The influence of inorganic ions on the uptake and retention of tritiated noradrenaline by isolated perfused rat hearts.

Abstract

The influence of a variety of modified Krebs media on the cumulative uptake of 3H-noradrenaline (3HNA) by perfused rat hearts was tested, and followed immediately by a determination of the effects of those altered media on the efflux of the tritiated compounds retained in the hearts. The efflux data were analyzed with the aid of a computer-assisted program for curve stripping and compartmental analysis, to indicate the distribution of 3HNA in the hearts. By this program the tritiated material in the heart was divided into four fractions: the nonspecific bound, the neuronal bound, the extraneuronal bound, and the free and loosely bound fractions. The results obtained from these experiments are summarized below. (1) Cocaine and desmethylimipramine reduced binding and passage of 3HNA into all cells, and in their presence the infused 3HNA was largely confined to the extra cellular space without uptake into tissue cells. (2) Reserpine prevented neuronal binding but the extraneuronal, the nonspecific, and the free and loosely bound fractions were also reduced, suggesting that reserpine may have some cocaine-like action. (3) Low calcium conditions increased uptake into the extraneuronal and the free and loosely bound fractions but reduced nonspecific binding. (4) EDTA reduced neuronal and extraneuronal binding but increased nonspecific binding and the amount in the free and loosely bound fraction. The effects of EDTA were similar to those of reserpine but had no cocaine-like action. (5) A high sodium concentration in the perfusion fluid increased binding in all fractions but under sodium-free conditions the neuronal and extraneuronal bound fractions were decreased while the nonspecific bound and the free and loosely bound fractions were increased. Neuronal binding required sodium but was not proportional to the concentration of sodium in the extracellular fluid. (6) Anions in the perfusion fluid influenced the uptake and distribution of 3HNA. Na2SO4 substituted for NaCl increased neuronal binding. NO3 and sodium cyanide substitution decreased neuronal binding but increased extraneuronal binding and the free and loosely bound fraction. The observations are consistent with the hypothesis that free Ca ions may inhibit transport and binding systems for noradrenaline in both nerve and extraneuronal tissues, probably largely muscle, and that alterations in the ionic environment which influence the availability of free Ca ions may influence the distribution of noradrenaline in perfused rat hearts.