Role of Repeat I in the fast inactivation kinetics of the Ca_v2.3 channel

摘要

The molecular basis for inactivation in Ca_v2.3 (α1E) channels was studied after expression of α1E/α1C (Ca_v2.3/Ca_v1.2) chimeras in Xenopus oocytes. In the presence of 10 mM Ba~(2+), the CEEE chimera (Repeat I+part of the I-II linker from Ca_v1.2) displayed inactivation properties similar to Ca_v1.2 despite being more than 90% homologous to Ca_v2.3. The transmembrane segments of Repeat I did not appear to be crucial as inactivation of EC(IS1-6)EEE was not significantly different than Ca_v2.3. In contrast, EC(AID)EEE, with the β-subunit binding domain from Ca_v1.2, tended to behave like Ca_v1.2 in terms of inactivation kinetics and voltage dependence. A detailed kinetic analysis revealed nonetheless that CEEE and EC(AID)EEE retained the fast inactivation time constant (τ_(fast) ≈ 20-30 ms) that is a distinctive feature of Ca_v2.3. Altogether, these data suggest that the region surrounding the AID binding site plays a pivotal albeit not exclusive role in determining the inactivation properties of Ca_v2.3.