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Ca 2+ sparks in mammalian skeletal muscle can be activated locally by focal photolysis of BiNiX, a new caged caffeine analog
Author(s) -
Ward Christopher William,
Kao Joseph P.Y.,
Lederer Jonathan,
Ni Jiahong,
Rodney George G.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1357-b
Subject(s) - ryanodine receptor , photodissociation , chemistry , biophysics , caffeine , myocyte , skeletal muscle , microbiology and biotechnology , biochemistry , endoplasmic reticulum , anatomy , photochemistry , biology , endocrinology
Ca 2+ sparks arise when clusters of ryanodine receptors (RyR) are activated. They are, however, normally suppressed in intact mammalian muscle. To investigate the biophysical basis of Ca 2+ spark suppression/activation, we imaged myofibers loaded with the Ca 2+ indicator fluo‐4 on a confocal microscope. In addition, we applied a cell‐permeable caged caffeine analog (BiNiX). Spatially restricted (<20μm) photolysis of BiNiX (4,5‐ Bis (carboxymethyl)‐2‐nitrobenzyl‐paraxanthine) was produced by a single sub‐millisecond pulse of UV laser illumination (355 nm). We sought to (1) Determine if spatially restricted photolysis of BiNiX could promote the appearance of Ca 2+ sparks in permeablized adult or early postnatal intact myofibers which do exhibit rare Ca 2+ sparks. (2) Determine if localized modulation of CICR potential by photolysis of BiNiXcould overcome the suppression of Ca 2+ sparks in structurally intact adult mammalian myofibers which normally never exhibit Ca 2+ sparks. In permeabilized mammalian myofibers (which do have Ca 2+ sparks), photolysis of BiNiX is effective at eliciting a localized SR release flux and of activating Ca 2+ sparks. In addition, in intact developing myofibers (which exhibit rare Ca 2+ sparks), BiNiX photolysis significantly increased the occurrence of Ca 2+ sparks. In contrast, in intact adult myofibers BiNiX photolysis was unable to elicit Ca 2+ sparks despite evidence for regional propagation of CICR. We conclude that in intact adult mammalian myofibers RyR1, activation by BiNiX is unable to relieve the suppression of Ca 2+ sparks; a result most consistent with DHPR suppression of Ca 2+ sparks.