Comparison of the effectiveness of seven amiloride congeners as inhibitors of Na/H and Na/Ca antiport in cultured smooth muscle cells

The authors cultured smooth muscle cells from rat aorta and assayed Na/Ca antiport by measuring the initial rate of 45Ca influx in Na-loaded cells. Na/H antiport was assayed by measuring the initial rate of 22Na influx in acid-loaded cells. The external medium was the same for both assays except Na was 10 mM for Na/H antiport and O for the Na/Ca antiport assay. The dose of each congener that caused 50% inhibition (I50) was calculated using a log-log median effect plot. The linear regression coefficients ranged from 0.916 to 0.998. Of all the compounds tested only dimethylbenzamil is more potent as an inhibitor of Na/Ca compared to Na/H antiport