THE POSITIVE INOTROPIC ACTIVITY OF TETRAETHYLAMMONIUM IONS AND THEIR EFFECT ON RADIOCALCIUM MOVEMENT

¹ Baker Medical Research Institute, Melbourne, Australia

The effect of tetraethylammonium ions (TEA⁺) on the contractile activity, shape and duration of the action potential, and the uptake and release of Ca⁴⁵ by toad ventricular muscle has been investigated.

Tetraethylammonium ions (0.1 to 5 mM) increased the contractile amplitude and prolonged the duration of the action potential. Higher concentrations of tetraethylammonium ions caused the development of contracture.

Ventricles which, after 15 minutes perfusion with calcium-free Tyrode solution failed to contract when electrically stimulated, regained their ability to contract in response to electrical stimulation when perfusion was continued with calcium-free Tyrode solution containing tetraethylammonium chloride in excess of 1 mM. After 4 hours perfusion in the absence of extracellular calcium ions, tetraethylammonium ions failed to restore the ability of other electrically stimulated ventricles to contract.

Two mM tetraethylammonium ions increased the uptake and release of Ca⁴⁵ from stimulated and quiescent (nonstimulated) ventricular muscle. In contrast to caffeine, tetnaethylammonium ions apparently did not mobilize cellular calcium.

It is suggested that the positive inotropic activity of tetraethylammonium ions is related to the observed alterations in the flux of calcium ions.