William C Lester

Publications (6) View all

• Source

  Available from: William C Lester

  Dataset: William Lester -supplement-02

  William C Lester, Elizabeth A Schroder, Don E Burgess, Doug Yozwiak, Douglas A Andres, Jonathan Satin
• Source

  Available from: William C Lester

  Dataset: William Lester -supplement-02

  William C Lester, Elizabeth A Schroder, Don E Burgess, Doug Yozwiak, Douglas A Andres, Jonathan Satin
• Source

  Available from: William C Lester

  Conference Proceeding: AHA Basic Cardiovascular Sciences, (2009), Circ. Research

  William C. Lester, Jonathan Satin
  [show abstract] [hide abstract]
  ABSTRACT: Calcium handling contributes to excitability, contractility and cell signaling, and developing cardiac myocytes require simultaneous control of all three of these properties. However, mechanisms controlling Ca-handling in developing cardiac myocytes are poorly resolved. The goal of this study is to test the hypothesis that the fundamental Ca-induced Ca2�-release machinery functions in embryonic ventricular myocytes (EVM) similarly to that in the adult (AVM). Using high speed 2-dimensional Ca-imaging we show that diastolic sparks exist in E16 ventricular myocytes (EVM), and are L-type channel (Cav1.2) Ca-entry dependent. EVM do not have t-tubules in register as in AVM, but in EVM Di-8-ANEPPS immunostaining appeared in a punctuate pattern in x, y, and z-planes. Diastolic sparks are defined as those Ca2� sparks observed after relaxation, and before the onset of the subsequent contraction. EVM diastolic spark size was symmetrical in 2-dimensions and was indistinguishable from AVM spark size (EVM, FWHMx = 2.25 +/- 0.01 um, FWHMy = 2.25 +/- 0.01 um, n=81, AVM, FWHMx = 2.33 +/- 0.02 um, FWHMy = 2.32 +/- 0.02 um, n = 81). EVM diastolic sparks werenot sub-cell-location-specific (peripheral = 83, central = 75, n = 20). AVM diastolic spark amplitude was significantly larger than EVM (p<0.001, n=70). Surprisingly, the rate of rise of the EVM diastolic spark was significantly faster than AVM (p<0.001, n=70). Indistinguishable EVM and AVM diastolic spark spatial dimensions argue for common release unit machinery. The presence of nascent t-tubules, CaV1.2, and RyR2 argue for mature Ca-release units. The more rapid rise of EVM Ca-sparks suggests that junctional sarcoplasmic reticulum exists with more coordinated Ca-release. We conclude that despite the lack of mature cytoarchitecture, early developing cardiac myocytes display mature functional units.
  AHA Basic Cardiovascular Sciences 2009, Las Vegas, Nevada; 09/2009
• Source

  Available from: William C Lester

  Article: Steady-state coupling of plasma membrane calcium entry to extrusion revealed by novel L-type calcium channel block.

  William C Lester, Elizabeth A Schroder, Don E Burgess, Doug Yozwiak, Douglas A Andres, Jonathan Satin
  [show abstract] [hide abstract]
  ABSTRACT: The L-type Ca2+ channel (Ca(v)1.2) is the main pathway for trans-sarcolemmal (SL) Ca2+ influx in cardiac myocytes. To maintain Ca2+ homeostasis, chronic SL Ca(2+)-influx must be matched by chronic SL efflux. In this study we tested the hypothesis that chronic downregulation of SL Ca2+ entry regulates SL extrusion. We studied mRNA and Ca2+ handling responses to chronic down-regulation of Ca2+ channel current induced by over-expression of the small GTPase Rem. Rem lowered net SL diastolic Ca2+ entry, and reduced the twitch Ca2+ amplitude. Rem also significantly slowed Ca2+ transient decay kinetics (p < 10(-3)). Rem reduced NCX1.1 protein level and function. To measure Na-Ca2+ exchange (NCX) function and sarcoplasmic reticulum (SR) store load we perfused Ca(2+)-free bath for 25s followed by rapid application of 50 mM caffeine. In control, caffeine transient relaxations were described by a bi-exponential decay with a fast phase that was 10 mM Ni(2+)-sensitive. Rem significantly slowed caffeine-induced relaxation time course (Rem versus control, p < 10(-6)). To test whether extrusion slowing was mediated by insufficient basal Ca2+ for allosteric NCX activation we measured the effect of increasing bath Ca2+ from 1.8 to 6 mM on caffeine-induced relaxation kinetics. 6 mM Ca2+ did not alter kinetics of control cells, but in Rem-over-expressed cells 6 mM Ca2+ sped kinetics. We conclude that chronic block of Ca(v)1.2 channel-mediated SL entry alters NCX expression, and coincidentally controls SR Ca loading and SL Ca2+ efflux.
  Cell Calcium 11/2008; 44(4):353-62. · 3.77 Impact Factor
• Source

  Available from: William C Lester

  Article: L-type calcium channel alpha-subunit and protein kinase inhibitors modulate Rem-mediated regulation of current.

  Shawn M Crump, Robert N Correll, Elizabeth A Schroder, William C Lester, Brian S Finlin, Douglas A Andres, Jonathan Satin
  [show abstract] [hide abstract]
  ABSTRACT: Cardiac voltage-gated L-type Ca channels (Ca(V)) are multiprotein complexes, including accessory subunits such as Ca(V)beta2 that increase current expression. Recently, members of the Rad and Gem/Kir-related family of small GTPases have been shown to decrease current, although the mechanism remains poorly defined. In this study, we evaluated the contribution of the L-type Ca channel alpha-subunit (Ca(V)1.2) to Ca(V)beta2-Rem inhibition of Ca channel current. Specifically, we addressed whether protein kinase A (PKA) modulation of the Ca channel modifies Ca(V)beta2-Rem inhibition of Ca channel current. We first tested the effect of Rem on Ca(V)1.2 in human embryonic kidney 293 (HEK-293) cells using the whole cell patch-clamp configuration. Rem coexpression with Ca(V)1.2 reduces Ba current expression under basal conditions, and Ca(V)beta2a coexpression enhances Rem block of Ca(V)1.2 current. Surprisingly, PKA inhibition by 133 nM H-89 or 50 microM Rp-cAMP-S partially relieved the Rem-mediated inhibition of current activity both with and without Ca(V)beta2a. To test whether the H-89 action was a consequence of the phosphorylation status of Ca(V)1.2, we examined Rem regulation of the PKA-insensitive Ca(V)1.2 serine 1928 (S1928) to alanine mutation (Ca(V)1.2-S1928A). Ca(V)1.2-S1928A current was not inhibited by Rem and when coexpression with Ca(V)beta2a was not completely blocked by Rem coexpression, suggesting that the phosphorylation of S1928 contributes to Rem-mediated Ca channel modulation. As a model for native Ca channel complexes, we tested the ability of Rem overexpression in HIT-T15 cells and embryonic ventricular myocytes to interfere with native current. We find that native current is also sensitive to Rem block and that H-89 pretreatment relieves the ability of Rem to regulate Ca current. We conclude that Rem is capable of regulating L-type current, that release of Rem block is modulated by cellular kinase pathways, and that the Ca(V)1.2 COOH terminus contributes to Rem-dependent channel inhibition.
  AJP Heart and Circulatory Physiology 11/2006; 291(4):H1959-71. · 3.71 Impact Factor