RESUMO
Intracellular amino acids (AA) regulate milk protein synthesis within the mammary glands by modifying mammary plasma flow (MPF) and AA transporter activity. Amino acid transporters catalyze translocation using Na+-gradient, substrate gradient (uniporters), and exchange mechanisms; further, they exhibit specificity for individual AA or groups of AA with similar side-chain properties within each transport system. Non-essential AA are actively transported through Na+-dependent transporters and, thus, are often utilized as intracellular currencies for EAA transport through exchange transporters. Therefore, it was hypothesized that individual EAA supplementation would compete with other EAA for shared transporters, and supplementation with Ala, Gln, and Gly would stimulate EAA transport through exchange transporters. Ten primiparous lactating dairy cows were divided into 2 groups based on milk production and were randomly assigned to treatment sequences within 2 balanced 5 × 5 Latin Squares by group. Period length was 14 d. Treatments were 9-d jugular infusions of 1) saline; 2) 34.5 g Val/d; 3) 32.7 g Ala/d: 40 g Gln/d: 26.7 g Gly/d (AQG); 4) 43 g Lys/d; or 5) 33.5 g Ile/d. All cows were fed a common base diet formulated to contain 15.0% CP. Ile, Lys, or AQG infusions did not affect milk protein or milk production; however, Val infusion decreased both. The effects of Val infusion on milk protein production appeared to be partially driven by decreased DMI. The decline in milk protein percentage indicated that milk lactose production was also affected. Additionally, Val infusion increased MPF efficiency (MPF/Milk; L/L) by approximately 44%. Val infusion tended to decrease or decreased mammary net uptakes of Lys, Leu, Met, and total AA. Ile infusion tended to increase its mammary net uptakes but did not affect any other AA. Lys and AQG infusions did not affect any mammary net uptakes. Val infusion tended to decrease Phe and total NEAA mammary clearance rates. AQG infusion stimulated Tyr clearance rates and tended to decline System N mammary clearance rates. Mammary uptake to milk protein output ratios (U:O) of BCAA did not differ from 1 for Val-infused cows, which indicated that little intramammary catabolism was occurring. Additionally, the average NEAA U:O in response to all treatments except Val was 0.70, but Val-infused cows had NEAA U:O that averaged 0.09 indicating increased synthesis within the glands. The effects of Val on mammary net clearance rates of multiple EAA support the incorporation of AA limitations in ration optimizers to prevent AA imbalances. It is possible that over-supplementation of EAA other than Val may also decrease DMI and mammary activity. Identifying efficiency apexes for each of the EAA will allow more precise diet formulation and supplementation, leading to improved production efficiency.
RESUMO
BACKGROUND AND PURPOSE: The extracellular calcium-sensing receptor (CaR) in vascular endothelial cells activates endothelial intermediate-conductance, calcium-sensitive K(+) channels (IK(Ca)) indirectly leading to myocyte hyperpolarization. We determined whether CaR expression and function was modified in a rat model of type II diabetes. EXPERIMENTAL APPROACH: Pressure myography, western blotting, sharp microelectrode and K(+)-selective electrode recordings were used to investigate the functional expression of the CaR and IK(Ca) in rat mesenteric arteries. KEY RESULTS: Myocyte hyperpolarization to the CaR activator calindol was inhibited by Calhex 231. U46619-induced vessel contraction elevated the extracellular [K(+)] around the myocytes, and inhibition of this 'K(+) cloud' by iberiotoxin was needed to reveal calindol-induced vasodilatations. These were antagonized by Calhex 231 and significantly smaller in Zucker diabetic fatty rat (ZDF) vessels than in Zucker lean (ZL) controls. Myocyte hyperpolarizations to calindol were also smaller in ZDF than in ZL arteries. In ZDF vessels, endothelial cell CaR protein expression was reduced; IK(Ca) expression was also diminished, but IK(Ca)-generated hyperpolarizations mediated by 1-EBIO were unaffected. CONCLUSIONS AND IMPLICATIONS: The reduced CaR-mediated hyperpolarizing and vasodilator responses in ZDF arteries result from a decrease in CaR expression, rather than from a modification of IK(Ca) channels. Detection of CaR-mediated vasodilatation required the presence of iberiotoxin, suggesting a CaR contribution to vascular diameter, that is, inversely related to the degree of vasoconstriction. Compromise of the CaR pathway would favour the long-term development of a higher basal vascular tone and could contribute to the vascular complications associated with type II diabetes.
Assuntos
Diabetes Mellitus Tipo 2/fisiopatologia , Artérias Mesentéricas/metabolismo , Canais de Potássio Cálcio-Ativados/metabolismo , Receptores de Detecção de Cálcio/metabolismo , Animais , Western Blotting , Eletrofisiologia , Regulação da Expressão Gênica , Masculino , Artérias Mesentéricas/patologia , Microeletrodos , Células Musculares/metabolismo , Miografia , Ratos , Ratos Wistar , Ratos Zucker , Vasodilatação/fisiologiaRESUMO
BACKGROUND AND PURPOSE: The small and intermediate conductance, Ca2+-sensitive K+ channels (SK(Ca) and IK(Ca), respectively) which are pivotal in the EDHF pathway may be differentially activated. The importance of caveolae in the functioning of IK(Ca) and SK(Ca) channels was investigated. EXPERIMENTAL APPROACH: The effect of the caveolae-disrupting agent methyl-beta-cyclodextrin (MbetaCD) on IK(Ca) and SK(Ca) localization and function was determined. KEY RESULTS: EDHF-mediated, SK(Ca)-dependent myocyte hyperpolarizations evoked by acetylcholine in rat mesenteric arteries (following blockade of IK(Ca) with TRAM-34) were inhibited by MbetaCD. Hyperpolarizations evoked by direct SK(Ca) channel activation (using NS309 in the presence of TRAM-34) were also inhibited by MbetaCD, an effect reversed by cholesterol. In contrast, IK(Ca)-dependent hyperpolarizations (in the presence of apamin) were unaffected by MbetaCD. Similarly, in porcine coronary arteries, EDHF-mediated, SK(Ca)-dependent (but not IK(Ca)-dependent) endothelial cell hyperpolarizations evoked by substance P were inhibited by MbetaCD. In mesenteric artery homogenates subjected to sucrose-density centrifugation, caveolin-1 and SK3 (SK(Ca)) proteins but not IK1 (IK(Ca)) protein migrated to the buoyant, caveolin-rich fraction. MbetaCD pretreatment redistributed caveolin-1 and SK3 proteins into more dense fractions. In immunofluorescence images of porcine coronary artery endothelium, SK3 (but not IK1) and caveolin-1 were co-localized. Furthermore, caveolin-1 immunoprecipitates prepared from native porcine coronary artery endothelium contained SK3 but not IK1 protein. CONCLUSIONS AND IMPLICATIONS: These data provide strong evidence that endothelial cell SK(Ca) channels are located in caveolae while the IK(Ca) channels reside in a different membrane compartment. These studies reveal cellular organisation as a further complexity in the EDHF pathway signalling cascade.
Assuntos
Artérias/efeitos dos fármacos , Fatores Biológicos/fisiologia , Cavéolas/fisiologia , Canais de Potássio Cálcio-Ativados/fisiologia , beta-Ciclodextrinas/farmacologia , Acetilcolina/farmacologia , Animais , Artérias/citologia , Artérias/fisiologia , Western Blotting , Cavéolas/metabolismo , Caveolinas/metabolismo , Vasos Coronários/citologia , Vasos Coronários/efeitos dos fármacos , Vasos Coronários/fisiologia , Relação Dose-Resposta a Droga , Endotélio Vascular/fisiologia , Técnicas In Vitro , Indóis/farmacologia , Masculino , Potenciais da Membrana/efeitos dos fármacos , Artérias Mesentéricas/citologia , Artérias Mesentéricas/efeitos dos fármacos , Artérias Mesentéricas/fisiologia , Oximas/farmacologia , Canais de Potássio Cálcio-Ativados/antagonistas & inibidores , Canais de Potássio Cálcio-Ativados/metabolismo , Pirazóis/farmacologia , Ratos , Ratos Wistar , Suínos , Vasodilatadores/farmacologiaRESUMO
Seven groups of synthetic agent, distinguished by a combination of their chemical and pharmacological characteristics exert some or all of their effects by opening plasmalemmal K+ channels primarily in smooth muscle. Progress over the past two years now allows broad structure-activity relationships to be formulated within many of the individual groups of agent. Gillian Edwards and Arthur Weston review the historical basis of these discoveries and comment on the significance of new developments. They focus on the search for tissue and channel selectivity, two factors likely to be important for the successful clinical deployment of these substances as antihypertensive and bronchodilator agents.
Assuntos
Canais de Potássio/efeitos dos fármacos , Animais , Humanos , Relação Estrutura-AtividadeRESUMO
Potassium channel openers comprise a diverse group of chemical agents which open plasma-lemmal K-channels. They show selectivity for smooth muscle, although K-channels in cardiac and skeletal muscle, neurones and the pancreatic beta-cell are also affected at relatively high concentrations. In addition, at least one endogenous K-channel opener of vascular origin--endothelium-derived hyperpolarizing factor--exists and in man plays a role in modulating blood vessel tone. The type of K-channel involved in the actions of both exogenous and endogenous K-channel openers is still uncertain, although a prime candidate in smooth muscle seems similar to the [ATPi]-modulated K-channel in the pancreatic beta-cell. This review focuses attention on the action of these agents in vascular smooth muscle and on the possible clinical exploitation of their powerful vasorelaxant properties.
Assuntos
Músculo Liso/efeitos dos fármacos , Canais de Potássio/efeitos dos fármacos , Animais , Humanos , Músculo Liso/fisiologiaRESUMO
1. Simultaneous measurements of oxygen consumption and mechanical activity have been made in isolated preparations of guinea-pig taenia coli, rabbit abdominal aorta and the longitudinal muscle of rabbit duodenum.2. Mean resting oxygen consumption was greater in mechanically-active preparations (taenia coli and duodenum) than in the aorta which showed no spontaneous activity.3. The relaxation produced by isoprenaline in guinea-pig taenia coli and rabbit duodenum was accompanied by a dose-dependent fall in oxygen consumption.4. The relaxation produced by phenylephrine in guinea-pig taenia coli was accompanied by a dose-dependent fall in oxygen consumption whereas, in the rabbit duodenum, the transient fall in tension was not accompanied by any significant change in oxygen consumption.5. The increase in tension produced by phenylephrine in rabbit abdominal aorta was accompanied by an increase in oxygen consumption.6. Changes in mechanical activity and oxygen consumption produced by isoprenaline and phenylephrine were antagonized by propranolol and phentolamine respectively.7. It is concluded that the variations in oxygen consumption associated with spontaneous or drug-induced mechanical changes are simple reflections of altered mechanical activity. The possibility of additional direct metabolic actions of isoprenaline and phenylephrine is discussed.
Assuntos
Isoproterenol/farmacologia , Músculo Liso/metabolismo , Consumo de Oxigênio/efeitos dos fármacos , Fenilefrina/farmacologia , Animais , Aorta Abdominal/efeitos dos fármacos , Colo/efeitos dos fármacos , Duodeno/efeitos dos fármacos , Cobaias , Técnicas In Vitro , Isoproterenol/antagonistas & inibidores , Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Fentolamina/farmacologia , Fenilefrina/antagonistas & inibidores , Propranolol/farmacologia , CoelhosRESUMO
1. Inhibition of mechanical activity in longitudinal muscle strips of rabbit duodenum was induced by perivascular and intramural nerve stimulation.2. The effects of perivascular stimulation were abolished by phentolamine + propranolol, guanethidine, reserpine and by tetrodotoxin. The effects of intramural stimulation were abolished only by tetrodotoxin.3. Noradrenaline, phenylephrine, isoprenaline, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and adenosine each produced an inhibition of mechanical activity. The relative potencies of these agonists were noradrenaline>isoprenaline>phenylephrine>ATP>ADP>adenosine>AMP.4. Exposure of tissues to high concentrations of either ATP or adenosine desensitized the tissue to further exposure to ATP, ADP, AMP and adenosine, whilst the inhibitory effects of noradrenaline, phenylephrine and isoprenaline and of perivascular and intramural stimulation were unaffected. The effects of desensitization were reversible.5. It was concluded that the effects of intramural stimulation were mediated neither by noradrenaline nor by adenosine or its derivatives.
Assuntos
Adenosina/farmacologia , Duodeno/fisiologia , Contração Muscular/efeitos dos fármacos , Difosfato de Adenosina/farmacologia , Monofosfato de Adenosina/farmacologia , Trifosfato de Adenosina/farmacologia , Animais , Atropina/farmacologia , Dessensibilização Imunológica , Relação Dose-Resposta a Droga , Duodeno/efeitos dos fármacos , Estimulação Elétrica , Técnicas In Vitro , Isoproterenol/farmacologia , Músculo Liso/efeitos dos fármacos , Norepinefrina/farmacologia , Fentolamina/farmacologia , Fenilefrina/farmacologia , Propranolol/farmacologia , Coelhos , Reserpina/farmacologia , Relação Estrutura-Atividade , Tetrodotoxina/farmacologiaRESUMO
Contractions of the longitudinal muscle of guinea-pig ileum were inhibited by adenosine triphosphate. This inhibition was prevented by specific desensitization of the tissue to adenosine triphosphate whilst the peristaltic reflex was unaffected. The results suggest that the transmitter substance released from the intramural inhibitory neurones activated during peristalsis is not adenosine triphosphate.
Assuntos
Trifosfato de Adenosina/farmacologia , Motilidade Gastrointestinal/efeitos dos fármacos , Acetilcolina/farmacologia , Animais , Dessensibilização Imunológica , Cobaias , Compostos de Hexametônio/farmacologia , Íleo/efeitos dos fármacos , Técnicas In Vitro , Contração Muscular/efeitos dos fármacos , Norepinefrina/farmacologia , Reflexo/efeitos dos fármacosRESUMO
1. Tension changes produced by phenylephrine and isoprenaline have been examined in four tissues-the guinea-pig taenia coli, the longitudinal muscle strip of rabbit duodenum, the abdominal aorta of the rabbit and the rat heart.2. Changes in the amounts of adenosine triphosphate (ATP), creatine phosphate (CP) and glucose-6-phosphate (G-6-P) associated with the addition of phenylephrine and isoprenaline have been measured in the four tissues using enzymatic fluorimetric analysis.3. An alpha-adrenoceptor-mediated increase in tension (phenylephrine; rabbit aorta) was associated with no change in the amounts of ATP, CP or G-6-P.4. An alpha-adrenoceptor-mediated decrease in tension (phenylephrine; guineapig taenia coli and rabbit duodenum) was associated with no change in the amounts of ATP, CP or G-6-P.5. A beta-adrenoceptor-mediated increase in force of contraction (phenylephrine and isoprenaline; rat heart) was associated with a reduction in the amounts of ATP and CP and an increase in the amount of G-6-P.6. A beta-adrenoceptor-mediated decrease in tension (isoprenaline; guinea-pig taenia coli and rabbit duodenum) was associated with an increase in the amounts of ATP and CP and no change in the amount of G-6-P.7. beta-Adrenoceptor-mediated metabolic changes were antagonized by propranolol.
Assuntos
Coração/efeitos dos fármacos , Isoproterenol/farmacologia , Músculo Liso/efeitos dos fármacos , Fenilefrina/farmacologia , Fosfatos/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Aorta Abdominal/efeitos dos fármacos , Colo/efeitos dos fármacos , Duodeno/efeitos dos fármacos , Feminino , Glucose/metabolismo , Glucofosfatos/metabolismo , Cobaias , Hexosefosfatos/metabolismo , Técnicas In Vitro , Masculino , Contração Muscular , Músculo Liso/metabolismo , Miocárdio/metabolismo , Fosfocreatina/metabolismo , Coelhos , Ratos , Receptores AdrenérgicosRESUMO
1 Hyoscine- and guanethidine-treated preparations of longitudinal muscle of rabbit duodenum, guinea-pig taenia caeci and fundic strip relaxed when exposed to noradrenaline, adenosine, adenosine triphosphate (ATP) or to field stimulation of their intramural nerves. 2 In guinea-pig taenia caeci and fundus, theophylline 100 mumol/l had no effect on responses to noradrenaline, adenosine, ATP and intramural nerve stimulation. 3 In rabbit duodenum, theophylline 100 mumol/l antagonized some responses to adenosine but had no effect on responses to noradrenaline, ATP and intramural nerve stimulation. 4 Theophylline 1 mmol/l itself relaxed the intestinal tissues and in the fundic strip and taenia caeci, these relaxant effects were associated with abolition of spike activity and cellular hyperpolarization. In the taenia caeci, the amplitude of inhibitory post-junctional potentials was reduced. 5 Theophylline 1 mmol/l antagonized the twitch suppression produced by adenosine and ATP in the transmurally-stimulated guinea-pig ileum but not that evoked by noradrenaline. 6 It is concluded that theophylline can selectively antagonize some actions of purines in the intestine but that it does not specifically antagonize the effect of intramural inhibitory nerve stimulation.
Assuntos
Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Purinas/antagonistas & inibidores , Teofilina/farmacologia , Animais , Estimulação Elétrica , Feminino , Cobaias , Técnicas In Vitro , Intestinos/efeitos dos fármacos , Intestinos/inervação , Masculino , Potenciais da Membrana/efeitos dos fármacos , CoelhosRESUMO
BRL 34915 (4-64 X 10(-7) M), isoprenaline (0.5-32 X 10(-8) M) and nicorandil (4-64 X 10(-6) M) produced a slowly-developing relaxation of spontaneous tone of the guinea-pig taenia caeci; with no after-contraction on washout. These inhibitory responses were unaffected by apamin (10(-7) M). Adenosine triphosphate (0.06-2 X 10(-3) M) and noradrenaline (1-16 X 10(-7) M) produced a rapid inhibition of spontaneous tone with a prominent after-contraction, especially on washout. Both the inhibitory effect and the rebound contraction were abolished by apamin (10(-7) M). Exposure to both BRL 34915 (64 X 10(-7) M) and to nicorandil (64 X 10(-6) M) produced an increase in the 86Rb efflux rate coefficient which was unaffected by apamin (10(-7) M). Exposure to isoprenaline (32 X 10(-8) M) had no effect on the 86Rb efflux rate coefficient. Exposure to noradrenaline (16 X 10(-7) M) produced an increase in the 86Rb efflux rate coefficient which was abolished by apamin (10(-7) M). The results confirm that both BRL 34915 and nicorandil are capable of opening potassium channels in smooth muscle but show that the channel is not apamin-sensitive.
Assuntos
Anti-Hipertensivos/farmacologia , Apamina/farmacologia , Venenos de Abelha/farmacologia , Benzopiranos/farmacologia , Relaxantes Musculares Centrais/farmacologia , Músculo Liso/efeitos dos fármacos , Niacinamida/análogos & derivados , Pirróis/farmacologia , Trifosfato de Adenosina/farmacologia , Animais , Ceco/efeitos dos fármacos , Cromakalim , Feminino , Cobaias , Técnicas In Vitro , Canais Iônicos/efeitos dos fármacos , Isoproterenol/farmacologia , Masculino , Tono Muscular/efeitos dos fármacos , Niacinamida/farmacologia , Nicorandil , Norepinefrina/farmacologiaRESUMO
The effects of the antihypertensive agent BRL 34915 on a variety of responses of the aorta and portal vein of the rat have been compared with those of nicorandil. On portal vein, BRL 34915 (0.01-50 X 10(-6) M) and nicorandil (0.1-500 X 10(-6) M) abolished spontaneous mechanical activity and reduced mechanical responses to noradrenaline (0.1-100 X 10(-6) M) and K+ (5-20 X 10(-3) M) but had little inhibitory effect on responses to K+ (40-80 X 10(-3) M). The onset of the reduced responses to noradrenaline was delayed by both agents. On portal vein, BRL 34915 (0.1-50 X 10(-6) M) and nicorandil (0.5-500 X 10(-6) M) abolished spontaneous electrical and mechanical activity, hyperpolarized the smooth muscle cells to a value close to their calculated potassium equilibrium potential and increased the 86Rb efflux rate coefficient. On aorta, BRL 34915 (0.2-0.8 X 10(-6) M) and nicorandil (8-32 X 10(-6) M) reduced mechanical responses to noradrenaline (0.001-1 X 10(-6) M) and K+ (5-20 X 10(-3) M) but had little inhibitory effect on responses to K+ (40-80 X 10(-3) M). On aorta, BRL 34915 (0.2-0.8 X 10(-6) M) increased the 86Rb efflux rate coefficient whereas nicorandil (8-32 X 10(-6) M) was without effect. It is concluded that the inhibitory actions of BRL 34915 on both aorta and portal vein result from the opening of membrane potassium channels. The resulting membrane shunt inhibits the effects of excitatory agents. The inhibitory effects of nicorandil result from a combination of the opening of potassium channels together with an additional, undefined action.
Assuntos
Anti-Hipertensivos/farmacologia , Benzopiranos/farmacologia , Músculo Liso Vascular/metabolismo , Niacinamida/análogos & derivados , Pirróis/farmacologia , Animais , Aorta Torácica/efeitos dos fármacos , Cromakalim , Técnicas In Vitro , Canais Iônicos/efeitos dos fármacos , Masculino , Potenciais da Membrana/efeitos dos fármacos , Músculo Liso Vascular/efeitos dos fármacos , Niacinamida/farmacologia , Nicorandil , Norepinefrina/farmacologia , Veia Porta/efeitos dos fármacos , Radioisótopos , Ratos , Ratos Endogâmicos , Rubídio , Fatores de TempoRESUMO
In insulinoma cells (RINm5F), the glibenclamide-sensitive K-current (IK(ATP)) which developed spontaneously or after exposure to levcromakalim or to butanedione monoxime was always accompanied by a reduction in the delayed rectifier current (IK(V)). At potentials over which IK(V) was fully activated, the total outward current remained constant. In rat portal vein, the delayed rectifier channel inhibitor, margatoxin, reduced the combined induction of IK(ATP) and inhibition of IK(V) by levcromakalim. These data suggest that the ATP-sensitive K-channel, K(ATP), is a voltage-insensitive state of the delayed rectifier, KV.
Assuntos
Glibureto/farmacologia , Canais de Potássio/fisiologia , Animais , Benzopiranos/farmacologia , Cromakalim , Insulinoma/metabolismo , Neurotoxinas/farmacologia , Fosforilação , Veia Porta/efeitos dos fármacos , Veia Porta/metabolismo , Canais de Potássio/efeitos dos fármacos , Pirróis/farmacologia , Ratos , Venenos de Escorpião , Células Tumorais CultivadasRESUMO
1. In a physiological salt solution (PSS) in which potassium (K) was replaced by rubidium (Rb), segments of rat aorta precontracted with 20 mM RbCl were fully relaxed by K-channel openers with an order of potency levcromakalim > cromakalim > aprikalim > RP 49356. These relaxations were inhibited by glibenclamide. 2. Segments of rat aorta bathed in normal PSS and precontracted with 20 mM KCl were also relaxed by these K-channel openers with an order of potency levcromakalim > cromakalim > aprikalim > RP 49356. These relaxations were glibenclamide-sensitive. However, the absolute potencies of the K-channel openers were approximately four times greater in normal PSS than in RbPSS. 3. In RbPSS, minoxidil sulphate relaxed segments of aorta precontracted with 20 mM RbCl by approximately 20% whereas in normal PSS it fully relaxed those contracted with 20 mM KCl. 4. In RbPSS, levcromakalim-induced relaxation of aortic segments precontracted with 20 mM RbCl was initially well-maintained but then faded by approximately 60% of the initial relaxation to a new, stable level. Subsequent exposure to RP 49356 or to higher concentrations of levcromakalim was without further relaxant effect. Similar changes were observed when RP 49356 was the initial relaxant and tissues were exposed to either RP 49356 or levcromakalim. In normal PSS, levcromakalim- or RP 49356-induced relaxation of contractions produced by 20 mM KCl was well-maintained. 5. In RbPSS, minoxidil sulphate-induced relaxation of aortic segments precontracted with 20 mM RbCl was well-maintained. Subsequent exposure to either levcromakalim or to RP 49356 produced further tissue relaxation. 6. In RbPSS, levcromakalim produced no detectable increase in either 86Rb- or 42K-efflux from rat aortic strips. In normal PSS, a significant increase in the exchange of both isotopes was detected.7. Levcromakalim hyperpolarized segments of rat aorta bathed both in normal PSS and after depolarization by the addition of 20 mM KCI. Exposure to RbPSS depolarized the tissue and under these conditions, levcromakalim had no effect on membrane potential.8. In Rb- and normal PSS, levcromakalim produced a similar degree of inhibition of the refilling of then or adrenaline-sensitive Ca store.9. It is concluded that millimolar concentrations of Rb inhibit the plasmalemmal ATP-sensitive K-channels (KATP) which are the target of the K-channel openers. The relaxant actions of the K-channel openers in both normal and Rb-PSS and the inhibition of these effects by glibenclamide may reflect a functional interaction between these agents at ATP-binding sites associated with both KATP and with intracellular structures including Ca stores.
Assuntos
Músculo Liso Vascular/metabolismo , Canais de Potássio/efeitos dos fármacos , Rubídio/farmacologia , Animais , Anti-Hipertensivos/farmacologia , Aorta Torácica/efeitos dos fármacos , Aorta Torácica/metabolismo , Benzopiranos/farmacologia , Cromakalim , Técnicas In Vitro , Masculino , Microeletrodos , Relaxamento Muscular/efeitos dos fármacos , Músculo Liso Vascular/efeitos dos fármacos , Picolinas/farmacologia , Veia Porta/efeitos dos fármacos , Veia Porta/metabolismo , Cloreto de Potássio/farmacologia , Radioisótopos de Potássio , Piranos/farmacologia , Pirróis/farmacologia , Ratos , Ratos Sprague-Dawley , Radioisótopos de Rubídio , Taquifilaxia/fisiologia , Vasodilatadores/farmacologiaRESUMO
Guinea-pig colon was shown to contain both alpha- and beta-adrenoceptors. Isoprenaline-induced relaxation was mediated by beta-adrenoceptors alone whilst that produced by phenylephrine was mediated by both alpha- and beta- adrenoceptors.
Assuntos
Colo/efeitos dos fármacos , Receptores de Droga , Animais , Cobaias , Técnicas In Vitro , Isoproterenol/antagonistas & inibidores , Isoproterenol/farmacologia , Contração Muscular/efeitos dos fármacos , Fentolamina/farmacologia , Fenilefrina/antagonistas & inibidores , Propranolol/farmacologia , Receptores AdrenérgicosRESUMO
1 Strips of longitudinal muscle from rabbit intestine accumulated radioactivity when exposed to [(3)H]-adenosine.2 Accumulation of radioactivity was not sodium-dependent or ouabain-sensitive, but was reduced by cooling, zero glucose plus bubbling with N(2), 2,4,dinitrophenol, dipyridamole, hexobendine and lidoflazine.3 After 7 min exposure to [(3)H]-adenosine, the tissue was found to contain radioactive adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and adenosine itself in the approximate ratio 13: 6: 4: 1.4 In the presence of dipyridamole, hexobendine or lidoflazine (each 1 muM), the amounts of radioactive ATP, ADP, AMP and adenosine were reduced with the concentration of adenosine not significantly different from controls.5 It is concluded that energy-dependent uptake of adenosine does not occur in the longitudinal muscle of rabbit intestine. Adenosine enters the tissue by a passive process and rapidly becomes phosphorylated giving rise to apparently high tissue: medium ratios.6 The drugs dipyridamole, hexobendine and lidoflazine appear to reduce the accumulation of radioactivity by preventing the formation of adenosine phosphate derivatives.
Assuntos
Adenosina/metabolismo , Mucosa Intestinal/metabolismo , Músculo Liso/metabolismo , Animais , Benzoatos/farmacologia , Temperatura Baixa , Dinitrofenóis/farmacologia , Dipiridamol/farmacologia , Relação Dose-Resposta a Droga , Duodeno/metabolismo , Metabolismo Energético , Etilenodiaminas/farmacologia , Glucose/farmacologia , Técnicas In Vitro , Intestinos/efeitos dos fármacos , Cinética , Lidoflazina/farmacologia , Ouabaína/farmacologia , CoelhosRESUMO
Some of the effects of dipyridamole, hexobendine and lidoflazine on mechanical responses in rabbit duodenum have been investigated. In concentrations known to inhibit tissue accumulation of adenosine and its metabolites, none of these agents potentiated inhibitory responses to intramural nerve stimulation or to application of adenosine, adenosine triphosphate or phenylephrine. These results neither support nor dispute the suggestion that adenosine or a related nucleotide is the intramural inhibitory transmitter but do show that tissue accumulation in rabbit duodenum is not an important feature in the termination of the action of adenosine.
Assuntos
Benzoatos/farmacologia , Dipiridamol/farmacologia , Duodeno/efeitos dos fármacos , Lidoflazina/farmacologia , Piperazinas/farmacologia , Adenosina/metabolismo , Adenosina/farmacologia , Trifosfato de Adenosina/farmacologia , Animais , Atropina/farmacologia , Relação Dose-Resposta a Droga , Sinergismo Farmacológico , Duodeno/fisiologia , Estimulação Elétrica , Etilenodiaminas/farmacologia , Técnicas In Vitro , Contração Muscular/efeitos dos fármacos , Fentolamina/farmacologia , Fenilefrina/farmacologia , Potenciometria , Propranolol/farmacologia , CoelhosRESUMO
1 The effect of potassium channel opening compounds has been investigated in the smooth muscle of rabbit aorta under Ca-free conditions. Examination of the characteristics of the response has been performed using cromakalim as the prototype compound. 2 In order of potency, Ro 31-6930, cromakalim, minoxidil sulphate and pinacidil each produced a contraction in rabbit aortic strips bathed in Ca-free MOPS-buffered physiological salt solution (PSS). In contrast, forskolin, glyceryl trinitrate and nifedipine each failed to increase tension under identical conditions. Cromakalim also evoked contraction of bovine trachealis muscle bathed in Ca-free PSS. 3. The contractile response to cromakalim in rabbit aortic strips was of delayed onset (15-20 min) and reached a plateau after approximately 120 min (1.8 g maximum with 1 microM cromakalim). No cromakalim-induced tension changes were observed in either 1 mM or 2.5 mM Ca-containing PSS. 4. Raising the [KCl] of the Ca-free PSS to 65.9 mM fully inhibited the cromakalim-induced contraction in rabbit aortic strips. In addition, pretreatment of aortic strips with the sulphonylurea glibenclamide antagonized the subsequent mechanical response to cromakalim. 5. In Ca-free PSS, cromakalim (1 microM) stimulated 42K-efflux with a time-course corresponding to the contractile event. Glibenclamide (1 microM) inhibited this cromakalim-induced 42K-efflux. 6. In sharp microelectrode studies in bovine trachealis, cromakalim (10 microM) produced a sustained membrane hyperpolarization in normal PSS. In contrast, the cromakalim-induced hyperpolarization in Ca-free PSS was not sustained. The fading of the hyperpolarization was temporally correlated with the increase in tension under these experimental conditions. 7. It is concluded that the K-channel opener-induced smooth muscle contractile response revealed in Ca-free PSS is the consequence of K-channel opening. The nature of the detailed mechanism which underlies this contractile phenomenon remains to be determined.
Assuntos
Benzopiranos/farmacologia , Cálcio/metabolismo , Músculo Liso Vascular/efeitos dos fármacos , Canais de Potássio/efeitos dos fármacos , Pirróis/farmacologia , Vasoconstrição/efeitos dos fármacos , Animais , Aorta/efeitos dos fármacos , Colforsina/farmacologia , Cromakalim , Guanidinas/farmacologia , Masculino , Microeletrodos , Minoxidil/farmacologia , Contração Muscular/efeitos dos fármacos , Nifedipino/farmacologia , Nitroglicerina/farmacologia , Pinacidil , Potássio/metabolismo , Piridinas/farmacologia , CoelhosRESUMO
1. The mechanism of the manganese-induced spasm of the guinea-pig ileum was investigated using agents known to modify nerve function. The spasm was reduced by cooling, tetrodotoxin, procaine, Botulinus toxin (Type A), hyoscine and pempidine. It was potentiated by mipafox.2. In the presence of manganese, the release of acetylcholine from the ileum was greatly increased.3. Tetrodotoxin prevented the manganese-induced increase in acetylcholine output from the ileum but had no significant effect on the spontaneous acetylcholine output.4. It is suggested that the manganese-induced spasm of the ileum results from an action on intramural cholinergic nerves.
Assuntos
Íleo/efeitos dos fármacos , Manganês/farmacologia , Acetilcolina/metabolismo , Animais , Inibidores da Colinesterase/farmacologia , Clostridium botulinum , Temperatura Baixa , Estimulação Elétrica , Cobaias , Íleo/inervação , Técnicas In Vitro , Pempidina/farmacologia , Nervos Periféricos/efeitos dos fármacos , Procaína/farmacologia , Escopolamina/farmacologia , Tetrodotoxina/farmacologia , Toxinas Biológicas/farmacologiaRESUMO
1 The effects of methoxyverapamil (D600), nifedipine and sodium nitroprusside on noradrenaline-induced electrical and mechanical activity in rat portal vein have been examined. 2 D600 and nifedipine produced a concentration-dependent reduction in mechanical responses to noradrenaline whilst sodium nitroprusside had no effect. The effects of D600 and nifedipine were reversed by increasing the extracellular calcium concentration. 3 The mechano-inhibitory effects of D600 were accompanied by a marked reduction in electrical activity with some evidence of electromechanical uncoupling. 4 The mechano-inhibitory effects of nifedipine were associated with considerable electromechanical uncoupling. 5 It is concluded that in the concentrations used, D600 acts primarily by inhibiting calcium influx with some effect on electromechanical coupling whilst nifedipine interferes mainly with the coupling process. The inactivity of sodium nitroprusside suggests that the excitation-contraction coupling process in rat portal vein is relatively simple and further studies with this tissue seem indicated.