Quinolinic acid: a modulator of the heart calcium channel in the rat and a binder of calcium ions.

When rat heart preparations were perfused with quinolinic acid at a slow constant rate, a decrease in contractility was observed. A higher rate of perfusion resulted in a biphasic response, thus both a positive inotropic effect and then a decrease in heart contractility were visible. Using a polarographic method, the association constant of quinolinic acid with calcium ions (Ka) was found to be equal to 220. By combining the values from heart perfusion experiments with the calculated ones of free calcium ions, a linear correlation was obtained between the decreases of contractility and of calcium ions (r = 0.94).