Differential effects of a green tea derived polyphenol (−)‐epigallocatechin‐3‐gallate on the muscle‐specific decrease in calcium response to acidosis

Abstract

(−)‐Epigallocatechin‐3‐gallate (EGCg), a green tea derived polyphenol, has received much attention as a protective agent against cardiovascular diseases. In this study, we determined the effects of EGCg on changes in pH sensitivity of myofilament response to Ca2+ in myofibrils prepared from porcine ventricular myocardium and chicken pectoral muscle. In comparison with skeletal muscle, lowering pH from 7.0 to 6.5 and/or 6.0 EGCg has significantly blunted the acidic effect on the reduction of Ca2+ sensitivity for myofibrillar ATPase activity in cardiac muscle. Studies with recombinant mouse cardiac (cTnC) and chicken fast skeletal troponin C (sTnC) by circular dichroism (CD), intrinsic and extrinsic fluorescence spectroscopy showed that EGCg specifically binds to cTnC with a dissociation constant ~ 3–4 μM, but no effect on sTnC. Presumably binding to the cTnC C‐lobe, EGCg acted to alter the Ca2+‐binding to cTnC and compromised the interference of proton effect on the Ca2+ binding at acidic pH. To demonstrate the isoform‐specific effects on the action of EGCg, the pH‐sensitivity of Ca2+ response was examined in cardiac myofibrils replaced with either sTnC or cTnC and skeletal myofibrils exchanged with whole cardiac Tn complex (cTn). The data obtained suggested that EGCg interactions with the cardiac isoform specific TnC or Tn complex could alter the pH effect on myofilament Ca2+ sensitivity in striated muscle.