Thiol-Reactive Agents Biphasically Regulate Inositol 1,4,5-Trisphosphate Binding and Ca2+ Release Activities in Bovine Adrenal Cortex Microsomes*

Abstract

Within all endocrine cells, the inositol 1,4,5-trisphosphate (InsP(3)) receptor plays an important role in regulation of the intracellular Ca(2+) concentration. In the present study we showed that a single short-term treatment with either N-ethylmaleimide (known to decrease InsP(3) receptor activity) or thimerosal (known to increase InsP(3) receptor activity) caused time-dependent biphasic effects on the InsP(3) binding activity of bovine adrenal cortex microsomes. The early potentiating effect of thiol-reactive agents translated into a 2-fold increase in binding affinity and Ca(2+) release efficiency. The late dampening effect of thiol-reactive agents translated into a continuous reduction of the maximal binding capacity of the microsomes with a concomitant decrease in Ca(2+) release efficiency. Under these conditions, Western blot analyses demonstrated that the level of InsP(3) receptor protein was not modified. Sequential treatments with thimerosal and the reducing agent dithiothreitol showed that the InsP(3) receptor can readily oscillate between high and low affinity states that are related to its alkylation state. Our results suggest a common mode of action of thiol-reactive agents on the InsP(3) receptor. These results also support the contention that cellular mechanisms of thiol group modification could play important roles in regulation of the intracellular Ca(2+) concentration.

Pharmacology of inositol trisphosphate receptors

“…This inhibition develops more slowly than the stimulation [137]. Comparison of the effects of thimerosal on different cell types are compatible with the existence for IP 3 R1 of both a stimulatory and an inhibitory effect, whereas for IP 3 R3 only an inhibitory effect exists [113].…”

“…Thimerosal also stimulates IP 3 binding to the recombinantly expressed ligand-binding domain of IP 3 R1 suggesting that at least for IP 3 R1 the critical sulphydryl residues must be present in that domain [176]. In bovine adrenal cortex, expressing predominantly IP 3 R1, the early increase in IP 3 binding affinity induced by thimerosal is followed by a later reduction of the maximal binding capacity [137]. The cysteines involved are so far unknown.…”

Effect of thimerosal on Ca2+ movement and apoptosis in PC3 prostate cancer cells

“…Thimerosal induced Ca 2+ release of heat‐shocked porcine oocytes [Tseng and Ju, 2009] and stimulated histamine‐induced Ca 2+ release from endoplasmic reticulum in HeLa cells [Montero et al, 2001]. In bovine adrenal cortex microsomes, Poirier et al [2001] showed that thimerosal biphasically regulate inositol 1,4,5‐trisphosphate binding and Ca 2+ release activities. Similarly, Abramson et al [1995] suggested that thimerosal interacts with the Ca 2+ release channel ryanodine receptor from skeletal muscle sarcoplasmic reticulum.…”

“…Thimerosal is a mercury‐containing component found in many vaccine preparations and used as a preservative [Elferink, 1999; Geier et al, 2007]. It causes Ca 2+ movement across cell membrane in different cells [Poirier et al, 2001] that may be mediated via effects on ryanodine receptors [Dulhunty et al, 2000], sodium channels [Evans and Bielefeldt, 2000], Ca 2+ ‐activated K + currents [Lang et al, 2000], and L‐type Ca 2+ channels [Fearon et al, 1999].…”

Oxidation by Thimerosal Increases Calcium Levelsin Renal Tubular Cells

“…The ability of thimerosal to act on sulfhydryl group is related to the presence of mercury. Thimersal causes a release of Ca 2+ from intracellular stores in many cells types; this is accompanied by an influx of extracellular calcium, via oxidation of cell membrane proteins and other components (Pintado et al 1995; Chen et al 1998; Tornquist et al 1999; Montero et al 2001; Poirier et al 2001). Oxidation can alter many aspects of cell function, including Ca 2+ signaling (Sauer et al 2001).…”