Ultrastructural localization of calcium deposits in rat myocardium after loud noise exposure.

In previous studies we demonstrated that loud noise exposure induces ultrastructural alterations in the rat myocardium together with an increase in noradrenergic activity and in mitochondrial calcium influx. To verify the causal relationship between myocardial calcium entry and ultrastructural alterations induced by loud noise, in the present study we coupled routine electron microscopy with cytochemistry specifically dedicated to visualize calcium accumulation (revealed as antimonate deposits). We observed that the ultrastructural alterations occurring in both atrium and ventricle after 12 h of noise exposure, were densely packed with antimonate deposits. In particular, enlargements of the sarcoplasmic reticulum and dilution of the mitochondrial matrix, observed during routine electron microscopy, were markedly positive for calcium accumulation when observed by using antimonate. The present data strongly suggest that calcium entry results in accumulation of this ion at myocardial subcellular level. Moreover, the present results joined with previous evidence indicate that calcium accumulation is the final common pathway responsible for noise-induced myocardial morphological alterations.