A Reciprocal Effect of 532/808 nm Low-Power Laser Irradiation on The Frog Cardiac Automatism: A Possibility of Ih (Hyperpolarization-Activated Cation Current) Channel Modulation as Its Underlying Mechanism

Abstract

Based on our hypothesis that low-power laser irradiation (LLI) influences a hyperpolarization-activated cation current (Ih), we examined the effects of LLI on cardiac automatism of the frog heart because the Ih was firstly identified in the rabbit heart as a pacemaker channel. ECG was directly recorded. In control group, the heart rate gradually decreased and stopped with an average survival time of 14.9 ± 3.4 h (mean ± SD). 532 nm LLI induced a transient tachycardia and resulted in a prolongation of survival time, whereas 808 nm LLI did bradycardia and a reduction of survival time. An Ih blocker, ZD7288 application induced bradycardia as well as reduction of survival time. The simultaneous application of LLI and ZD7288 put out the LLI effect but remained the blocker effect. It is concluded that LLI effects on cardiac automatism are induced by a certain process of activation or inactivation in pace-making channels.