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Như gần đây đã xem xét lại, sự thay đổi đó biến với mức độ phì đại, giai đoạn mất bù và kích thích kinh tế hàng đầu để tu sửa (Schillinger et al 2003;. Sipido et al 2002;. Verdonck et al 2003b). Điều này cảnh báo chống lại các kịch bản khái quát về trao đổi Na / Ca phì và suy tim. | 176 K. R. Sipido et al. will affect the contribution of the Na Ca exchanger to electrical activity and potential arrhythmogenesis. The most immediately relevant changes are altered expression of the Na Ca exchanger and modulation of exchanger activity due to altered Ca2 i and Na i. As recently reviewed such changes are variable with the degree of hypertrophy stage of decompensation and the stimulus leading to remodelling Schillinger et al. 2003 Sipido et al. 2002 Verdonck et al. 2003b . This cautions against generalizing scenarios on the Na Ca exchanger in hypertrophy and heart failure. Nevertheless from data on some of the best-studied examples of remodelling some important aspects can be highlighted. 4.2.1 Increased Ca2 Removal via NCX in End-Stage Heart Failure In myocytes from human hearts obtained at the time of transplantation Ca2 i transients are prolonged and Ca2 uptake into the SR is reduced Beuckelmann et al. 1992 Hasenfuss and Pieske 2002 Piacentino III et al. 2003 . This promotes removal of Ca2 via the Na Ca exchanger. Although the amount of charge extruded by the exchanger in steady state is determined by the amount of Ca2 entry not by the expression activity levels of NCX Bridge et al. 1990 Negretti et al. 1995 the latter will determine the kinetics of the current and time course of Ca2 removal. Therefore an increased inward current at the end of the action potential can be part of the prolongation of the action potential typically seen in human heart failure. Increased Ca2 removal through NCX has also been observed in some well-characterized animal models of heart failure. In the dog with tachycardia-induced heart failure the increased Ca2 removal is the result of reduced SR Ca2 uptake and increased activity and expression of the exchanger Hobai and O Rourke 2000 O Rourke et al. 1999 . Modelling of the electrical activity in this dog model however did not clearly indicate that this will contribute to action potential prolongation Winslow et al. 1999
