Biomedical subjects

S Kigoshi

Publications and source records attributed to S Kigoshi.

At least 55 records · Page 3Linked to original sources

PubMed1990

Electrophysiological and mechanical effects of calcitonin gene-related peptide on guinea-pig atria.

1. The effects of calcitonin gene-related peptide (CGRP) on mechanical and electrophysiological responses were studied in the guinea-pig atrial muscle preparations and in single cells. 2. CGRP (greater than 10(-9) M) enhanced the twitch contraction in a concentration-dependent manner in electrically driven left atria and increased heart rate in spontaneously beating right atria. The positive inotropic and chronotropic effects of CGRP were not inhibited by propranolol but were attenuated by reduction of the calcium concentration in the bathing medium. 3. In single left atrial cells, CGRP slightly hyperpolarized the resting potential but did not affect the other action potential parameters significantly. 4. Under whole-cell voltage-clamp conditions, CGRP increased the calcium inward current. The peptide also increased the steady inward current elicited by hyperpolarization and the late outward current by depolarization. 5. These results suggest that CGRP may produce the positive inotropic and presumably chronotropic effects by increasing calcium inward current. CGRP also increases the potassium permeability. Such effects on ionic currents may not produce any apparent change in the action potential conformation, due to their opposite directional actions and relatively weak potencies.

Action Potentials↗

PubMed1990

Somatostatin decreases the calcium inward current in guinea-pig atria.

1. The effects of somatostatin on mechanical and electrophysiological responses were studied in guinea-pig atrial muscle preparations and single cells. 2. Somatostatin (greater than or equal to 10(-8) M) decreased the twitch contraction in a concentration-dependent manner in electrically driven left atria and spontaneously beating right atria. However, the beating rate was not affected. 3. The negative inotropic effect of somatostatin was transient. Desensitization to this agent developed slowly during continuous exposure to the peptide. 4. In single atrial cells, somatostatin significantly shortened the action potential duration, but the resting potential and action potential amplitude were not affected. 5. Under whole cell voltage-clamp conditions, somatostatin decreased the calcium inward current without affecting the sodium and potassium currents. 6. These results suggest that somatostatin selectively acts on the calcium channel of guinea-pig atrial cells to reduce the calcium inward current, which in turn gives rise to the negative inotropic effect.

Action Potentials↗

PubMed1990

Two distinct alpha 1-adrenoceptor subtypes involved in noradrenaline contraction of the rabbit thoracic aorta.

1. Recently, alpha 1-adrenoceptors in blood vessels have been classified into three subtypes (alpha 1H, alpha 1L and alpha 1N). We examined which subtype (or subtypes) is involved in the noradrenaline-induced contraction of rabbit thoracic aorta. 2. Noradrenaline produced a concentration-dependent contraction in the rabbit isolated thoracic aorta. Prazosin antagonized the contractions to noradrenaline, resulting in a rightward displacement of the concentration-response curve. However, the shift was not proportional to the concentration of prazosin; Schild plots showed that the inhibition by prazosin was biphasic, implying that noradrenaline acted through two receptor populations. Two affinity constants (pKB values of 10.02 and 8.83) were determined for prazosin at these sites. 3. However, under continuous treatment with 1 nM prazosin, or in strips pretreated with chlorethylclonidine (CEC; an alpha 1H inactivating agent) to remove the contribution of one receptor population, prazosin showed a single pKB or pA2 value of approximately 8.3. 4. Yohimbine also produced biphasic antagonism of noradrenaline-induced contractions, resulting in two affinity constants (pKB = 6.52 and 6.17). However, a monophasic Schild plot was obtained for yohimbine either in the presence of 1 nM prazosin (pA2 = 6.08) or in strips pretreated with CEC (pA2 = 6.03). 5. The Schild plot for HV723 (a selective alpha 1N-antagonist) yielded a monophasic slope (pKB = 8.47) and the inhibition was not affected by 1 nM prazosin or CEC-pretreatment. 6. [3H]-prazosin bound to alpha 1-adrenoceptors of the aortic membrane preparations with two different affinities (pKD = 9.94 and 8.37). The high but not the low affinity site was completely masked by 1 nM prazosin and inactivated by pretreatment with CEC. 7. These results strongly suggest that noradrenaline-induced contraction of the rabbit thoracic aorta is mediated through two distinct alpha l-adrenoceptor subtypes, designated alpha 1H and (alpha lL*

Acetonitriles↗

PubMed1990

Pharmacological subclassification of alpha 1-adrenoceptors in vascular smooth muscle.

1. We examined whether alpha 1-adrenoceptors in various blood vessels can be divided into subtypes by antagonist affinity or by susceptibility to chloroethylclonidine or nifedipine. 2. Noradrenaline or phenylephrine produced concentration-dependent contractions in all the tissues tested, which were competitively inhibited by phentolamine, yohimbine, prazosin, WB4101 and HV723. However, there were large differences between the tissues in the pA2 values for all the antagonists except phentolamine. 3. The blood vessels could be classified into three groups (I, II and III) on the basis of their affinity variation. In group I (dog mesenteric artery and vein, saphenous vein), the pA2 values for HV723 were greater than 9, and those for HV723 and WB4101 were approximately 1 log unit higher than for prazosin. This rank order of affinity reversed in group II (dog carotid artery and rat thoracic aorta), where prazosin was more potent (pA2 values greater than 9.5) than HV723 or WB4101. In group III (rabbit mesenteric artery, thoracic aorta and carotid artery and guinea-pig thoracic aorta), on the other hand, prazosin, HV723 and WB4101 inhibited the noradrenaline response with a similar affinity (pA2 values ranging from 8 to 9). 4. Yohimbine inhibited the responses to noradrenaline and phenylephrine with a lower affinity than prazosin, HV723 or WB4101. The pA2 values for yohimbine were similar in groups I and II (the values greater than 6.5), which were greater than those in group III (values less than 6.4). 5. The alpha l-adrenoceptors in group II were selectively affected by chlorethylclonidine, resulting in an irreversible attenuation of noradrenaline responses in the dog carotid artery and a persistent contraction in the rat thoracic aorta. 6. Nifedipine either produced no effect or a slight inhibition of alpha l-adrenoceptor-mediated contractions in all the blood vessels; these effects were not correlated to the above groups. 7. These results suggest that alpha,-adrenoceptors of blood vessels can be divided into three subtypes (designated as alpha 1H, alpha4L and alpha 1N) by antagonist affinity and their susceptibility to chloroethylclonidine but not to nifedipine: the characteristics of each subtype are summarized in Table 3. Subtypes alpha lH, alpha 1L and alpha lN may be predominantly involved in the contractile responses to noradrenaline or phenylephrine of the blood vessels in groups II, III and I, respectively.

Acetonitriles↗

PubMed1990

Dissociation between sympathetic purinergic response and ATP response in the mesenteric artery of the dog.

In the presence of prazosin and propranolol, electrical transmural stimulation of isolated dog mesenteric artery produced a sympathetic purinergic contraction, which was followed by a relaxation in PGF2 alpha-contracted arteries. Such purinergic responses were mimicked by brief exposure to alpha, beta-methylene ATP (alpha, beta-Me ATP) and were completely inhibited after desensitization of P2x-purinergic receptors. However, exogenous ATP predominantly evoked a relaxation in PGF2 alpha-contracted artery. These results suggest that the sympathetic purinergic response may be caused by a P2x-purinergic receptor-selective mechanism or substance, rather than ATP.

Adenosine Triphosphate↗

PubMed1990

Novel cardioprotective effects of TYB-3823 on ischemic damage in the working hearts of rats: comparison with lidocaine.

The cardioprotective effects of a new antiarrhythmic drug, TYB-3823 [1-(2,6-dimethylphenyl)-dimethylaminoguanidine hydrochloride] were examined in the working hearts of rats and compared with those of lidocaine. Before ischemia, TYB-3823 at 5 x 10(-5) M produced a slight negative inotropic effect, resulting in a decrease in aortic flow and cardiac output. However, at lower concentrations (10(-6) and 10(-5) M), the drug had no significant effect on the functional cardiac parameters before ischemia. Lidocaine at such concentrations also had no effect. Global ischemia for 15 min decreased cardiac function rapidly which only recovered partially, with a delay, after reperfusion in the control hearts. Treatment with TYB-3823 accelerated the time course of recovery during reperfusion markedly, significantly improving functional cardiac parameters. However, lidocaine had little effect on recovery of function. Reperfusion-induced arrhythmia was equipotently inhibited by TYB-3823 and lidocaine. Leakage of cytosolic enzymes (lactate dehydrogenase, creatine phosphokinase and alpha-hydroxybutylic dehydrogenase) during reperfusion was inhibited more effectively by TYB-3823 than lidocaine. Light microscopic and electron microscopic examinations revealed that treatment with TYB-3823 protected against the histological damage induced by ischemia, such as hyaline degeneration of myocardium, absence of cross-striation and swelling of mitochondria. These results suggest that, unlike lidocaine, TYB-3823 causes a novel cardioprotective effect through unknown mechanisms in addition to its antiarrhythmic action.

Animals↗

PubMed1989

Selective inhibition by nifedipine of the purinergic component of neurogenic vasoconstriction in the dog mesenteric artery.

The neurogenic contractions evoked by perivascular sympathetic nerve stimulation of dog mesenteric artery consist of purinergic and adrenergic components, and these components were selectively inhibited by alpha, beta-methylene ATP and prazosin, respectively. We examined the effects of Ca antagonists on both these components in dog mesenteric arteries. Nifedipine (10(-8)-10(-6) M) inhibited the purinergic and adrenergic contractions evoked by transmural electrical stimulation, and this inhibition was more evident for the purinergic component of the response. Nifedipine was also more potent to inhibit the contractile response to alpha, beta-methylene ATP than it was to inhibit the responses to noradrenaline. Verapamil and diltiazem also inhibited the purinergic and adrenergic responses induced by transmural electrical stimulation, alpha, beta-methylene ATP or noradrenaline, but the extend of the inhibition was less than that seen with nifedipine. These three Ca antagonists had little effect on the 3H efflux evoked by electrical transmural stimulation of arteries that had been preincubated with [3H]noradrenaline. These results show that nifedipine is a selective inhibitor of the purinergic component of contractions evoked by sympathetic nerve stimulation of blood vessels.

Adenosine Triphosphate↗

PubMed1989

Selective potentiation of extracellular Ca2+-dependent contraction by neuropeptide Y in rabbit mesenteric arteries.

1. Neuropeptide Y (NPY) potentiated the contractile responses induced by electrical transmural stimulation, noradrenaline and KCl in the rabbit mesenteric artery. 2. In preparations treated with noradrenaline or KCl in Ca2+ free medium, NPY also potentiated the contractile response induced by resupplementation of Ca2+. 3. 3H-efflux from the arteries preincubated with [3H]-noradrenaline was not affected by NPY. 4. These results suggest that NPY selectively acts on the postsynaptic membrane and potentiates the contractions mediated through receptor-operated and voltage-dependent Ca channels.

Animals↗

PubMed1988

Effects of goniopora toxin on the action potential and membrane currents of guinea-pig single ventricular cells.

The effects of Goniopora toxin (GPT), a polypeptide isolated from a coral, Goniopora spp., on action potential and membrane currents were studied in single ventricular cells of the guinea-pig using the whole-cell clamp technique with a single patch electrode. GPT at a concentration of 10 nmol/l prolonged the duration of the action potential without significant change in the resting membrane potential and action potential amplitudes. This prolongation became more evident at lower stimulus frequencies and persisted after washing with toxin-free solution. Tetrodotoxin (TTX, 1 mumol/l), but not Co2+ (2 mmol/l), abolished the prolonged action potential. Under voltage-clamp conditions, a sustained inward current, not present in the control, followed the transient inward current during depolarizing pulses in the GPT-treated cells. The current-voltage relationship for the sustained inward current was much the same as that for the fast sodium current reported in rat single ventricular cells (Brown et al. 1981). Both the sustained and transient currents were abolished by the shift of holding potential in the direction of depolarization and reappeared after repolarization; the reappearance of the sustained current was much slower than that of the transient current. TTX but not Co2+ abolished both the sustained and transient inward currents. Calcium current and time-independent current were not affected by GPT. Time-dependent outward current induced by large depolarizing pulses was attenuated by GPT.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1988

Single ionic channels induced by palytoxin in guinea-pig ventricular myocytes.

1. Mechanisms of palytoxin-induced ion permeability were examined in isolated single ventricular cells of guinea-pig under whole-cell-attached patch clamp conditions. 2. Palytoxin (1-2 x 10(-11) M, dissolved in Tyrode solution and put in the patch electrode) induced an elementary current flowing through single channels. Direction of the current was inward and the amplitude was 0.65 +/- 0.03 pA (mean +/- s.e. mean) at the resting membrane potential. The amplitude increased linearly with membrane hyperpolarization and decreased with depolarization; the single channel conductance was 9.5 +/- 0.5 pS. 3. Palytoxin-induced single channel current was resistant to tetrodotoxin (5 x 10(-5) M) or cobalt ions (2 x 10(-3) M) and was observed under Ca-free conditions. However, no channel current was induced by palytoxin (10(-11) - 10(-9) M) dissolved in Na+-free, choline-Tyrode solution. 4. Palytoxin also induced single channel currents in Na+-free, NH4+-, Li+- or Cs+-Tyrode solution, and the slope conductances were 16.5 +/- 1.6 pS, 9.2 +/- 0.7 pS and 11.0 +/- 0.7 pS, respectively. 5. These results indicate that palytoxin forms a new type of ionic channel with unique ion selectivity and gating behaviour.

Acrylamides↗

PubMed1988

Tetranitromethane modification of the muscarinic receptors in bovine adrenal medulla.

Muscarinic receptor binding was examined in bovine adrenal medullary microsomes following exposure to tetranitromethane (TNM) that modifies tyrosine and cysteine residues in proteins. The TNM (10-100 microM) treatment of adrenal medullary microsomes caused a concentration-dependent and irreversible reduction in the maximum number of binding sites (Bmax) for l-(3H)quinuclidinyl benzilate (QNB), with a slight increase in the equilibrium dissociation constant (KD). Typically, about a 36% decrease and a 1.3-fold increase in the corresponding values were obtained at 50 microM of TNM. The alteration in the Bmax was partially prevented by atropine but not carbamylcholine, and it was not reversed by subsequent treatment with dithiothreitol, a disulfide reducing agent. The change in the KD was unaffected by these agents. The TNM (50 microM) treatment also caused a slight decrease in the affinity of atropine and pirenzepine (for both the high and low affinity sites), and it caused a slight decrease in the affinity of carbamylcholine at the high affinity site, with a large loss of the low affinity site. Thus, the results indicate that TNM causes a loss of muscarinic binding sites and a decrease in the binding affinity of muscarinic receptors in bovine adrenal medulla, probably through modifications of functional groups such as tyrosine residues.

Adrenal Medulla↗

PubMed1987

Histamine increases the Ca current in guinea-pig ventricular myocytes.

Histamine prolonged the action potential duration and shifted the plateau in an upward direction in guinea-pig ventricular myocytes. Whole cell voltage clamp experiments revealed that histamine increases the amplitude of the inward Ca current with a slight increase in the outward current. Cimetidine but not mepyramine inhibited the effects of histamine. We suggest that histamine increases the Ca current via the mediation of the H2-receptors.

Action Potentials↗

PubMed1987

Muscarinic agonist binding in rat brain following chronic nicotine treatment.

Carbamylcholine binding was determined from competition experiments with [3H] quinuclidinyl benzilate in the rat brain chronically treated with nicotine. The nicotine group exhibited about two-fold lower affinity for the agonist binding toward a high-affinity site (or state) in the cerebral cortex, as compared with the control group. However, no alteration in the agonist binding was observed in the hypothalamus/thalamus and brainstem after chronic nicotine treatment.

Animals↗

PubMed1987

Effect of chronic nicotine treatment against repeated immobilization stress.

Alpha 2 and beta adrenoceptors, and muscarinic cholinoceptors in 2 brain regions (cerebral cortex and hippocampus) were measured in rats which received either tap water or nicotine added to the drinking water (5-8 mg/kg/day) for 4 weeks, and immobilization stress (daily 2 hr) for the last 5 days. The repeated stress induced a reduction in the maximum number of binding sites (Bmax) for (3H)dihydroalprenolol (DHA) in the cerebral cortex of rats with tap water, without affecting (3H)clonidine binding. Nicotine-treatment also caused a decrease in the Bmax of cortical (3H)DHA binding comparable to the case of stress, and increased the (3H)clonidine binding. However, the combination of nicotine- and stress-treatments failed to induce further no changes in the 2 radioligands binding. The binding of (3H)quinuclidinyl benzilate in the cerebral cortex and of the 3 radioligands in the hippocampus was unaltered by nicotine- and/or stress-treatments. These results indicate that long-term administration of nicotine induces down-regulation of cortical beta adrenoceptors and seemingly attenuates the receptor alteration by repeated stress.

Animals↗

PubMed1987

Purinergic and non-purinergic innervation in the cerebral arteries of the dog.

1 Possible involvement of sympathetic purinergic transmission in the neurogenic response of dog cerebral and basilar arteries was examined with the use of alpha, beta-methylene ATP and adrenoceptor, cholinoceptor blocking agents. 2 In the isolated basilar arteries, electrical transmural stimulation produced a transient contraction which was frequently followed by a relaxation. This transient contraction was abolished after desensitization of P2-purinoceptors with alpha, beta-methylene ATP or by treatment with guanethidine. The relaxant response induced by electrical stimulation was also attenuated but was not abolished by such treatments. Prazosin, propranolol and atropine had no significant effect on the responses to electrical stimulation. Yohimbine augmented both the contractile and relaxant responses. 3 In most preparations of the dog middle cerebral arteries, electrical transmural stimulation produced only a relaxation. This relaxation was little affected after treatment with alpha, beta-methylene ATP or guanethidine, and was not inhibited by the other adrenoceptor and cholinoceptor blocking agents. 4 Tetrodotoxin abolished the responses induced by electrical transmural stimulation in both the basilar and middle cerebral arteries. 5 Exogenous ATP (10(-6) and 10(-5)M) produced a transient contraction followed by a relaxation of the basilar arteries and a relaxation of the middle cerebral arteries. Desensitization of P2-purinoceptors abolished the contractile response to ATP without affecting the amplitude of relaxation. 6. In the basilar and middle cerebral arteries preincubated with [3H]-noradrenaline, electrical transmural stimulation evoked an increase in 3H-efflux and this response was markedly inhibited by guanethidine or tetrodotoxin but was not affected by alpha, beta-methylene ATP. Yohimbine increased the evoked 3H-efflux. 7. These findings indicate that cerebral arteries of the dog are innervated by sympathetic purinergic nerves and non-sympathetic nerves which liberate unknown vasodilator substance(s), and that the former nerves are more dominant in the neurogenic response to electrical stimulation of the dog basilar artery than in the middle cerebral artery.

Adenosine Triphosphate↗

PubMed1987

Lack of effects of carbachol on the Na-Ca exchange mechanism in frog atrial muscle treated with goniopora toxin.

Carbachol (CCh) at a concentration of 10(-7) M completely inhibited the twitch contraction of frog atrial muscle. However, when the preparation was treated with goniopora toxin (GPT), a selective inhibitor of Na channel inactivation, and the twitch contraction was augmented through the activation of Na-Ca exchange by this toxin, the reduction in contractile amplitude by CCh was only about 30% even at higher concentrations. The maximum rate of rise of the twitch contraction was not affected by CCh in GPT-treated preparations. The time course of configuration change of the twitch contraction after application of CCh in GPT-treated muscle indicated that the attenuation of amplitude preceded the shortening of duration. The residual contraction under the combined treatments with GPT and CCh was abolished by removal of external Ca++ or addition of TTX. CCh only moderately shortened the action potential which was prolonged by GPT, and further addition of TTX abolished the action potential. From these results, we suggest that CCh does not influence the twitch contraction which is augmented via the activation of the Na-Ca exchange mechanism in frog atrial muscle.

Action Potentials↗

PubMed1987

Effect of several d-morphinans on ascites tumors in mice.

Dextromethorphan and its analogues (DM 16, DM 34, DM 72, DM 75 and DM 96) were examined for their effect on Ehrlich ascites carcinoma or ascites sarcoma-180 in female mice of the ddY strain. The suspension of Ehrlich carcinoma cells or sarcoma-180 cells was prepared from mice at 10 days after i.p. inoculation of the cells, using Hanks' balanced salt solution, and the cell suspension was inoculated i.p. into mice (2 X 10(6) viable cells/mouse). The chemicals dissolved in physiological saline containing 5% HCO-60 were then injected i.p. into the mice once daily for 5 successive days (5-40 mg/kg/day). In addition, mice given the tumor cells were treated with the saline containing 5% HCO-60 alone for 5 days (untreated mice). In groups of mice bearing Ehrlich ascites carcinoma or ascites sarcoma-180, the mean survival time of mice treated with 20-40 mg/kg/day of DM 96 was more than twice that of the corresponding untreated mice. The mean survival time of mice treated with 20 mg/kg/day of DM 96 was also longer than that of mice treated with 40 mg/kg/day of the other chemicals, irrespective of the ascites tumors. Concerning these survival times, the LD50 (i.p.) of DM 96 in mice differed slightly from that of other chemicals (88 mg/kg and 77-106 mg/kg). These results indicate that DM 96 is more active than the other chemicals against the ascites tumors in mice.

Animals↗

PubMed1986

Muscarinic receptor subtypes in bovine adrenal medulla.

Muscarinic receptors in bovine adrenal medullary microsomes were characterized by radioligand binding assay, using l-[3H]quinuclidinyl benzilate (QNB), a muscarinic antagonist. Specific [3H]QNB binding to microsomes was rapid, reversible, saturable and of high affinity. Saturation experiments revealed a single class of binding sites for the radioligand with a maximum number of binding sites and an apparent dissociation constant of 162.6 fmoles/mg protein and 40.3 pM respectively. According to computer-assisted nonlinear regression analysis, however, drug/[3H]QNB competition curves indicated the presence of at least two affinity sites for muscarinic agonists (acetylcholine, carbamylcholine, oxotremorine), with a high (K1) and a low (K2) affinity (e.g. K1 = 664.8 nM and K2 = 36.5 microM for acetylcholine). The two affinity sites for acetylcholine showed only minimal regulation by magnesium and guanosine 5'-triphosphate. Furthermore, the presence of two affinity sites was suggested for the antagonists pirenzepine and gallamine, but not for atropine and pilocarpine. The K1 and K2 values for pirenzepine were 23.7 and 429 nM, respectively, with 54.5% of total sites having a high affinity. These results indicate that at least two distinct subtypes of muscarinic receptors exist in the bovine adrenal medulla and that they are distinguished by their relative binding affinity for muscarinic agonists and antagonists. The receptors are predominantly composed of the affinity state termed M1, as described for the receptors of sympathetic ganglia.

Acetylcholine↗