Electronmicroscopic autoradiographic study of the distribution of 3H-diltiazem in myocardial cells

The distribution of 3H-diltiazem in myocardial cell organelles was studied using an electronmicroscopic autoradiographic technique. At 3, 5 and 10 min after 3H-diltiazem injection, silver grains, which indicate the existence of diltiazem, were detected in plasma membranes and intracellular organelles. Silver grains in T systems were observed more frequently at 3 min than at 5 and 10 min. In contrast, silver grains in sarcoplasmic reticula and mitochondria apparently increased with the passage of time. These findings suggest that diltiazem is transported through the T system and may accumulate within the sarcoplasmic reticula and mitochondria. Furthermore, our study revealed morphologically for the first time that the intracellular sites of action where diltiazem was directed were possibly the mitochondria.