心筋細胞内カルシウムトランジュン一に対するハイブリッドロジスティック関数を用いたカーブフィット

摘要

As the left ventricular (LV) pressure curve and myocardial tension curve in heart are composed of contraction and relaxation processes, we have found that hybrid logistic (HL) function calculated as the difference between two logistic functions curve-fits better the iso-volumic LV pressure curve and the isometric twitch tension curve than the conventional polynomial exponential and sinusoidal functions. Increase and decrease in intracellular Ca~(2+) concentration regulate myocardial contraction and relaxation. Recently, we reported that intracellular Ca~(2+) transient (CaT) curves measured using the calcium-sensitive bioluminescent protein, aequorin, were better curve-fitted by HL function compared to the polynomial exponential function in the isolated rabbit RV and mouse LV papillary muscles. We speculate that the first logistic component curve of HL fit represents the concentration of the Ca~(2+) inflow into the cytoplasmic space, the concentration of Ca~(2+) released from sarcoplasmic reticulum (SR), the concentration of Ca~(2+) binding to troponin C (TnC), and the attached number of cross-bridge (CB) and their time courses, and that the second logistic component curve of HL fit represents the concentration of Ca~(2+) sequestered into SR, the concentration of Ca~(2+) removal from the cytoplasmic space, the concentration of Ca~(2+) released from TnC, and the detached number of CB and their time courses. This HL approach for CaT curve may provide a more useful model for investigating Ca~(2+) handling, Ca~(2+) -TnC interaction, and CB cycling.