Effects of the calcium antagonist gallopamil on the increase of myocardial extracellular potassium activity during LAD occlusion in dogs

The effects of calcium antagonists on extracellular potassium accumulation during global ischaemia in isolated perfused rat hearts

The effects of equipotent concentrations of diltiazem, verapamil, and nifedipine upon the accumulation of extracellular potassium [K+]out and the left ventricular pressure (LVP) were studied during global ischemia in isolated perfused rat hearts. Measurement of [K+]out and LVP were performed in two series of experiments. Diltiazem (2 x 10(-6), 3 x 10(-6), and 10(-5) M), verapamil (3 x 10(-8), 10(-7), and 3 x 10(-7) M), and nifedipine (3 x 10(-8), 10(-7), and 1.5 x 10(-7) M) were able to slow, in a concentration-dependent manner, the initial rate of rise of [K+]out without affecting the final plateau value of [K+]out reached at t = 5 to t = 10 minutes. Notably, at the lowest concentrations, which slightly influenced LVP diltiazem, verapamil, and to a lesser degree nifedipine, were still able to slow the rise in [K+]out. In addition, after preperfusion with low-calcium media [( Ca2+] from 1.8 to 1.3 or 0.9 mM), inducing similar negative inotropic effects as those of the calcium antagonists, the rise in [K+]out was not significantly influenced. Our data indicate that the ability to slow the rise in [K+]out is a specific characteristic of calcium antagonists that is independent of their negative inotropic effects.

Effects of gallopamil, diltiazem and nifedipine on the loss of K+ from ischaemic pig hearts

K+ release into the extracellular space was investigated during repeated 6-min coronary occlusions before and after the intravenous administration of cardiovascular active doses of gallopamil (0.02; 0.05 mg/kg), diltiazem (1.0; 2.0 mg/kg) or nifedipine (0.01; 0.05 mg/kg) to anaesthetized pigs. [K+]e was measured epicardially using silver valinomycin electrodes calibrated in vivo. During control occlusions [K+]e- rose steeply in all groups, from a pre-ischaemic baseline value of about 3.5 mmol/l reaching a plateau value within the ischaemic period. This response was reproducible in an untreated control group. Gallopamil reduced the ischaemic K+ efflux dose dependently and significantly 10 min after injection; the higher dose also did 60 min after injection. Diltiazem had less effect on K+ efflux 10 min after administration and an effect was no longer detectable after 60 min. Nifedipine did not significantly inhibit the ischaemic K+ loss. Besides these differences in the direct protection of the ischaemic myocardium, the Ca2+ antagonists also had the following effects on the haemodynamic profile. Diltiazem and gallopamil significantly prolonged PQ intervals whereas nifedipine caused a shortening accompanied by a significant increase in heart rate. Blood pressure and LV dP/dtmax were significantly reduced by all compounds, but to a different degree. Diltiazem reduced blood pressure to a greater extent than did nifedipine and gallopamil. LV dP/dtmax was comparably reduced by gallopamil and diltiazem, while nifedipine had less effect. Thus, gallopamil exerted pronounced protective effects on the ischaemic pig heart.