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Articles by R. A. Li
Total Records ( 2 ) for R. A. Li
  J Liu , D. K Lieu , C. W Siu , J. D Fu , H. F Tse and R. A. Li
 

Cardiomyocytes (CMs) are nonregenerative. Self-renewable pluripotent human embryonic stem cells (hESCs) can differentiate into CMs for cell-based therapies. We recently reported that Ca2+ handling, crucial to excitation-contraction coupling of hESC-derived CMs (hESC-CMs), is functional but immature. Such immature properties as smaller cytosolic Ca2+ transient amplitudes, slower kinetics, and reduced Ca2+ content of sarcoplasmic reticulum (SR) can be attributed to the differential developmental expression profiles of specific Ca2+ handling and regulatory proteins in hESC-CMs and their adult counterparts. In particular, calsequestrin (CSQ), the most abundant, high-capacity but low-affinity, Ca2+-binding protein in the SR that is anchored to the ryanodine receptor, is robustly expressed in adult CMs but completely absent in hESC-CMs. Here we hypothesized that gene transfer of CSQ in hESC-CMs suffices to induce functional improvement of SR. Transduction of hESC-CMs by the recombinant adenovirus Ad-CMV-CSQ-IRES-GFP (Ad-CSQ) significantly increased the transient amplitude, upstroke velocity, and transient decay compared with the control Ad-CMV-GFP (Ad-GFP) and Ad-CMV-CSQ-IRES-GFP (Ad-CSQ, which mediated the expression of a nonfunctional, truncated version of CSQ) groups. Ad-CSQ increased the SR Ca2+ content but did not alter L-type Ca2+ current. Pharmacologically, untransduced wild-type, Ad-GFP-, Ad-CSQ-, and Ad-CSQ-transduced hESC-CMs behaved similarly. Whereas ryanodine significantly reduced the Ca2+ transient amplitude and slowed the upstroke, thapsigargin slowed the decay. Neither triadin nor junctin was affected. We conclude that CSQ expression in hESC-CMs facilitates Ca2+ handling maturation. Our results shed insights into the suitability of hESC-CMs for therapies and as certain heart disease models for drug screening.

  P Jiang , S. N Rushing , C. w Kong , J Fu , D. K. T Lieu , C. W Chan , W Deng and R. A. Li
 

Human embryonic stem cells (hESCs) can self-renew while maintaining their pluripotency. Direct reprogramming of adult somatic cells to induced pluripotent stem cells (iPSCs) has been reported. Although hESCs and human iPSCs have been shown to share a number of similarities, such basic properties as the electrophysiology of iPSCs have not been explored. Previously, we reported that several specialized ion channels are functionally expressed in hESCs. Using transcriptomic analyses as a guide, we observed tetraethylammonium (TEA)-sensitive (IC50 = 3.3 ± 2.7 mM) delayed rectifier K+ currents (IKDR) in 105 of 110 single iPSCs (15.4 ± 0.9 pF). IKDR in iPSCs displayed a current density of 7.6 ± 3.8 pA/pF at +40 mV. The voltage for 50% activation (V1/2) was –7.9 ± 2.0 mV, slope factor k = 9.1 ± 1.5. However, Ca2+-activated K+ current (IKCa), hyperpolarization-activated pacemaker current (If), and voltage-gated sodium channel (NaV) and voltage-gated calcium channel (CaV) currents could not be measured. TEA inhibited iPSC proliferation (EC50 = 7.8 ± 1.2 mM) and viability (EC50 = 5.5 ± 1.0 mM). By contrast, 4-aminopyridine (4-AP) inhibited viability (EC50 = 4.5 ± 0.5 mM) but had less effect on proliferation (EC50 = 0.9 ± 0.5 mM). Cell cycle analysis further revealed that K+ channel blockers inhibited proliferation primarily by arresting the mitotic phase. TEA and 4-AP had no effect on iPSC differentiation as gauged by ability to form embryoid bodies and expression of germ layer markers after induction of differentiation. Neither iberiotoxin nor apamin had any function effects, consistent with the lack of IKCa in iPSCs. Our results reveal further differences and similarities between human iPSCs and hESCs. A better understanding of the basic biology of iPSCs may facilitate their ultimate clinical application.

 
 
 
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