A probable role of dihydropyridine receptors in repression of Ca2+ sparks demonstrated in cultured mammalian muscle

Zhou, Jingsong, Yi, Jianxun, Royer, Leandro, Launikonis, Bradley S., Gonzalez, Adom, Garcia, Jesus and Rios, Eduardo (2006) A probable role of dihydropyridine receptors in repression of Ca2+ sparks demonstrated in cultured mammalian muscle. American Journal of Physiology - Cell Physiology, 290 2: C539-C553.


Author Zhou, Jingsong
Yi, Jianxun
Royer, Leandro
Launikonis, Bradley S.
Gonzalez, Adom
Garcia, Jesus
Rios, Eduardo
Title A probable role of dihydropyridine receptors in repression of Ca2+ sparks demonstrated in cultured mammalian muscle
Journal name American Journal of Physiology - Cell Physiology  (ERA 2012 Listed)    (ERA 2010 Rank A)   Check publisher's open access policy
Publication date 2006-02
Sub-type Article
DOI 10.1152/ajpcell.00592.2004
Volume number 290
Issue number 2
ISSN 0363-6143
Start page C539
End page C553
Total pages 15
Place of publication Bethesda, MD, U.S.A.
Publisher American Physiological Society
Language eng
Abstract To activate skeletal muscle contraction, action potentials must be sensed by dihydropyridine receptors (DHPRs) in the T tubule, which signal the Ca2+ release channels or ryanodine receptors (RyRs) in the sarcoplasmic reticulum (SR) to open. We demonstrate here an inhibitory effect of the T tubule on the production of sparks of Ca2+ release. Murine primary cultures were confocally imaged for Ca2+ detection and T tubule visualization. After 72 h of differentiation, T tubules extended from the periphery for less than one-third of the myotube radius. Spontaneous Ca2+ sparks were found away from the region of cells where tubules were found. Immunostaining showed RyR1 and RyR3 isoforms in all areas, implying inhibition of both isoforms by a T tubule component. To test for a role of DHPRs in this inhibition, we imaged myotubes from dysgenic mice (mdg) that lack DHPRs. These exhibited T tubule development similar to that of normal myotubes, but produced few sparks, even in regions where tubules were absent. To increase spark frequency, a high-Ca2+ saline with 1 mM caffeine was used. Wildtype cells in this saline plus 50 mu M nifedipine retained the topographic suppression pattern of sparks, but dysgenic cells in high-Ca2+ saline did not. Shifted excitation and emission ratios of indo-1 in the cytosol or mag-indo-1 in the SR were used to image [Ca2+] in these compartments. Under the conditions of interest, wild-type and mdg cells had similar levels of free [Ca2+] in cytosol and SR. These data suggest that DHPRs play a critical role in reducing the rate of spontaneous opening of Ca2+ release channels and/or their susceptibility to Ca2+-induced activation, thereby suppressing the production of Ca2+ sparks.
Keyword Cell Biology
Physiology
excitation-contraction coupling
sarcoplasmic reticulum
ryanodine receptors
Ca2+ imaging
Mouse Skeletal-muscle
Type-3 Ryanodine Receptors
Calcium-induced Release
Sarcoplasmic-reticulum
Elementary Events
Muscular Dysgenesis
Complementary-dna
Excitation
Fibers
Channel
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

 
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