Endurance training alters outward K+ current characteristics in rat cardiocytes

The effect of endurance run training on outward K+ currents with rapidly in activating (I-to) and sustained or slowly inactivating (I-sus) characterist ics was examined in left ventricular (LV) cardiocytes isolated from sedenta ry (Sed) and treadmill-trained (Tr) female Sprague-Dawley rats. Iso lated L V cardiocytes were used in whole cell patch-clamp studies to characterize w hole cell I-to and I-sus. Peak I-to was greatest in cells isolated from the Tr group. When I-to was corrected for cell capacitance to yield a current density, most, but not all, of the Sed vs. Tr differences in I-to magnitude were eliminated. Regardless of how I-to was expressed (e.g., I,, or I-to d ensity), the time required to achieve a peak value was markedly shortened i n the cardiocytes isolated from the Tr group. Training elicited a reduction in I-to, density. Action potential characteristics were determined in Sed and Tr cardiocytes in primary culture. Training did not affect resting memb rane potential, whereas peak membrane potential was reduced and time to pea k membrane potential was prolonged in the Tr group. In addition, time to 50 % repolarization was signiticantly increased in cells from the Tr group. Co llectively, these data indicate that I-to and I-sus characteristics are alt ered by training in isolated LV cardiocytes. These alterations in I-to and I-sus may be responsible, at least in part, for the training-induced altera tions in action potential configuration in cardiocytes in primary culture.