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Direct activation of trpl cation channels by G alpha11 subunits
A G Obukhov1, C Harteneck, A Zobel
1Institut für Pharmakologie, Freie Universität Berlin, Germany.
Abstract:
G proteins of the Gq/11 subfamily functionally couple cell surface receptors to phospholipase C beta (PLC beta) isoforms. Stimulation of PLC beta induces Ca2+ elevation by inositol 1,4,5-trisphosphate (InsP3)-mediated Ca2+ release and store-dependent 'capacitative' Ca2+ entry through Ca(2+)-permeable channels. The Drosophila trp gene, as well as some human trp homologs, code for such store-operated channels. The related trp-like (trpl) gene product also forms a Ca(2+)-permeable cation channel, but is not activated by store depletion. Co-expression of the constitutively active Gq subfamily member G alpha 11 (G alpha 11) with trpl enhanced trpl currents 33-fold in comparison with co-expression of trpl with other G alpha isoforms or G beta gamma complexes. This activation could not be attributed to signals downstream of PLC beta. In particular, InsP3 infusion, modulation of protein kinase C activity or elevation of intracellular calcium concentration failed to induce trpl currents. In contrast, purified G alpha 11 (but not other G protein subunits) activated trpl channels in inside-out patches. We conclude that trpl is regulated by G11 proteins in a membrane-confined manner not involving cytosolic factors. Thus, G proteins of the Gq subfamily may induce Ca2+ entry not only indirectly via store-operated mechanisms but also by directly stimulating cation channels.
Insights
G alpha 11 proteins directly activate trp-like (trpl) cation channels, independent of phospholipase C beta signaling. This G protein interaction offers a novel mechanism for regulating calcium (Ca2+) entry.
Area of Science:
- Molecular Biology
- Cell Signaling
- Ion Channel Physiology
Background:
- G proteins of the Gq/11 subfamily link cell surface receptors to phospholipase C beta (PLC beta).
- PLC beta activation leads to calcium (Ca2+) elevation via inositol 1,4,5-trisphosphate (InsP3)-mediated release and store-operated Ca2+ entry.
- Drosophila trp and related human TRP channels function as store-operated Ca2+ channels, while trp-like (trpl) channels are Ca2+-permeable but not store-operated.
Purpose of the Study:
- To investigate the interaction between Gq/11 subfamily G proteins and the trp-like (trpl) cation channel.
- To determine if G alpha 11 can directly modulate trpl channel activity.
- To elucidate the mechanism by which G alpha 11 influences trpl currents.
Main Methods:
- Co-expression of trpl with various G alpha isoforms, including constitutively active G alpha 11, in a cellular system.
- Electrophysiological recordings (e.g., inside-out patch clamp) to measure trpl channel currents.
- Manipulation of downstream signaling molecules like InsP3 and protein kinase C activity.
Main Results:
- Co-expression of trpl with G alpha 11 significantly enhanced trpl currents (33-fold) compared to other G alpha isoforms or G beta gamma complexes.
- Activation of trpl by G alpha 11 was independent of PLC beta signaling, InsP3, protein kinase C, or elevated intracellular calcium.
- Purified G alpha 11 directly activated trpl channels in isolated membrane patches, indicating a direct, membrane-confined interaction.
Conclusions:
- The trp-like (trpl) cation channel is directly regulated by G proteins of the Gq subfamily, specifically G alpha 11.
- This regulation occurs in a membrane-confined manner, independent of cytosolic factors or downstream PLC beta signaling.
- G proteins of the Gq subfamily can mediate Ca2+ entry not only through indirect store-operated mechanisms but also by directly activating cation channels like trpl.