| Co-Investigator(Kenkyū-buntansha) |
KOJIMA Hiroshi Kyoto University Faculty of Medicine, 医学部, 研究員 (50281671)
HARADA Yoshio Kyoto University Faculty of Medicine, 医学部, 助手 (30181027)
YAWO Hiromu Kyoto University Faculty of Medicine, 医学部, 助手 (00144353)
TAKAHASHI Tomoyuki Kyoto University Faculty of Medicine, 医学部, 講師 (40092415)
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| Budget Amount *help |
¥9,500,000 (Direct Cost: ¥9,500,000)
Fiscal Year 1986: ¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 1985: ¥6,500,000 (Direct Cost: ¥6,500,000)
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| Research Abstract |
While peptide-receptive cells are widely distributed in both the central and peripheral nervous systems, these cells are too small to analyze detailed ionic mechanisms associated with activation of the receptors. The present study has been addressed to the analysis of ionic mechanisms underlying activation of the peptide receptors expressed in Xenopus oocytes which have a diameter of about 1 mm. For this purpose, mRNA isolated from the rat brain or the bovine stomach was injected into oocytes, and the response of the injected oocytes to a variety of peptides was recorded under voltage clamp following incubation for a few days. While the receptors to five different peptides could be expressed by this technique, the study was focused on the substance P receptor. Substance P is a member of the tachykinin family. At present, in addition to substance P, two other tachykinins, substance K and neuromedin K, are known to exist in the mammalian nervous system. In accord with the presence of mul
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tiple tachykinins, the existence of three subtypes of tachykinin receptors has been suggested. The three subtypes of tachykinin receptors could be distinguished by potency ranking of different tachykinin agonists. On this basis, the tachykinin receptor induced by rat brain mRNA was found to correspond to the SP-P tachykinin receptor, whereas that directed by bovine stomach mRNA corresponded to the SP-K tachykinin receptor. Thus, two different types of tachykinin receptors could be induced in the same expression system, depending upon the source of exogenous mRNA injected. This indicates that the two receptors are made of different molecules. Therefore, the difference in nature between the two receptors cannot be attributed to the possible posttranslational modification occurring at their destination tissue alone. On the other hand, the ionic mechanisms responsible for activation of the two receptors are both based on an increase in the <Cl^-> conductance. This suggests that activation of the two receptors uses the same intracellular second messenger, which in turn, activates <Cl^-> ionic channels in the oocyte membrane. The nature of the second messenger may be different between oocytes and mammalian neurons. Therefore, the ionic mechanisms analyzed in oocytes cannot be generalized to activation of tachykinin receptors present in other species. Less
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