Na+-Ca2+ exchange current (NCX) in healthy (panel A) and myopathic LA-PV myocytes (panel B). The clamp protocol is shown between panels A and B. The holding potential was -40 mV. Horizontal arrow at left margin indicates zero current. For inward NCX currents the myocyte was hyperpolarized Vh -40 to -100 mV in 20 mV increments. For outward NCX currents, the myocyte was depolarized from -40 to +100 mV in 20 mV increments. Mean current-voltage relationships of NCX in 6 healthy and 5 myopathic myocytes (from 3 hamsters in each group) are summarized in panel C.