Intron polymorphism in<i> Camk2d</i> is associated with ventricular arrhythmias in normal adult Sprague-Dawley rats

Calcium/calmodulin-dependent protein kinase II (CAMKII) is a critical regulator of cardiac electrophysiology. However, the role of the four bases deletion polymorphism in Camk2d which codes delta subunit of CAMKII, particularly those involving intron sequences, remains poorly understood. This study aimed to investigate the impact of Camk2d c.1044+125_128delGTTT missing polymorphism on cardiac morphology and arrhythmogenesis in normal adult Sprague-Dawley (SD) rats. A total of 85 SD rats were genotyped by Sanger sequencing, revealing a distribution of 25.9% wild-type (WT), 48.2% heterozygous, and 25.9% homozygous variants. Echocardiography, Hematoxylin-Eosin staining, Masson's trichrome staining and transmission electron microscopy indicated no significant differences in cardiac structure or baseline function among the three groups. In freely moving rats, premature atrial arrhythmias were detected in 2 of 9 WT rats, 1 of 9 heterozygous rats, and 1 of 9 homozygous rats. Premature ventricular contractions (PVCs) were observed in none of 9 WT or homozygous rats, 3 of 9 heterozygous rats, with one heterozygous rat exhibiting frequent PVCs. Electrical programmed stimulation revealed a higher incidence of inducible atrial fibrillation in homozygous rats compared to WT rats and a higher incidence of inducible ventricular tachycardia in heterozygous rats compared to WT rats. These findings suggest that deletion polymorphism in the intron sequences of Camk2d are unexpectedly common in normal SD rat populations and that such polymorphism predispose to ventricular arrhythmias without overt structural heart disease. Our study highlights the potential arrhythmogenic risk associated with non-coding DNA sequence alterations in Camk2d and underscores the importance of genetic screening in experimental animal models.