“In some preparations, quinidine at concentrations of 5 μmol/l and higher slowed the spontaneous activity by its direct membrane action even in the presence of carbachol.”
“In the presence of 0.1 μmol/l carbachol , the spontaneous activity of the atrioventricular nodal preparations was markedly inhibited, whereas subsequent addition of 1, 5 and 20 μmol/l quinidine restored automaticity in a concentration-dependent manner.”