Rabbit atrial myocardium in hypoxic conditions: rate dependent variation of action potential

The dependence of the repolarization phase of the action potential in the atrial myocardium on the pacing pattern was studied in normoxic and hypoxic conditions. Intracellular action potentials were recorded by means of the conventional microelectrode technique from isolated left atrial trabeculae of the rabbit. By varying the pacing pattern and the oxygen supply changes of the configuration of action potential and of the membrane current as well as a conductance measure gK were obtained. In all pacing patterns the duration of action potentials is shortened, and the net outward current is enhanced by hypoxia. In steady state and for premature action potentials, gK is enlarged by hypoxia, but in action potentials after a pacing pause it is diminished more in hypoxic than in normoxic conditions. The findings suggest inhibition of an inward current in hypoxia as well as a dependence of a potassium background conductance on the inner Ca-concentration in normoxic and hypoxic conditions.