Intracellular Na+ activity of "diseased" human atrial muscles and its modifications by dihydro-ouabain

In quiescent human atrial muscles obtained from patients with various cardiac diseases, the intracellular Na+ activity (aNai) and the resting membrane potential (Vm) were recorded simultaneously, using double-barreled Na(+)-selective microelectrodes. The Vm averaged -44.1 +/- 5.0 mV and the aNai, 6.9 +/- 1.7 mM under normal Tyrode's solution containing 5.4 mM [K]oi,The aiNa value was within the range of aNai reported in various cardiac tissues from intact animals. Dihydro-ouabain (10(-5) M) significantly increased the aNai and depolarized the Vm. The results suggest that even in these depolarized atrial muscles the aNai remains within physiologic levels and that the Na-K pump may not be impaired. This is the first report to measure the aNai in human atrial muscles.