The homeobox-containing gene Csx/Nkx2.5 codes several cardiac transcription factors and plays a critical role in early cardiogenesis. We investigated the effect of Csx/Nkx2.5 on the expression of cardiac ion channels using P19-derived cardiomyocytes. P19CL6 cells and P19CL6 cells with Csx/Nkx2.5 overexpression (P19CL6-Csx cells) were induced to differentiate into cardiomyocytes by treatment with dimethyl sulfoxide. Action potentials and membrane currents were measured by whole cell patch clamp at different differentiation stage: the early stage (1–5 days after beating had begun) and the late stage (10–15 days after beating). Expression of Csx/Nkx2.5 mRNA was increased as the differentiation stages advanced in both P19CL6 and P19CL6-Csx cells. In action potential configuration, maximal diastolic potentials in P19CL6-Csx cells exhibited more hyperpolarized potential (‒ 64.2 mV) than those in P19CL6 cells (‒ 54.8 mV, p < 0.01) in the early stage. In P19CL6 cells, among 6 different voltage-gated and ligand-operated K+ channels expressed during the early stage, the transient-outward K+ channel was most predominant. By overexpression of Csx/Nkx2.5, developmental decrease in the transient-outward K+ channel was suppressed. Homeobox-containing gene Csx/Nkx2.5 modifies the amount of distinct ionic channels, during differentiation periods, predominantly changing the expression of the transient-outward K+ channel.

Signal regulators during early cardiogenetic differentiation for the cellular automaticity are largely unknown. Our investigations were designed to clarify the role of transcription factors and their modulators in P19-derived cardiomyocytes to the expression of cardiac pacemaker ion channels. Transcription factors Csx/Nkx2.5 and GATA4 but not MEF2C were markedly inhibited by p38 MAP kinase inhibition in a distinct manner; expression but not phosphorylation of GATA4 was reduced by inhibition of p38 MAP kinase actions. In the presence of an ERK1/2,5 inhibitor PD98059 or a JNK MAP kinase inhibitor SP600125, P19 cells successfully differentiated into cardiomyocytes displaying spontaneous beatings with expression of three types of pacemaker ion channels. We demonstrate that acquisition of cellular automaticity and the expression of pacemaker ion channels are regulated by the transcription factors, Csx/Nkx2.5 and GATA4, through intracellular signals including p38 MAP kinase in the process of P19-derived pluripotent cells differentiation into cardiomyocytes.

The Ordovician carbonate reservoir is the most productive deep-earth reservoir in Tahe Oilfield and other oilfields in Tarim Basin. Exploration and production successes in recent years reveal a new reservoir type, namely faulted karst reservoirs, which is closely related to regional strike-slip faults and very different from the well-recognized paleo-karst reservoir. The paleo-karst reservoirs distribute mainly in weathering crust regions in the northern Tahe Oilfield. Their primary reservoir spaces are meter-scale caves and the fluid conduits are predominantly the unconformable surfaces. In production, paleo-karst reservoirs always have sufficient energy, therefore high productivity. The faulted karst reservoirs mainly develop in southern Tahe Oilfield, controlled by the different ordered strike slip faults and related dissolutions. Their reservoir space is smaller than which of paleo-karst reservoirs. The predominant fluid conduits in these reservoirs are the faults. In production, reservoirs along major strike-slip faults have sufficient energy, high productivity and slow watercut increase like paleo-karst reservoirs. While in areas with less strong energy, faulted karst reservoir exhibits weak productivityand rapid watercut increase, implying a rule of “big fault big reservoir, small fault small reservoir, no fault no reservoir. A comprehensive understanding of the geophysical features, distribution characteristics, reservoir property, and production behaviors of the two reservoir types will assist further exploration and production in Tahe Oilfield and other basins containing such reservoirs.