as fast in the taenia, and that bumetanide or piretanide reduced this efflux to about the same rate as that observed in the vas with or without the loop diuretic. DIDS caused a similar absolute reduction of efflux in both preparations. 6. Stimulation of 36Cl efflux on readdition, and inhibition on removal of Nao+ in the presence of DIDS, was much greater in the taenia than in vas and in both preparations was blocked by bumetanide or piretanide.(ABSTRACT TRUNCATED AT 400 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Effects of hypoxia on high-energy phosphagen content, energy metabolism and isometric force in guinea-pig taenia caeci.

1. Previously, Ishida, Takagi & Urakawa (1984) reported that, in the presence of high K+ (45.4 mM) under hypoxia (95% N2-5% CO2 bubbling), tension and ATP content of the smooth muscle of the guinea-pig taenia caeci increased concomitantly when the glucose concentration was raised. Tension and energy metabolism of the taenia seemed to be closely correlated. In the present experiments, we investigated the metabolic changes during the relaxation phase after the taenia was exposed to hypoxia in the presence of high K+ by measuring the content of phosphagen, inorganic phosphate (Pi) and lactate in the tissue. Oxygen consumption and lactate release from the tissue were also determined to estimate the rate of ATP synthesis. 2. Under hypoxic conditions, high-K(+)-induced tension decreased to one-tenth of maximum in aerobic conditions (95% O2-5% CO2 bubbling); increasing the calcium concentration from 2.5 to 10 mM had no effect. To test receptor-associated stimuli, carbachol or histamine (both 5 microM) had little effect on tension in hypoxia. The calcium ionophore A23187 (10 microM) also did not produce any significant contraction in the presence of high K+ under hypoxia. 3. Hypoxia in the presence of high K+ elicited a rapid decrease in phosphocreatine, approximately in parallel with the decrease in tension. The ATP content decreased gradually while Pi content increased. Lactate content increased rapidly and then partially decreased. 4. The rate of ATP synthesis estimated from the oxygen consumption and lactate release of the taenia was linearly correlated with tension development under aerobic and hypoxic conditions. 5. These results suggest that the decrease in tension of the taenia observed under hypoxic conditions is due to an inhibition of energy metabolism, and not due to an oxygen-sensing step in excitation-contraction coupling.

Adenine Nucleotides↗
PubMed1983

Pharmacological characterization of ionophore X537A-induced contractile responses in isolated rabbit taenia coli and aorta.

Pharmacological action of ionophore X537A was studied in taenia coli and aortic strips isolated from rabbit. These isolated smooth muscle preparations contracted by X537A (10(-5)-10(-4) M). A removal of Ca ions from the buffer solution considerably reduced the contraction of taenia coli but not that of aorta. D 600 (methoxyverapamil, 10(-6) M) was without any effect in the contraction of both tissues by X537A (10(-4) M). However, papaverine (10(-4) M) and Aspaminol (1, 1-diphenyl-3-piperidinobutanol hydrochloride, 10(-4) M) inhibited X537A (10(-4) M)-induced contraction markedly in taenia coli but slightly in aorta. Inhibitory effects of these drugs were reversed in taenia coli by increasing Ca ion concentration in buffer solution but not in aorta. X537A (10(-4) M)-induced contraction of aorta was not affected by a pretreatment of rabbit with reserpine and preincubation of the isolated preparations with guanethidine (10(-6) M) or prazosin (10(-7) M). These results suggest that ionophore X537A might produce the contraction through an increase of Ca influx in isolated rabbit taenia coli which are little or not affected by D 600, whereas the contraction of rabbit aorta induced by X537A is mainly due to facilitation of release of Ca sequestered intracellularly.

Animals↗
PubMed1983

The actions of D 600, aspaminol and papaverine on calcium-, potassium- and histamine-induced contractions of isolated rabbit basilar artery, aorta, taenia coli and tracheal smooth muscle.

The effects of D 600, Aspaminol (1,1-diphenyl-3-piperidinobutanol hydrochloride) and papaverine on CaCl2-, KCl- and histamine-induced contractile responses of isolated rabbit basilar artery, aorta, taenia coli and tracheal smooth muscle were compared with each other. D 600 reduced CaCl2-induced maximal responses in basilar artery and aorta, and parallelly shifted the concentration-response curves for CaCl2 to the right in taenia coli and trachea. D 600 also reduced histamine-induced maximal contractions in basilar artery and taenia coli. These reductions were not reversed by increasing CaCl2 concentration in bathing fluids. High concentration of D 600 parallelly shifted the concentration-response curve for histamine to the right in aorta. Like D 600, Aspaminol, a nonspecific smooth muscle relaxant, parallelly shifted the concentration-response curve for histamine in aorta. Papaverine parallelly shifted the concentration-response curve for CaCl2 in taenia coli and reduced the maximal responses in other tissues. Papaverine also reduced histamine-induced maximal responses in basilar artery, aorta and taenia coli. Influences of these smooth muscle relaxants on histamine-induced contraction in Ca-free buffer solution and on KCl-induced contraction in normal and high Ca (Ca: 12.5 mM) buffer solution were also studied. From the results obtained in this study, the effects of smooth muscle relaxants are considered to vary with the type of smooth muscle or the condition eliciting contraction, and the possible mechanisms of the contractions were discussed.

Animals↗
PubMed1985

Possible mechanisms of inhibitory action of sodium nitroprusside on histamine-induced contractile responses in isolated rabbit aorta compared with basilar artery and taenia coli.

Possible mechanisms of the inhibitory actions of sodium nitroprusside (NaNP) on histamine-induced contractile responses of isolated rabbit aorta, basilar artery and taenia coli were studied. NaNP (3 X 10(-5) M) reduced maximum contractile response to histamine in the aorta, whereas a concentration (10(-4) M) of NaNP slightly shifted the concentration-response curve for histamine towards its higher concentrations, but did not influence the maximum response in the basilar artery and taenia coli. The reduction in the maximum response of the aorta by NaNP was reversed by removal of the endothelium, or treatment with indomethacin (5 X 10(-6) M) or quinacrine (5 X 10(-6) M), but not by nordihydroguaiaretic acid (NDGA) (5 X 10(-5) M). Prostaglandin (PG) E1, PGE2 and PGI2 produced a relaxation in histamine-contracted basilar artery and taenia coli, whereas PGE1 and PGE2 produced a weak relaxation in histamine-contracted aorta. PGD2 relaxed taenia coli contracted by histamine, but had no influences in aorta and basilar artery. From these results, it is concluded that the inhibitory action of NaNP on histamine-induced contractile response in isolated rabbit aorta may be mediated at least partly by endothelium-derived arachidonic acid metabolite(s) via the cyclooxygenase pathway which must not involve PGI2. Furthermore, the difference in the inhibitory actions of NaNP between the tissues used in this study must be attributed to the absence of such mechanisms both in the basilar artery and taenia coli.

Animals↗
PubMed1986

Mechanisms of inhibitory action of phenylephrine in guinea-pig taenia coli.

The effect of phenylephrine, an alpha-agonist, on the Ca movements and the influence of removal of external Na+ on the relaxant activity of phenylephrine were examined in the taenia coli of guinea pigs. Phenylephrine (10(-7)-10(-5)M) caused dose-dependent relaxation of the taenia coli contracted by 20 mM KCl in Locke-Ringer solution. Phenylephrine (10(-5) M) suppressed the spike discharges of the taenia coli evoked by 20 mM KCl without affecting the membrane potential, and this was accompanied by the muscle relaxation. Phenylephrine also inhibited the cellular 45Ca-uptake in the taenia coli, but had no discernible effect on the 45Ca-efflux from the smooth muscle. These effects of phenylephrine were not observed in a Na-free solution or in the highly depolarized smooth muscle. These findings suggest that the inhibition of Ca-influx in the taenia coli may be involved in the phenylephrine-induced relaxation in the partly depolarized tissue. Reasons for reduction of phenylephrine action encountered under the Na-free condition were also discussed.

Animals↗