Species variation in arterial-myocardial sensitivity to verapamil

The changes in tension with increasing calcium concentration were examined in papillary muscles isolated from cats, rabbits, and rats, and in isolated rat atria. Similar curves were determined for cat femoral artery and lower descending aorta from rabbits and rats. In all tissues, the concentration of verapamil (KB) was determined which achieved a calcium dose ratio of 2. Rat myocardium was the most (KB = 3.38 +/- 0.18 X 10(-6) mol . litre-1) and rabbit the lest (KB = 1.18 +/- 0.01 X 10(-5) mol . litre-1) sensitive to verapamil. Cat tissue was intermediate; rat atria and ventricle were similar. By contrast, arterial sensitivity was always greater with arterial-myocardial sensitivity ratios varying from 175 +/- 7 in the cat to 1073 +/- 97 in the rabbit. This technique is a formal evaluation of the arterial-myocardial sensitivity of calcium entry blockers and may permit prediction of the myocardial and vasodilator properties of novel compounds.