Thimerosal Interacts with the Ca2+ Release Channel Ryanodine Receptor from Skeletal Muscle Sarcoplasmic Reticulum

Abstract

The thiol-oxidizing reagent, thimerosal, has been shown to increase the intracellular Ca2+ concentration, to induce Ca2+ spikes in several cell types, and to increase the sensitivity of intracellular Ca2+ stores to inositol 1,4,5-trisphosphate. Ryanodine-sensitive stores have also been implicated in the generation of Ca2+ oscillations induced by the addition of thimerosal. Here we report that micromolar concentrations of thimerosal stimulate Ca2+ release from skeletal muscle sarcoplasmic reticulum vesicles, inhibit high affinity [3H]ryanodine binding, and modify the channel activity of the reconstituted Ca2+ release protein. Thimerosal inhibits ryanodine binding by decreasing the binding capacity (Bmax) but does not affect the binding affinity or the dissociation rate of bound ryanodine. Single channel reconstitution experiments show that thimerosal (100-200 microM) stimulates single channel activity without modifying channel conductance. The thimerosal-stimulated channel is not inhibited by heparin. Furthermore, a Ca(2+)-stimulated channel is first activated and then inhibited in a time-dependent fashion by high concentrations of thimerosal (1 mM). Once inactivated, the channel cannot be reactivated by addition of either Ca2+ or ATP.

Uncoupling of ATP-Mediated Calcium Signaling and Dysregulated Interleukin-6 Secretionin Dendritic Cells by Nanomolar Thimerosal

“…RyR1 is also a sensitive target of THI ( Figure 3E ) ( Abramson et al 1995 ). We show that ATP triggers a Ca 2+ transient in IDCs whose temporal property relies on functional coupling of IP 3 R and RyR1 channels that is extremely sensitive to THI (≤ 100 nM).…”

“…THI-mediated attenuation of IL-6 secretion at 0.2 μM ATP was not unexpected because the suboptimal calcium signals induced by 0.2 μM ATP may not have been sufficient to promote maximal rates of IL-6 synthesis. Ca 2+ -stimulated RyR1 channels are initially activated and then inactivated by THI ( Figure 3F ) ( Abramson et al 1995 ). Over the 20 hr assay used in this study, the uncoupling of IP 3 R–RyR1 functions is likely to have broad effects upon Ca 2+ -dependent processes.…”

“…THI contains an oxidized mercury atom (Hg 2+ ) whose redox properties can enhance the activity of the inositol 1,4,5-trisphosphate receptor (IP 3 R) and ryanodine receptor (RyRs), both intracellular Ca 2+ channels ( Kaplin et al 1994 ; Pessah et al 2002 ). THI elicits Ca 2+ release from ER/SR stores in lymphocytes ( Bultynck et al 2004 ) and ER/SR microsomes by targeting the IP 3 R and RyR ( Abramson et al 1995 ; Kaplin et al 1994 ). THI-treated, monocyte-derived DCs failed to or only minimally phosphorylated STAT (signal transducer and activator of transcription) proteins 1, 3, 4, and 6, implying that the JAK (janus kinase) signaling pathway and, by extension, cytokine receptors are bypassed in the sensitization phase induced by THI ( Valk et al 2002 ).…”

Reactive Oxygen Species: Impact on Skeletal Muscle

“…The redox influence on sarcoplasmic reticulum (SR) function has been investigated in both cardiac and skeletal muscle (2, 3, 23, 253, 348, 413, 420, 431). The ryanodine receptor (RyR) calcium release channel in the SR is a large homotetramer composed of four 565-kDa subunits.…”

Single-cell resolution of intracellular T cell Ca2+dynamics in response to frequency-based H2O2stimulation

“…However, it is often difficult to measure intracellular ROS and many techniques only allow for population averages through time. There is known cross talk between calcium and H 2 O 2 during T cell activation; ROS, including H 2 O 2 , is able to activate calcium release channels 16–18 and increase the channel activity of two ER membrane channels, IP 3 R and RyR 19–23 , while NADPH oxidases Duox1/2 24 and many mitochondrial proteins (e.g. VDAC) are calcium sensitive 25 .…”