Calcium dobesilate and transmembrane potential in canine cardiac cells. A preliminary study

The electropharmacological effects of calcium 2,5-dihydroxybenzene sulfonate (calcium dobesilate, Doxium) were studied by means of intracellular microelectrode technique in order to measure the changes in action potentials (A.ps.) in dog isolated cardiac Purkinje fibers and the adjacent ventricular tissue superfused with Tyrode's solution. The addition of 25 mmol/l of calcium dobesilate to the superfusate suppressed automaticity in spontaneously functioning preparation. The frequency of the action potentials was decreased and their duration increased with elevation and prolongation of their plateau phase. These effects were produced in both Purkinje and adjacent ventricular fibers and they were reversed by washing out with Tyrode's solution. Addition of calcium (25 mmol/l) restored automaticity in preparation in which spontaneous activity had been previously arrested by tetrodotoxin (10(-4) mol/l). Calcium dobesilate-induced action potentials were slow i.e. with low dV/dtmax and were abolished by verapamil (10(-5) mol/l). Calcium dobesilate increased the contractile force in both normally working and tetrodotoxin-arrested preparations. These findings suggest that calcium dobesilate acts on the myocardial cell by promoting transmembrane calcium influx during the plateau phase through activation of the slow inward calcium current.