Functional interaction between InsP3 receptors and store-operated Htrp3 channels

Area of Science:

• Cellular Biology
• Molecular Signaling
• Ion Channel Physiology

Background:

• Calcium ions (Ca2+) are crucial intracellular messengers released from stores upon stimulation.
• Store depletion triggers Ca2+ influx via store-operated channels (SOC) and Ca2+-release-activated current (I(crac)).
• The mechanism linking Ca2+ store depletion to SOC/I(crac) activation remains debated, with models proposing messenger molecules or direct receptor coupling.

Purpose of the Study:

• To investigate the functional interaction between the store-operated channel Htrp3 and inositol 1,4,5-trisphosphate (InsP3) receptors.
• To determine if InsP3 receptors directly regulate SOC and I(crac) activity in response to Ca2+ store depletion.
• To provide evidence supporting the coupling hypothesis of calcium signaling.

Main Methods:

• Stable expression of mammalian Htrp3 channels in HEK293 cells.
• Electrophysiological recordings of SOC and I(crac) in intact and excised membrane patches.
• Stimulation with InsP3 and assessment of channel activity following Ca2+ store depletion and receptor washing.

Main Results:

• Htrp3 channels exhibited tight functional interaction with InsP3 receptors.
• Htrp3 channel activation was observed upon Ca2+ mobilization in intact cells and direct InsP3 application in excised patches.
• InsP3-induced Htrp3 activation, lost upon washing, was restored by adding InsP3-bound InsP3 receptors.

Conclusions:

• The findings provide strong evidence for the coupling hypothesis in calcium signaling.
• InsP3 receptors, upon activation by InsP3, directly interact with and regulate store-operated calcium channels (SOC).
• This direct interaction mechanism is critical for controlling Ca2+ influx following intracellular store depletion.