voltage-dependent Ca+2 channel alpha-1G (T type, Cav3.1c, NBR13, CACNA1G, KIAA1123)

^[1]

Function

pore-forming & voltage-sensitive alpha-1 subunit of voltage-sensitive Ca+2 channel
alpha-1G gives rise to T-type Ca+2 currents.
- T-type Ca+2 channels belong to the low-voltage activated (LVA) group
- strongly blocked by mibefradil
- a particularity of T-type Ca+2 channels is an opening at quite negative potentials & a voltage-dependent inactivation
- T-type channels serve pacemaking functions in both central neurons & cardiac nodal cells & support Ca+2 signaling in secretory cells & vascular smooth muscle
role modulation of firing patterns of neurons during information processing
role in cell growth processes
activated by CaM-kinase II In response to increasing intracellular Ca+2

each of the 4 internal repeats contains 5 hydrophobic transmembrane segments (S1, S2, S3, S5, S6) & one positively charged transmembrane segment (S4)
S4 segments probably represent the voltage-sensor & are characterized by a series of positively charged amino acids at every third position
the linker region between repeat III & IV probably play a role in the inactivation of the channel
the C-terminal part may be implicated in the anchoring of the protein in the membrane, interfering/restricting its lateral diffusion
belongs to the Ca+2 channel alpha-1 subunit (TC 1.A.1.11) family

membrane

named isoforms=14 Additional isoforms seem to exist

highly expressed in brain, including: amygdala, subthalamic nuclei, cerebellum & thalamus
moderate expression in heart
low expression in placenta, kidney & lung
expressed in colon & bone marrow
expressed in tumor cells to a lesser extent
highly expressed in fetal brain
also expressedd in peripheral fetal tissues including heart, kidney & lung, suggesting a developmentally regulated expression