抄録
Cardiomyocytes derived from mouse embryonic stem (mES) cells have been demonstrated a time-dependent expression of ion channels and signal transduction pathways. However, Na+/Ca2+ exchangers (NCX), which play crucial roles for cardiac functions, have not been well elucidated. In this study, we investigated the functional expression of NCX in mES cells at various stages of in vitro differentiation into cardiomyocytes. When NCXs were blocked by 100 μM KB-R7943, the dynamic changes in [Ca2+]i were observed in almost all mES cells, which showed two different patterns, namely a [Ca2+]i transient and a sustained elevation of [Ca2+]i. A [Ca2+]i transient was observed in 90% of undifferentiated mES cells but few derived cardiomyocytes. In contrast, a sustained elevation of [Ca2+]i was observed in derived cardiomyocytes and [Ca2+]i increased in a time course of differentiation. By RT-PCR the expression levels of a NCX1 mRNA increased during the differentiation. When Na+ pumps were blocked by ouabain, [Ca2+]i oscillations could be induced in 75% of derived cardiomyocytes at the middle stage of differenitation but not at the earlier stages, indicating the functional coupling of NCXs with Na+ pumps. Taken together, we conclude that the contribution of NCXs to lowing [Ca2+]i become greater during differentiation and the functional coupling with Na+ pumps is established at the middle stage of the differentiation. [Jpn J Physiol 54 Suppl:S98 (2004)]
