モルモット洞房結節細胞におけるプロスタグランジンの自動能促進作用

抄録

It has been reported that thromboxane A₂ (TXA₂) and prostaglandin F₂ (PGF_2α) mediates inflammatory tachycardia by directly facilitating the automaticity of cardiac sinoatrial node preparations (Takayama et al, 2005). In this study, the action potential and membrane currents were recorded in isolated guinea-pig sinoatrial node cells and the ionic mechanisms underlying the positive chronotropic action of PGF_2α and TXA₂ were investigated by the patch clamp method. Both PGF_2α and TXA₂ increased the spontaneous firing frequency of isolated sinoatrial node cells, and this increase was partially blocked by 50 μM Ni²⁺. Under the voltage clamp condition, I-BOP, a selective agonist for TP receptor, increased the amplitude of low voltage-activated Ca²⁺ current with little affecting the high-threshold Ca²⁺ current, the delayed rectifier K⁺ current and the hyperpolarization-activated cation current. In the single channel recording, I-BOP increased the open probability of Ca²⁺ channels, which had tiny (-8pS) conductance and displayed rapid inactivation. The results indicate the functional role of T-type Ca²⁺ channel in the positive chronotropic action of PGF_2α and TXA₂. [J Physiol Sci. 2008;58 Suppl:S58]