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| Abstract |
Although the antiarrhythmic action of nicorandil is drawing an increasing attention, dromotropic effect of this agent is unclear. Therefore, this was investigated by microelectrode technique to the su...perfused guinea pig papillary muscle to record the action potential and extracellular potential during conduction. The correlation of myocardial internal longitudinal resistance (r1) assumed to reflect the global gap junctional resistance, maximum rate of rise of the action potential upstroke (Vmax), and conduction velocity was examined under the alterations of external potassium concentrations ([K+]e ; ranging from 3.0 to 12.0 mM) in the presence or absence of 100μM nicorandil. In the minimum [K+] e, nicorandil caused significant (p < 0.05) hyperpolarization and reduction in Vmax. Negative dromotropic action of nicorandil was slight but significant (p < 0.05) in low (3.0 mM) [K+] e but was not evident in physiologic (5.4 mM) or elevated (9.0 to 12.0 mM) [K+] e. In conclusion, nicorandil exerts negative dromotropic action as [K+] e decreased, which was accounted for by the cable analysis and may contribute to the prevention of low [K+]e-induced arrhythmia.
ニコランジルの抗不整脈作用が近年注目されているが,その変伝導作用は明らかでない.今回これを検討するためにモルモット乳頭筋の表面潅流標本に微小電極法を用いて細胞内活動電位,細胞外電位を同時記録した.また胞内抵抗,活動電位最大立ち上がり速度,伝導速度の関係を外液K+濃度を変化させて(3.0-12.OmM),ニコランジル(100μM)の有無で検討した.ニコランジルを投与すると低K膿度(3.OmM)下で有意な(p<0.05)膜の過分極と活動電位最大立ち上がり速度の減少,さらに興奮伝導速度の減少を認めたが,これらの変化は正常(5.4mM)ないし高K+濃度(9.0-12.OmM)下ではみられなかった.またニコランジルは細胞間の電気的結合の指標である細胞内抵抗には影響しなかった.さらにニコランジルによる活動電位持続時間の短縮はK+濃度が低下するにつれて顕在化した.今回明らかとなったニコランジルの低K+濃度下での陰性変伝導作用は,この様な状態で発生しやすい不整脈に対して抑制的に作用することが期待される.show more
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