Colocalization of dihydropyridine and ryanodine receptors in developing heart with a neural crest-associated defect

Neural crest-associated congenital heart defects in humans are among the most lethal and costly to treat. In avian and mouse embryos with persistent truncus arteriosus (PTA), the most severe of the neural crest anomalies, there is poor cardiac function because of impaired excitation-contraction coupling. One possible explanation for poor excitation-contraction coupling is that peripheral junctions, composed of closely associated sarcoplasmic reticulum Ca(2+) release channels (ryanodine receptors) and surface membrane L-type Ca(2+) channels (dihydropyridine receptors), are not well colocalized.

To compare the degree of colocalization of these two Ca(2+) channel proteins in isolated ventricular myocytes from normal hearts and hearts with PTA.

PTA was induced in the embryonic chick by laser ablation of the cardiac neural crest before migration from the neural tube. Immunofluorescent staining of dihydropyridine and ryanodine receptors along with computer-assisted image analysis was used to measure relative colocalization.

Dihydropyridine and ryanodine receptor colocalization was greater by 20% in embryos with PTA. Much of the increase appeared to result from a 14% increase in the area stained for ryanodine receptors. A third observation was that a high level of colocalization was maintained even after enzymatic dissociation in which the embryonic myocytes had typically lost their elongated appearance and assumed a spherical shape.

The increased colocalization of dihydropyridine and ryanodine receptors in hearts with PTA may be a compensatory response to a defect at the level of single Ca(2+) channel proteins. These results indicate the high degree of stability of sarcoplasmic reticulum junctional complexes.