CACNA1I (also known as Cav3.3; KIAA1120) encodes Cav3.3, a T type LVA calcium channel found in neurons which is also know as a1I. Voltage-dependent calcium channels control the rapid entry of Ca(2+) into a variety of cell types and are therefore involved in both electrical and cellular signaling. T-type channels, such as CACNA1I, are activated by small membrane depolarizations and can generate burst firing and pacemaker activity
Cacna1i : calcium channel, voltage-dependent, T type, alpha 1I subunit
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CaV 3.2 current
(IC50 , 0.8 μM) is significantly more sensitive to Zn2 + than are CaV 3.1 and CaV 3.3 currents (IC50 ,
80 μM and ∼160 μM, respectively). This inhibition of CaV 3 currents is associated with a shift
to more negative membrane potentials of both steady-state inactivation for CaV 3.1, CaV 3.2 and
CaV 3.3 and steady-state activation for CaV 3.1 and CaV 3.3 currents. We also document changes
in kinetics, especially a significant slowing of the inactivation kinetics for CaV 3.1 and CaV 3.3,
but not for CaV 3.2 currents. (Traboulsie )
PMA augmented the current amplitudes of the three T-type channel isoforms (Cav3.1, Cav3.2, Cav3.3), but
the fold stimulations and time courses differed. (Park )
T-type Ca2+ currents are central determinants of neuronal
excitability that are present in the somatodendritic
compartment of many types of neurones (Carbone & Lux,
1984 ; Talley et al. 1999 ).
Genetic and pharmacological
inhibition of T-type Ca2+ currents has demonstrated the
importance of these currents in various sensory systems,
ranging from pain perception and hyperalgesia (Kim et al.
2003 ; Ikeda et al. 2003 ), mechanoreceptor function (Shin et al. 2003 ) and to olfaction (Kawai & Miyachi, 2001 ).
T-type channels are distinguished from high voltage-activated (HVA)1 Ca2+ channels by their unique biophysical properties, including low voltage activation, fast activation and inactivation kinetics that produce a criss-crossing pattern
between successive traces of a current-voltage (IV) protocol,
slow deactivation kinetics, and tiny single channel conductance (Perez-Reyes , Armstrong , Carbone , Randall ).
Expression studies found that Cav3.3 channels generate currents with much slower activation and inactivation kinetics
than Cav3.1 and Cav3.2 channels, which show the more typical transient kinetics described for native T-type channels (Perez-Reyes , Perez-Reyes , Cribbs , Lee ).
Cav3.1 and Cav3.2 channels are activating and inactivating much faster than Cav3.3 channels. (Park )
The kinetics of
T-type channels resemble those of Na+ channels, albeit on a
slower time scale, suggesting that they may also inactivate by
a ball-and-chain mechanism. However, preliminary evidence
indicates that T-type channels inactivate by similar processes
as HVA Ca2+ channels.Multiple structural elements contribute to the slow kinetics of Cav3.3 channels. (Park )