Subtype Switching of T-Type Ca ²⁺ Channels From Cav3.2 to Cav3.1 During Differentiation of Embryonic Stem Cells to Cardiac Cell Lineage

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Background The developmental changes of Ni²⁺-sensitivity to automaticity of Nkx2.5-positive cells derived from mouse embryonic stem cell have been identified, suggesting developmental regulation of expressing Ni²⁺-sensitive T-type Ca²⁺ channel, although the mechanism of the change has not been fully studied. Methods and Results Transcripts of Cav3.2, Cav3.1 and Cav1.2 genes of beating Nkx2.5-positive cells, which encode the Ni²⁺-sensitive T-type Ca²⁺ channel, Ni²⁺-insensitive T-type Ca²⁺ channel, and L-type Ca²⁺ channel, respectively, were investigated by real-time reverse-transcriptase-polymerase chain reaction, and the current density of each channel was measured by patch-clamp techniques at the early and late stages of differentiation. The expression of the Cav3.2 transcript predominated in the early stage whereas those of Cav3.1 and Cav1.2 transcripts were upregulated in the late stage, which was consistent with the change in each current density, suggesting the expression of channel proteins is largely determined at the transcriptional level. Conclusion The results indicate that the mechanism of change of Ni²⁺-sensitivity is partly, if not completely, the subtype switch of T-type Ca²⁺ channel from Cav3.2 to Cav3.1 at the transcriptional level, and that the expression of the L-type Ca²⁺ channel might have an attenuating effect on Ni²⁺-sensitivity to automaticity in the late stage of differentiation. (Circ J 2005; 69: 1284 - 1289)