Green Tea Catechins Increase the Force of Contraction in Isolated Guinea Pig Atrial Muscle Preparations by Increasing the Amplitude of Intracellular Ca2+ Concentration

It has been reported that green tea catechins enhance the force of contraction of isolated heart muscle preparations. However, it remains controversial whether or not the increase in force of contraction is related to an increase in the intracellular Ca2+ concentration ([Ca2+]i). In this study, the relationship was investigated using a left atrial muscle preparation isolated from guinea pig heart. In the left atrial muscle preparations without fura-2/AM loading, neither EGC (epigallocatechin) nor EC (epicatechin) influenced the force of contraction, but EGCG (epigallocatechin gallate) and ECG (epicatechin gallate) increased the force of contraction in a dose-dependent manner. The ED50 value of EGCG was significantly higher than that of ECG. In the atrial muscle preparations loaded with fura-2/AM, EGCG and ECG increased the amplitude of [Ca2+]i(peak [Ca2+]i minus diastolic [Ca2+]i) which is associated with the increase in force of contraction. Simple regression analysis between the degree of increase in the force of contraction and the increase in the amplitude of [Ca2+]i revealed a positive correlation in EGCG, ECG and CaCl2. In addition, the slopes of the regression lines of EGCG and ECG were comparable with those of CaCl2. It was suggested that atrial muscle preparations had a higher affinity for ECG than EGCG, and that the increase in the force of contraction by EGCG and ECG was closely related to the increase in the amplitude of [Ca2+]i.