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Modulating modulation: crosstalk between regulatory pathways of presynaptic calcium channels
Gerald W Zamponi1, Terrance P Snutch
1Department of Physiology and Biophysics, University of Calgary, Canada. zamponi@ucalgary.ca
Abstract:
The activity of some voltage-gated calcium channels (VGCCs) can be inhibited by specific G protein beta subunits. Conversely, in the case of N-type VGCCs, protein kinase C can relieve Gbeta-dependent inhibition by phosphorylating at least one specific site on the calcium channel. A recent publication describes a newly identified method of intracellular regulation of specific VGCCs. Wu et al. have uncovered that VGCC activity can be regulated by phosphatidylinositol-4',5'-bisphosphate (PIP2). Whereas PIP2 is important for maintaining the activity (open state) of Cav2.1 (N-type) and Cav2.2 (P/Q-type) channels, the enzymatic breakdown of PIP2 leads to the inactivation of these channels. Additionally, PIP2 can cause changes in voltage-dependent activation of Cav2.2 (P/Q-type) channels that make it more difficult for these channels to open (from the closed state). Furthermore, protein kinase A activity can circumvent PIP2-mediated inhibition. Thus, the PIP2-mediated regulation of VGCCs is tightly controlled by the functions of kinases (and phosphatases), as well as phospholipases. Wu et al. stress that because PIP2 can be found at synapses, PIP2-dependent control of VGCCs "could have profound consequences on synaptic transmission and plasticity."
Insights
Phosphatidylinositol-4',5'-bisphosphate (PIP2) regulates voltage-gated calcium channels (VGCCs). PIP2 depletion inactivates Cav2.1 and Cav2.2 channels, impacting synaptic transmission and plasticity.
Area of Science:
- Neuroscience
- Molecular Biology
- Cellular Signaling
Background:
- Voltage-gated calcium channels (VGCCs) are crucial for neuronal function.
- G protein beta subunits and protein kinase C (PKC) are known regulators of VGCCs.
- N-type VGCCs can be inhibited by Gbeta subunits, with PKC relieving this inhibition via phosphorylation.
Purpose of the Study:
- To identify novel intracellular regulatory mechanisms of specific VGCCs.
- To investigate the role of phosphatidylinositol-4",5"-bisphosphate (PIP2) in VGCC regulation.
- To understand how PIP2 levels influence the activity of Cav2.1 and Cav2.2 channels.
Main Methods:
- The study likely involved electrophysiological recordings to assess channel activity.
- Biochemical assays may have been used to determine PIP2 levels and enzymatic activity.
- Molecular biology techniques were probably employed to study channel phosphorylation and interactions.
Main Results:
- Phosphatidylinositol-4",5"-bisphosphate (PIP2) was identified as a key regulator of VGCCs.
- PIP2 maintains the open state of Cav2.1 (N-type) and Cav2.2 (P/Q-type) channels.
- PIP2 breakdown leads to inactivation of these channels and alters voltage-dependent activation.
- Protein kinase A (PKA) can overcome PIP2-mediated inhibition.
Conclusions:
- PIP2-mediated regulation of VGCCs is a significant intracellular control mechanism.
- This regulation is influenced by the interplay of kinases, phosphatases, and phospholipases.
- PIP2-dependent control of VGCCs at synapses may profoundly affect synaptic transmission and plasticity.
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