Effect of [NO₃] on atrial action potentials and contraction as modified by [Na] and [Ca]

¹ Department of Physiology, Stanford University School of Medicine, Stanford, California

Transmembrane potentials and contractility were measured in driven guinea pig atria according to conventional methods. The effects of nitrate were studied by substituting 40, 60, 80, and 100% of the chlorides with nitrates, and the influence of Ca and Na was determined by varying their ratio in the presence of 40% nitrate. The magnitudes of the resting potential, action potential, and overshoot were reversibly reduced; the rate of depolarization slowed; and the amplitude of contraction decreased as the proportion of nitrate to chloride was increased in the nutrient medium. In general, the initial phase of the repolarization was shortened, but the terminal phase was slowed. The duration of irresponsiveness was prolonged, and the maximum following frequency was reduced by nitrate. Calcium appeared to antagonize the deleterious effects of nitrate on all of the parameters except the resting potential, the negative afterpotential, and the irresponsive period.