Previous-beat contraction history is not influenced by mechanosensitive ion channel blockade

OBJECTIVES: Prior studies have shown that the performance of the left ventricle on any one beat is influenced by the mechanical events of the previous beat, a phenomenon called "previous-beat contraction history". This previous-beat contraction history, which appears to be an interplay between the mechanical events of one contraction and the activation state of the next contraction, could depend, at least in part, on mechanosensitive ion channels. The purpose of this study, therefore, was to test the hypothesis that mechanosensitive ion channels contribute to previous-beat contraction history: If previous-beat contraction history depends on mechanosensitive ion channels, the magnitude of its effect should be decreased by blocking mechanosensitive ion channels. METHODS: We performed experiments in buffer-perfused isolated rabbit hearts in which left ventricular pressure and volume were controlled with a servo-motor system. We evaluated the pulse interval-dependent expression of previous-beat contraction history under control conditions (no drug) and in the presence of 100 and 500 microM streptomycin, a blocker of mechanosensitive ion channels. RESULTS: Under control conditions, previous-beat contraction history nor its dependence on pulse interval was influenced significantly by either concentration of streptomycin. CONCLUSION: Mechanosensitive ion channels do not play a role in the expression of previous-beat contraction history in the left ventricle of the isolated rabbit heart.