Voltage-Gated Channels

Outline by Avalon Marker and Shelby Pickett
Voltage Gated Channels

• Na+
• K+
• Ca2+ = Transmitter release.
  • Found on the presynaptic axon terminal
  • Voltage-gated calcium channels (CaVs) are transmembrane proteins activated by depolarization of membrane potential. The calcium that enters through CaVs is crucial for cellular processes including gene expression, hormone release, neurotransmitter release, cardiac muscle contraction, and pacemaker activity.
  • Based on their activation threshold, CaVs are classified as either high or low voltage activated (HVA and LVA).
  • Genes that encode for voltage-gated calcium channels are grouped into three subfamilies, each with their own distinct function:
    • The CaV1 subfamily conducts L-type Ca currents
      • CACNA1S, CACNA1C, CACNA1D, and CACNA1F
    • The CaV2 subfamily conducts N-, P/Q-, and R-type Ca currents
      • CACNA1A, CACNA1B, and CACNA1E
    • The CaV3 subfamily conducts T-type Ca currents
      • CACNA1G, CACNA1H, and CACNA1I
  • L, N, T type currents
    • L-type Ca currents (High-threshold calcium current ICa(L)) initiate excitation-extraction coupling in muscle cells and secretion in endocrine cells, control gene transcription, as well as controlling many enzymes.
    • N-, P/Q-, and R-type Ca currents (ICa(P), ICa(Q), ICa(N), ICa(R)) and the associated CaV2 subfamily are often found concentrated in nerve terminals where Ca influx is required for the release of chemical neurotransmitters; P/Q- and R-types currents are poorly understood.
    • T-type Ca currents (ICa(T)) are activated at negative membrane potentials and are transient; these are modulated by muscarinic acetylcholine receptors. These particular channels are important as they are seen in cells that repetitively fire, such as sinoatrial nodal cells that serve as pacemakers in the heart or neurons in the thalamus that generate sleep rhythms.
    • Synaptic transmission is triggered by opening of mainly N- and P/Q-type calcium channels
  • Pore is formed by the α1 subunit
    • This is similar to the voltage-gated Na+ channel α subunit
    • α2 and δ subunits are associated glycoproteins
    • β subunits are intracellular