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Biomedical subjects

K Takeyasu

Publications and source records attributed to K Takeyasu.

At least 91 records · Page 5Linked to original sources
PubMed1982

Activation and inactivation kinetics of Torpedo californica acetylcholine receptor in reconstituted membranes.

By use of a quench-flow technique to measure tracer ion flux rates in a physiologically significant time domain, the kinetics of activation and inactivation of purified reconstituted acetylcholine receptor (AChR) were investigated. After solubilization in sodium cholate, purification by affinity chromatography, and reconstitution into soybean lipids, the AChR from Torpedo californica displayed a characteristically fast rate of ion influx measured with 86Rb+. At 4 degrees C 1 mM carbamoylcholine (Carb) stimulated a fast (t1/2 = 7 ms) first-order filling of vesicle internal volume that presented a 10(4)-fold stimulation of ion flux rate by Carb. The concentration dependence of activation was sigmoidal with a half-maximal value at 3 X 10(-4) M Carb. In the presence of Carb, the purified AChR also underwent a two-step inactivation (desensitization) process. Inactivation was measured by preincubating AChR with Carb for various times (milliseconds to minutes) and then measuring the 86Rb+ influx rate. The two inactivation processes were each characterized by a distinct maximum rate (5.3 and 0.10 s-1) and by a different dependence on Carb concentration. The slow phase of inactivation gave a half-maximal rate at 2.5 X 10(-4) M Carb, and the fast inactivation was half-maximal at 1.3 X 10(-3) M Carb. The concentration dependence curves for both inactivation processes were approximately hyperbolic. The results are discussed in terms of models that describe the relationship between ligand binding and the processes of channel activation and desensitization.

Acetylcholine↗
PubMed1982

Molecular mechanism of the effects of guanine nucleotide and sulfhydryl reagent on muscarinic receptors in smooth muscles studied by radiation inactivation.

The molecular sizes of the units concerned in 3-quinuclidinyl benzilate (QNB) binding and in the effects of guanine nucleotide and sulfhydryl reagent on the inhibition of QNB binding by carbachol in smooth muscle of guinea pig ileum were determined to be 76,000, 179,000 and 107,000, respectively by the radiation inactivation method. One or more subunits (GTP subunit) other than the receptor subunit in a muscarinic receptor appeared to be involved in the effect of guanine nucleotide. When guanine nucleotide was present, the receptor subunit seemed to be dissociated from the GTP subunit.

Animals↗
PubMed1982

Effects of trypsin-treatment on agonist binding affinity to the muscarinic acetylcholine receptor.

Trypsin-treatment of the microsome fraction of the ileum and the synaptic membrane fraction of the cerebral cortex of guinea-pig caused selective reduction in the apparent affinity of an agonist (carbachol), but not an antagonist (atropine), to muscarinic acetylcholine receptors (mAChR), measured as inhibition of binding of 3H-quinuclidinyl benzilate (3H-QNB). This effect was similar to that of Gpp(NH)p. The effects of trypsin and Gpp(NH)p were not additive. On the other hand, treatment of these fractions with 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) increased the apparent affinity of agonist, but not antagonist. The effect of DTNB predominated over those of trypsin and Gpp(NH)p, when the fractions were treated with two reagents simultaneously.

Animals↗
PubMed1982

Desensitization of the alpha adrenergic receptor system in guinea pig vas deferens.

Desensitization induced by alpha adrenergic (alpha-Ad) stimulation was investigated in organ cultured vas deferens of guinea pig. Brief exposure (1-2 min) of the muscle to noradrenaline (NA) caused short-term desensitization to both NA and acetylcholine (ACh), but not to high K+. After removing the agonist this desensitization completely disappeared within 15 min. Prolonged exposure to NA (i.e., cultured with NA for 3-24 hr) elicited long-term desensitization to NA, ACh and K+ (50 mM), but it did not change the maximal contraction by high K+ (154 mM). After removing NA from the culture medium the response to the agonist was restored to normal within 24 hr, but not within 15 min. The number and affinity of alpha-Ad and muscarinic ACh receptors, which were measured by the binding of 3H-WB4101 and 3H-QNB, respectively, were not changed in the muscle during these treatments. Moreover, long-term desensitization, but not short-term desensitization, was depressed by the concomitant presence of cycloheximide. The possible mechanisms of desensitization were discussed in comparison with those of various receptor systems.

Acetylcholine↗
PubMed1982

Mechanism of agonist-induced degradation of muscarinic cholinergic receptor in cultured vas deferens of guinea-pig.

The mechanism of agonist-induced degradation of muscarinic cholinergic receptors (mAChRs) was examined by means of [3H]QNB binding by organ-cultured guinea-pig vas deferens. Long-term exposure to ACh decreased the surface mAChR. This so-called 'down regulation' of mAChR was significantly inhibited by anti-endocytotic drugs. Anti-microtubular agents also strongly inhibited the decrease of mAChR remaining on the cell surface. Ammonium chloride and protease inhibitors, which are known to inhibit lysosomal enzymes, had little effect on the decrease and no increase in intracellular mAChR could be detected under these conditions. Chloroquine blocked the decrease in mAChR remaining on the cell surface. Based on these findings, the involvement of clustering and endocytosis in mAChR degradation were considered as possibilities. Furthermore, contraction of the smooth muscle to ACh in long-term desensitization was also examined in relation to the number and nature of the receptors. When the muscles were cultured with ACh and chloroquine or vinblastine, there were indications that the surface mAChR and the contractile system were uncoupled.

Acetylcholine↗
PubMed1982

Developmental changes in alpha-adrenergic and muscarinic receptor-mediated contractions of rat vas deferens.

Studies were made on developmental changes in phasic contractions of isolated rat vas deferens in response to norepinephrine (NE) and acetylcholine (ACh), which are mediated by alpha-adrenergic and muscarinic cholinergic receptors (alpha-R and m-R). The ED50 values of both contractions were almost constant during development, but the maximum responses to NE and ACh per wet weight and the relative contractions by NE and ACh to that by 100 mM K+ decreased greatly between 3 and 8 weeks after birth. However, the alpha- and m-receptors, assayed by measuring binding of [3H]-WB4101 and [3H]-quinuclidinyl benzylate (QNB), increased quantitatively per g wet weight and per mg protein between 2 and 8 weeks after birth, but did not change qualitatively. Thus, a discrepancy between the increases of alpha- and m-receptors and decreases of the maximum responses to NE and ACh was found, and possible mechanisms for this are discussed.

Acetylcholine↗
PubMed1982

Regulation of the alpha-adrenergic system in rat vas deferens.

Regulation of the supersensitivity and subsensitivity of the alpha adrenergic (alpha-Ad) system of rat vas deferens cultured under various experimental conditions was investigated. Muscles cultured for 3 days in normal medium (Eagle's MEM) exhibited marked increase in maximal contraction to noradrenaline (NA) and high K+ (154 mM), while muscles cultured with NA (100 microM) were subsensitive to the stimulants. Studies on the binding of 3H-WB4101, an alpha-Ad antagonist, to the homogenates of normal, supersensitive and subsensitive muscles revealed that the changes in NA-sensitivity were not accompanied by changes in the number or affinity of alpha-Ad receptors in the muscles. The effect of NA in decreasing NA-sensitivity was depressed by an inhibitor of protein synthesis, puromycin or cycloheximide. These results suggest that NA may be important in regulation of the contraction, at least in part through protein synthesis, without affecting the number or affinity of alpha-Ad receptors.

Adrenergic alpha-Antagonists↗
PubMed1981

Receptor-activated and energy-dependent decrease of muscarinic cholinergic receptors in guinea-pig vas deferens.

Organ cultures of guinea-pig vasa deferentia were used for studying both the decrease in muscarinic cholinergic receptor (mAChR) concentration induced by muscarinic agonists and the simultaneous decrease in contraction to ACh. After a lag period the decrease followed first-order kinetics and was completely blocked by atropine. The decrease was dependent not only on the extent of occupation of mAChR by ACh, but was also related to the efficacy of agonists as deduced from the contractions. Moreover the amount of mAChR was not affected by other contractile agents, norepinephrine and high K+ even under conditions in which mAChR was occupied by atropine or pilocarpine. These findings indicate that the decrease in the amount of mAChR mediated by muscarinic receptors in vas deferens was due to the extent of both receptor occupation and receptor activation by agonists. Furthermore it was shown that the decrease involved energy- and temperature-dependent processes and that cyclic nucleotides did not regulate the quantitative level of mAChR.

Animals↗
PubMed1981

Role of alpha-adrenergic receptors in denervation supersensitivity of rat vas deferens.

Contractile responses of rat vas deferens were studied with particular attention directed to the role of receptors and neuronal control. Marked contraction of the vas deferens was observed with alpha-adrenergic agonists, depending on their concentrations. This tissue had a low sensitivity to ACh. Four days after denervation, this tissue showed a supersensitivity to alpha-adrenergic agonists and a high K+ concentration, but not to ACh. The increase in sensitivity to alpha-agonists resulted in an enhancement of the maximal response and a shift of the concentration response curve to lower concentrations of these reagents. Alterations were seen in the alpha-adrenergic receptors in the rat vas deferens, assayed by measuring the binding of [3H]WB4101. The maximal binding sites decreased significantly to 86 from 142 fmoles per mg protein. The affinity of the receptors for alpha-agonist, determined by measuring the ability of agonists to displace bound [3H] WB4101, increased significantly, while the affinity to alpha-antagonists remained unchanged. Studies on [3H]QNB binding indicated no significant change in muscarinic ACh receptors after denervation. Thus, supersensitivity of the alpha-adrenergic mechanism mediated by a specific change in affinity of alpha-receptors occurs after denervation of rat vas deferens. These changes in sensitivity and in receptors are discussed in relation to the characteristics and roles of alpha-receptors in the rat vas deferens.

Acetylcholine↗
PubMed1981

[The comparison of blood levels between peripheral vein and tooth extraction wound after the oral administration of antibiotics (author's transl)].

The oral administration of 300 mg of clindamycin was undertaken on 23 patients, of 500 mg of cefadroxil on 11 patients and of 250 mg of talampicillin on 12 patients, and then tooth extraction was performed under local anesthesia. Blood samples were taken from the extraction wound and the peripheral vein at the same time and assayed by the bioassay method. The blood levels of clindamycin and cefadroxil indicated a similar pattern between the extraction wound and the peripheral vein, but the blood level of talampicillin reached peek level rapider than clindamycin and cefadroxil. The blood levels of the extraction wound were 60 - 80% as compared with the venous blood levels with each antimicrobial agent.

Administration, Oral↗
PubMed1980

Increase in response and number of alpha-adrenoceptors of rat vas deferens on brief pretreatment with an alpha-agonist.

The contractile response of rat vas deferens to epinephrine (E) was enhanced by preincubation with E. After pretreatment with E, there was no significant change in the ED50 of E but there was a significant increase in the maximum response (39%). There was no change in the cholinergic response after the pretreatment. alpha-Adrenoceptors in control and E-treated tissues were assessed by measuring [3H]WB-4101 binding. Treatment with E resulted in a 27% increase in the number of alpha-adrenoceptors, but no change in muscarinic acetylcholine receptors measured with [3H]quinuclidinyl benzilate. These results are discussed in relation to the response of alpha-adrenoceptors to the agonist.

Adrenergic alpha-Agonists↗
PubMed1980

Specific changes in the cholinergic system in guinea-pig vas deferens after denervation.

A small rapid phase (1st phase) was distinguished from a concomitant phase (2nd phase) in contraction of guinea-pig vas deferens. The vas deferens 4 days after denervtion exhibited supersensitivity to stimulants. The supersensitivity in the 2nd phase of contraction was nonspecific, but that in the 1st phase was specific to muscarinic cholinergic agonists. The increase in sensitivity resulted in a shift of the dose-response curve to lower concentrations without significant change in the maximal response. Muscarinic cholinergic receptors in the vas deferens, determined by measuring binding of [3H]quinuclidinyl benzilate, changed after denervation. The maximal binding sites increased from 115 to 165 fmol/mg of protein with no significant change in the dissociation constant. The affinity of the receptor for agonist also did not change significantly. Studies on [3H]WB4101 binding indicated no significant change in alpha adrenergic receptors after denervation. Thus, specific supersensitivity of the cholinergic mechanism mediated by muscarinic acetylcholine receptors occurred after denervation of guinea-pig vas deferens. This increased sensitivity is discussed in relation to the amount of receptor.

Acetylcholine↗