Ba2+-sensitive inward rectifier K+ current, I
. Panel A illustrates a series of IK1 elicited on hyperpolarization before (control) and after 1 mM Ba2+ superfusion in a healthy myocyte. Similar traces obtained from a myopathic myocyte are shown in panel B. Horizontal arrows near left margin indicate zero current. The difference current densities (Ba2+-sensitive K+ current, IK1) (mean ± S.E.M.) in 14 healthy myocytes and 12 myopathic myocytes are summarized in the current-voltage relations shown in panel C.