Figure 7. Na/K pump and Na/Ca exchange currents in myocytes that overexpress NCX1 Na/Ca exchangers by more than five-fold.
The cytoplasmic (pipette) solution is designed to highly buffer free Ca and protons. The magnitudes of exchange currents after 15 s are much greater than the 15 s pump currents. Thus, Na/K pumps and Na/Ca exchangers cannot be sharing a restricted subsarcolemmal space. Top panel. Complete current record in which Na/K pump currents and Na/Ca exchange curerrents were activated alternately. Bottom panel. Expanded view of the current record to accurately depict the Na/K pump current. Pump currents decay completely before activation of Na/Ca exchange. In response to Na/Ca exchange currents, peak pump currents double and a maintained current develops. These changes reverse completely over 3 min after the last Ca elevation.