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家兎単離洞結節と房室結節の活動電位に及ぼすアデノシン三リン酸(ATP)の効果を調べた。灌流したATP濃度は,10−8から10−3Mである。
ATPの主作用は,濃度依存性の陰性変時作用で,これは10−4Mテオフィリンで抑制,10−7Mジピリダモールで増強された。またATP 10−6M以上で自発興奮周期延長率は,洞結節より房室結節の方が有意に(P<0.01)大であった。
最大拡張期電位は,ATP濃度上昇により過分極,10−3Mのみ脱分極し,この効果は房室結節のほうが洞結節より大なる傾向にあった。活動電位最大立ち上がり速度は,ATP濃度上昇により増加,10−3Mでのみ減少した。50%再分極時の活動電位幅は,ATP灌流後も有意な変化を示さなかった。
以上より,ATPの主な効果はアデノシンレセプターを介した陰性変時作用で,この効果は房室結節の方が洞結節より大であった。
We showed that higher concentration of adenosine 5'-triphosphate (ATP) was required to prolong the spontaneous cycle length of the sinus node (SN) than that required to prolong the spontaneous cycle length of the atrioventricular node (AVN).
Spontaneously beating preparations of SN and AVN of rabbit (n=8) were superfused with Tyrode solution containing 10-8-10-3M ATP, and action potential was recorded. The negative chronotropic action of ATP was dependent on the concentration. The required concentration of ATP to prolong spontaneous cycle length significantly (p<0. 01) was 10-5M in SN and 10-6M in AVN, respectively. At concentrations higher than 10-6M, the degree of prolongation was greater in AVN than in SN (p<0.01). 10-7M dipyridamole enhanced this effect of ATP, while 10-4M theophylline reduced it.
Action potential duration of 50% repolarization was not changed significantly in either SN or AVN at concentrations up to 10-3M. Maximum diastolic potential (MDP) was hyperpolarized from 10-8M to 10-4M. Hyperpolarization of MDP induced by ATP was greater in AVN than in SN but it was not statistically significant. MDP was depolarized by 10-3M ATP in both SN and AVN. The maximum velocity of depolarization was slightly larger in both SN and AVN as the concentration of ATP was increased in the perfusate. However, it was not statistically significant. 10-3M ATP decreased the maximum velocity of depolarization.
Through these experiments, it is concluded that the negative chronotropic effect of ATP is consider-ed to be developed via the adenosine receptor, and this effect is more potent in AVN than in SN.=
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