Activation of heterologously expressed Drosophila TRPL channels: Ca2+ is not required and InsP3 is not sufficient.

Abstract

Light-sensitive channels encoded by the Drosophila transient receptor potential-like gene (trpl) are activated in situ by an unknown mechanism requiring activation of Gq and phospholipase C (PLC). Recent studies have variously concluded that heterologously expressed TRPL channels are activated by direct Gq-protein interaction, InsP3 or Ca2+. In an attempt to resolve this confusion we have explored the mechanism of activation of TRPL channels co-expressed with a PLC-specific muscarinic receptor in a Drosophila cell line (S2 cells). Simultaneous whole-cell recordings and ratiometric Indo-1 Ca2+ measurements indicated that agonist (CCh)-induced activation of TRPL channels was not always associated with a rise in Ca2+. Internal perfusion with BAPTA (10 mM) reduced, but did not block, the response to agonist. In most cases, releasing caged Ca2+ facilitated the level of spontaneous channel activity, but similar concentrations (200-500 nM) could also inhibit TRPL activity. Releasing caged InsP3 invariably released Ca2+ from internal stores but had only a minor influence on TRPL activity and none at all when Ca2+ release was buffered with BAPTA. Caged InsP3 also failed to activate any light-sensitive channels in situ in Drosophila photoreceptors. Two phospholipase C inhibitors (U-73122 4 microM and bromo-phenacyl bromide 50 microM) reduced both spontaneous and agonist-induced TRPL activity in S2 cells. The results suggest that, as in situ, TRPL activation involves G-protein and PLC; that Ca2+ can both facilitate and in some cases inhibit TRPL channels, but that neither Ca2+ nor InsP3 is the primary activator of the channel.

• Authors: R C Hardie, P Raghu
• Journal: Cell calcium (Cell Calcium) Vol. 24 Issue 3 Pg. 153-63 (Sep 1998) ISSN: 0143-4160 [Print] SCOTLAND
• PMID: 9883270 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Calmodulin-Binding Proteins
• Chelating Agents
• Drosophila Proteins
• Enzyme Inhibitors
• Membrane Proteins
• Recombinant Proteins
• Transient Receptor Potential Channels
• trpl protein, Drosophila
• Egtazic Acid
• Inositol 1,4,5-Trisphosphate
• Carbachol
• Type C Phospholipases
• 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
• Calcium

Topics

• Animals
• Calcium (metabolism)
• Calcium Signaling
• Calmodulin-Binding Proteins (drug effects, genetics, metabolism)
• Carbachol (pharmacology)
• Chelating Agents (pharmacology)
• Drosophila (genetics)
• Drosophila Proteins
• Egtazic Acid (analogs & derivatives, pharmacology)
• Electrophysiology
• Enzyme Inhibitors (pharmacology)
• Inositol 1,4,5-Trisphosphate (metabolism)
• Membrane Proteins (drug effects, genetics, metabolism)
• Recombinant Proteins (genetics, metabolism)
• Transient Receptor Potential Channels
• Type C Phospholipases (antagonists & inhibitors, metabolism)