Voltage-dependent calcium channels

Area of Science:

• Molecular and Cellular Neuroscience
• Ion Channel Physiology
• Pharmacology

Background:

• Voltage-activated calcium channels are crucial for cellular excitability and are classified into low-voltage-activated (LVA) and high-voltage-activated (HVA) subgroups.
• Auxiliary subunits, specifically alpha2delta and gamma families, significantly influence the biophysical properties and function of HVA calcium channels.

Purpose of the Study:

• To clone and characterize novel alpha2delta and gamma auxiliary subunits of voltage-activated calcium channels.
• To investigate the regulatory roles of these subunits on different calcium channel classes.
• To map interaction sites and elucidate the inhibition mechanisms of dihydropyridine (DHP) channel blockers on Ca(v)1.2 channels.

Main Methods:

• Molecular cloning and characterization of new alpha2delta and gamma subunits.
• Electrophysiological recordings to assess the modulation of calcium channel activity by auxiliary subunits.
• Site-directed mutagenesis and functional assays to determine the interaction sites and mechanisms of DHP blockers.
• Pharmacological profiling of the murine neuronal LVA Ca(v)3.1 channel using various organic and inorganic blockers.

Main Results:

• Two novel alpha2delta subunits (alpha2delta-2, alpha2delta-3) and four gamma subunits (gamma-2, gamma-3, gamma-4, gamma-5) were characterized, showing differential regulation of HVA and LVA calcium channels.
• alpha2delta-2 broadly modulates neuronal and non-neuronal channels, while alpha2delta-3 preferentially regulates Ca(v)2.3 channels; gamma subunits exhibit specific interactions with Ca(v)1.2, Ca(v)2.1, and Ca(v)3.1 channels.
• Dihydropyridine blockers interact with inactivated and open states of Ca(v)1.2 channels, with specific amino acid residues in IVS6, IS6, IIIS5, and IIIS6 segments mediating high- and low-affinity inhibition.
• The cloned murine neuronal LVA Ca(v)3.1 channel displays distinct sensitivities to various blockers and unique inactivation kinetics, with determinants located in the intracellular carboxy terminus.

Conclusions:

• Novel alpha2delta and gamma subunits play critical roles in diversifying the function of voltage-activated calcium channels.
• Understanding the interaction sites of DHP blockers provides insights into the structural basis of channel modulation and drug action.
• The characterization of the LVA Ca(v)3.1 channel and its inactivation mechanisms contributes to a deeper understanding of neuronal excitability.