Thiol-Reactive Agents Biphasically Regulate Inositol 1,4,5-Trisphosphate Binding and Ca2+ Release Activities in Bovine Adrenal Cortex Microsomes1

• Published in: Endocrinology (Philadelphia) Vol. 142; no. 6; pp. 2614 - 2621
• Main Authors: Poirier, Stéphane N, Poitras, Marc, Laflamme, Karina, Guillemette, Gaétan
• Format: Journal Article
• Language: English
• Published: Endocrine Society 01-06-2001
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endo.142.6.8195

Within all endocrine cells, the inositol 1,4,5-trisphosphate
(InsP3) receptor plays an important role in regulation of
the intracellular Ca2+ concentration. In the present study
we showed that a single short-term treatment with either
N-ethylmaleimide (known to decrease InsP3
receptor activity) or thimerosal (known to increase InsP3
receptor activity) caused time-dependent biphasic effects on the
InsP3 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 Ca2+ 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 Ca2+
release efficiency. Under these conditions, Western blot analyses
demonstrated that the level of InsP3 receptor protein was
not modified. Sequential treatments with thimerosal and the reducing
agent dithiothreitol showed that the InsP3 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 InsP3 receptor. These results
also support the contention that cellular mechanisms of thiol group
modification could play important roles in regulation of the
intracellular Ca2+ concentration.