Wang Yan, Morishima Masaki, Ono Katsushige
Department of Pathophysiology, Oita University School of Medicine, Oita 879-5593, Japan.
Department of Cardiology and Clinical Examination, Faculty of Medicine, Oita University, Oita 870-1192, Japan.
Membranes (Basel). 2022 Jul 2;12(7):686. doi: 10.3390/membranes12070686.
Two distinct isoforms of the T-type Ca channel, Cav3.1 and Cav3.2, play a pivotal role in the generation of pacemaker potentials in nodal cells in the heart, although the isoform switches from Cav3.2 to Cav3.1 during the early neonatal period with an unknown mechanism. The present study was designed to investigate the molecular system of the parts that are responsible for the changes of T-type Ca channel isoforms in neonatal cardiomyocytes using the whole-cell patch-clamp technique and mRNA quantification. The present study demonstrates that PKC activation accelerates the Ni-sensitive beating rate and upregulates the Ni-sensitive T-type Ca channel current in neonatal cardiomyocytes as a long-term effect, whereas PKC inhibition delays the Ni-sensitive beating rate and downregulates the Ni-sensitive T-type Ca channel current. Because the Ni-sensitive T-type Ca channel current is largely composed of the Cav3.2-T-type Ca channel, it is accordingly assumed that PKC activity plays a crucial role in the maintenance of the Cav3.2 channel. The expression of Cav3.2 mRNA was highly positively correlated with PKC activity. The expression of a transcription factor Nkx2.5 mRNA, possibly corresponding to the Cav3.2 channel gene, was decreased by an inhibition of PKCβII. These results suggest that PKC activation, presumably by PKCβII, is responsible for the upregulation of Ca3.2 T-type Ca channel expression that interacts with a cardiac-specific transcription factor, Nkx2.5, in neonatal cardiomyocytes.
T型钙通道的两种不同亚型Cav3.1和Cav3.2在心脏节点细胞起搏电位的产生中起关键作用，尽管在新生儿早期亚型会从Cav3.2转换为Cav3.1，但其机制尚不清楚。本研究旨在利用全细胞膜片钳技术和mRNA定量分析，研究新生儿心肌细胞中负责T型钙通道亚型变化的分子系统。本研究表明，蛋白激酶C（PKC）激活可加速新生儿心肌细胞中镍敏感性搏动频率，并上调镍敏感性T型钙通道电流，这是一种长期效应，而PKC抑制则会延迟镍敏感性搏动频率并下调镍敏感性T型钙通道电流。由于镍敏感性T型钙通道电流主要由Cav3.2-T型钙通道组成，因此推测PKC活性在维持Cav3.2通道中起关键作用。Cav3.2 mRNA的表达与PKC活性高度正相关。抑制PKCβII可降低可能对应于Cav3.2通道基因的转录因子Nkx2.5 mRNA的表达。这些结果表明，可能由PKCβII介导的PKC激活负责上调Ca3.2 T型钙通道的表达，该通道在新生儿心肌细胞中与心脏特异性转录因子Nkx2.5相互作用。
