Differences in the regulation of RyR2 from human, sheep, and rat by Ca2+ and Mg2+ in the cytoplasm and in the lumen of the sarcoplasmic reticulum

Kafa Walweel, Jiao Li, Peter Molenaar, Mohammad Imtiaz, Anthony Quail, Cris dos Remedios, Nicole BEARD, Angela dulhunty, Dirk van Helden, Derek Laver

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Abstract

Regulation of the cardiac ryanodine receptor (RyR2) by intracellular Ca 2+ and Mg 2+ plays a key role in determining cardiac contraction and rhythmicity, but their role in regulating the human RyR2 remains poorly defined. The Ca 2+-and Mg 2+-dependent regulation of human RyR2 was recorded in artificial lipid bilayers in the presence of 2 mM ATP and compared with that in two commonly used animal models for RyR2 function (rat and sheep). Human RyR2 displayed cytoplasmic Ca 2+ activation (K a = 4 μM) and inhibition by cytoplasmic Mg 2+ (Ki = 10 μM at 100 nM Ca 2+) that was similar to RyR2 from rat and sheep obtained under the same experimental conditions. However, in the presence of 0.1 mM Ca 2+, RyR2s from human were 3.5-fold less sensitive to cytoplasmic Mg 2+ inhibition than those from sheep and rat. The K a values for luminal Ca 2+ activation were similar in the three species (35 μM for human, 12 μM for sheep, and 10 μM for rat). From the relationship between open probability and luminal [Ca 2+], the peak open probability for the human RyR2 was approximately the same as that for sheep, and both were ~10-fold greater than that for rat RyR2. Human RyR2 also showed the same sensitivity to luminal Mg 2+ as that from sheep, whereas rat RyR2 was 10-fold more sensitive. In all species, modulation of RyR2 gating by luminal Ca 2+ and Mg 2+ only occurred when cytoplasmic [Ca 2+] was <3 μM. The activation response of RyR2 to luminal and cytoplasmic Ca 2+ was strongly dependent on the Mg 2+ concentration. Addition of physiological levels (1 mM) of Mg 2+ raised the K a for cytoplasmic Ca 2+ to 30 μM (human and sheep) or 90 μM (rat) and raised the K a for luminal Ca 2+ to ~1 mM in all species. This is the first report of the regulation by Ca 2+ and Mg 2+ of native RyR2 receptor activity from healthy human hearts.

Original languageEnglish
Pages (from-to)263-271
Number of pages9
JournalJournal of General Physiology
Volume144
Issue number3
DOIs
Publication statusPublished - 2014

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