INTRACELLULAR NA-OUABAIN( ACTIVITY OF DISEASED HUMAN ATRIAL MUSCLES AND ITS MODIFICATIONS BY DIHYDRO)

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