Exploring a novel role for zinc in modulation of sarcoplasmic reticulum calcium release in skeletal muscle

Gavin Robertson, Benedict Reilly O'Donnell, Samantha Jane Pitt

Research output: Contribution to conferenceAbstractpeer-review

Abstract

Aberrant Ca2+ release from sarcoplasmic reticulum Ca2+ stores due to dysfunction in the type-1 ryanodine receptor (RyR1) is implicated in the pathophysiology of muscular dystrophy (1). Recently it has been suggested that dynamic alterations in intracellular Zn2+ and Ca2+ homeostasis play a key role in the pathogenesis of dystrophies (2). The role of physiological levels of Zn2+ in modulating RyR1-channel gating has never been considered. We therefore set out to study the effects of Zn2+ on RyR1-channel function. RyR1 channels were prepared from guinea pig skeletal muscle and incorporated into planar phosphatidylethanolamine lipid bilayers under voltage-clamp conditions using previously described techniques (3). Single channel recordings were acquired under standard experimental conditions of 250 mM HEPES, 80 mM Tris, pH 7.2 (free [Ca2+] 10 µM) at the cytoplasmic face (cis-chamber) and 250 mM Glutamic acid, 10 mM HEPES, pH 7.2 with Ca(OH)2 (free [Ca2+] ≈50 mM) at the luminal (trans-chamber) face of the channel. The cis-chamber was held at 0 mV relative to ground. Channel open probability (Po) was determined over 3 minutes, and a Student's t-test used to determine statistical significance between mean values. Sequential addition of cytosolic Zn2+ in the range from 1 nM to 1 µM increased RyR1 Po in a dose dependent manner. Given that low concentrations of Zn2+ (10 nM) significantly increased channel Po from 0.018 ± 0.014 to 0.162 ± 0.038 (SEM, n=3, P<0.05) this indicates that Zn2+ has high affinity for RyR1. At concentrations above 1 µM the effect of Zn2+ appeared to inhibit channel activity. Regarding the mechanism of how Zn2+ modulates RyR1 function, we show that Zn2+ primarily increases Po by increasing the frequency of channel openings. The mean channel open time was 1.7 ± 0.5 in the absence and 2.1 ± 0.1, 2.3 ± 0.3, and 2.7 ± 0.5 ms (SEM, n = 3) in the presence of 1 nM, 10 nM and 100 nM Zn2+ respectively, suggesting that Zn2+ increases Po by sensitising the channel to cytosolic Ca2+. We also found that the presence of cytosolic Ca2+ (10 µM) was an absolute requirement for channel activation. At all Zn2+ doses that we tested (≤100 nM) lowering cytosolic Ca2+ to a sub-activating concentration (≈4 nM) by the addition of 1 mM BAPTA, reduced channel Po to zero (n=3). Our data reveal that Zn2+ is a high affinity effector of RyR1 that increases channel Po by modulating the sensitivity of the channel to cytosolic Ca2+. We suggest that perturbation of Zn2+-homeostasis will lead to aberrant Ca2+-release through inappropriate activation of RyR1 and that this will contribute to the pathophysiology of debilitating muscular wasting disorders such as muscular dystrophy. Where applicable, experiments conform with Society ethical requirements
Original languageEnglish
Publication statusPublished - 2015
EventPhysiology 2015 - Cardiff, United Kingdom
Duration: 6 Jul 20158 Jul 2015

Conference

ConferencePhysiology 2015
Country/TerritoryUnited Kingdom
CityCardiff
Period6/07/158/07/15

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