Experimental protocol
A target of 6 samples of each cardiac tissue were assigned at random to one of four concentrations of chloroquine base (1, 10, 30 or 100 µM, dissolved in Krebs solution) in the presence of the vehicle for diazepam (1% v/v propylene glycol). Spontaneously beating right atria were exposed only to 30 µM chloroquine. In a separate experiment, fresh tissues (target of 6 per group) were incubated with diazepam at concentrations of 1, 10 or 100 µM for 30 minutes before the addition of 30 µM chloroquine.