“…When operating in its forward mode (Ca 2 þ efflux), the exchanger contributes to diastolic relaxation and counterbalances Ca 2 þ entry via Ca 2 þ channels (Carmeliet, 1992;Bers et al, 2003); when operating in its reverse mode, it promotes a Ca 2 þ influx that contributes to Ca 2 þ loading of the sarcoplasmic reticulum and/or Ca 2 þ release from the organelle (Crespo et al, 1990;Leblanc & Hume, 1990;Lipp & Niggli, 1994;Litwin et al, 1998;Meme et al, 2001;Bers et al, 2003). In either mode, I NCX affects the configuration of the action potential (Mitchell et al, 1984;Noble et al, 1991;Janvier & Boyett, 1996;Wei et al, 2003).…”