Cultured heart cells from the spontaneously diabetic KK mouse

In order to clarify the mechanism of myocardial changes in KK mice, cultured heart cells from both normal and spontaneously diabetic KK mice were studied by electron microscopy, photoelectric recording, and 45Ca activity. Compared with cultured heart cells from normal mice, those from KK mice showed a decrease in beating frequency and ceased beating more rapidly. The rhythm of the beating cells from KK mice became irregular, while that of the heart cells from normal mice was not changed significantly over a period of 10 days. Electron micrographs of cultured heart cells from KK mice showed an increased number of mitochondria, an intricate arrangement of myofibrils, poorly formed Z bands, and a lipidlike substance. The 45Ca activity of heart cells from KK mice, after incubation for 24 h in a medium containing 45Ca, was increased compared with heart cells from normal mice. Based on these findings, we conclude that ultrastructural alterations exist in cultured heart cells from KK mice and we suggest that an increase of intracellular Ca might play an important role in the pathogenesis.