open access

https://doi.org/10.11501/3137173

https://hdl.handle.net/2115/51476

Responses and pharmacological classification of purinoceptors : Studies in guinea-pig adrenal chromaffin cells and rat gastric circular smooth muscle

日本語

1998-03-25

Hokkaido University

86p.

The effects of extracellular ATP on voltage-dependent Ca2+ channels were examined using the whole-cell voltage-clamp technique in guinea-pig isolated adrenal chromaffin cells, and those of ATP and its related compounds on contractile and relaxant responses were studied to characterize the purinoceptor subtypes in rat gastric circular smooth muscle. 1. In guinea-pig isolated adrenal chromaffin cells, ATP (500μM) evoked an inward current (IATP) and a rise of intracellular Ca2+ concentration under the whole-cell voltage-clamped (-70mV) condition. 2. When the intracellular solution contained 0.1 or 1 mM EGTA, the inhibitory effect of ATP (500μM) on ICa tended to depend on the peak amplitude of IATP- However, this inhibitory effect was also seen even in the cells that IATP was not evoked. When the concentration of EGTA was increased to 10 mM, the inhibitory effect became independent of the amplitude of IATP. 3. In the presence of 10 mM Ba2+, ATP (100μM) reduced Ba2＋ currents (IBa) in a manner similar to ICa. This reduction was decreased by dialysis of cells with the internal solution containing GDPβS (1mM) or GTPγS (100μM). A depolarizing prepulse to +100 mV partly relieved ATP-induced reduction of IBa. 4. ADP (100μM), AMP (100μM) and adenosine (100μM) also reduced IBa and the effect of adenosine was the most potent. Adenosine and AMP (0.5 and 1 mM) inhibited adrenaline secretion induced by nicotine (50μM). 5. In rat gastric circular smooth muscle tissues contracted by acetylcholine (1μM), ATP, 2-methylthio ATP (2MeSATP), α,β-methylene ATP (α,β-meATP) and adenosine each caused relaxation in a dose-dependent manner. α,β-MeATP was the most potent and UTP was a weak agonist inducing relaxation. 6. 8-Phenyltheophylline (3μM) inhibited the relaxant response to adenosine but not that to ATP or α,β-meATP. Reactive blue 2 (RB2: 1 and 3μM) and suramin (10-100μM) inhibited the relaxant responses to ATP and α,β-meATP. PPADS (3-30μM) and DIDS (10-100μM) inhibited the relaxation caused by α,β-meATP but not by ATP. 7. Both ATP-and α,β-meATP-induced relaxations were inhibited by apamin (0.3μM). 8. In tissues at resting tone, ATP and its related compounds caused contractions with the rank order of potency; 2MeSATP＞＞ ATP ≥ UDP = UTP ≥ ATPγS ＞＞ α,β-meATP ＞ adenosine = 0. 9. RB2 (1 and 3M) and suramin (10-100μM) inhibited both ATP-and UTP-induced contractions. On the other hand, PPADS (30μM) inhibited the contraction caused by UTP but not by ATP. 10. Desensitization with 2MeSATP (0.1μM) or ATPγS (100μM) decreased contraction caused by ATP but not by UTP. Desensitization with UTP 100μM) slightly decreased ATP-induced contraction. UTP-induced contraction was not inhibited by desensitizaiton with 2MeSATP (0.1μM), ATPγS (100μM) or ATP (100μM). 11. ATP (100μM)- and UTP (100μM)-induced contractions were inhibited by the removal of extracellular Ca2+ or the application of nifedipine (1μM). In guinea-pig adrenal chromaffin cells, these results suggest that Ca2+ entry through ATP-activated non-selective cation channels results in the inactivation of voltagedependent Ca2+ channels, in addition, that ATP modulates Ca2+ channels via the pathway related to GTP-binding protein. Since adenosine is the most potent agonist in inhibiting Ca2+ channels, P1 and P2 receptors seem to coexist in guinea-pig adrenal chromaffin cells. On the other hand, in rat gastric circular muscle, these results suggest that there are two purinoceptors mediating relaxation, PPADS and DIDS-resistant P2Y receptors, and PPADS and DIDS-sensiti ve P2 receptors activated by α,β-methylene ATP, and that apamin-sensitive K+ channels are involved in the relaxant responses to these adenine nucleotide. In addition, it was suggested that ATP and UTP caused contractions via P2Y receptors and pyrimidinoceptors, respectively, and that these contractions were caused by the Ca2+ entry through voltage-dependent Ca2+ channels. The pyrimidinoceptors were inhibited by P2 receptor antagonists, RB2, suramin and PPADS in rat stomach. In summary, there are some purino- and pyrimidinooeptors in both chromaffin cells and smooth muscle cells. ATP and its related compounds may play a role as a transmitter in these tissues.

1998-03-25

甲第4457号

博士(獣医学)

博士論文

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