Abstract 5348: T-type Ca2+ Channels Play A Crucial Role In The Development Of Cardiac Automaticity And Conduction-system: Implication Of Their Time- And Space-dependent Expression
(Background) T-type Ca2+ channels encoded by Cav3.1 or Cav3.2 are abundantly expressed in cardiac pacemaker cells and conduction-system cells to play the pivotal role for cardiac automaticity. The expressions are developmentally regulated, as indicated by their higher density in embryonic heart than in adult heart, however, the precise expressions in a time- and space-dependent manner are unknown during differentiation to heart.
(Materials and Methods) To investigate the expression in a time dependent manner, we used Nkx2.5/GFP(+) cardiac progenitor cells derived from mouse embryonic stem (ES) cell, sorted from the embryonic bodies (EBs) with flow cytometers. The current density of each channel was measured by patch-clamp techniques. Moreover we used whole mount in situ hybridization (WISH) technique to investigate the distribution in a space dependent manner.
(Results) On the day 7.5 after Nkx2.5/GFP(+) ES cells differentiation, the EBs started the self-directive beating, and the cells predominantly revealed the transcription of Cav3.2 mRNA and the α1H protein expression to induce the Ni+ sensitive Ca2+ current and automaticity of their action potentials. While on the day 10.5, the cells predominantly revealed the transcription of Cav3.1 mRNA and the α1G protein expression to loose their Ni+ sensitive Ca2+ current and automaticity, indicating that there was the subtype switching of Type Ca2+ channels from Cav3.2 to Cav3.1 during the heart differentiation. In the WISH experiments, Cav3.2 was predominantly expressed on the day 8.5 embryonic heart, while both Cav3.1 and Cav3.2 were expressed on the day 10.5. Interestingly on the day 10.5, the four chambers were formed in the heart, the distribution of Cav3.1 was overlapped with that of MinK, which was known as a marker of conduction system to predominantly distribute in the atrio-ventricular canal alone, while the distribution of Cav3.2 was overlapped with that of not only MinK but also Isl1, a marker of the pace-making cells, of which expression was predominantly distributed in the outflow tract alone.
(Conclusion) Cav3.2 played critical roles of the development of pace making in embryonic heart, while Cav3.1 was involved in the development of cardiac conduction-system together with Cav3.2.