Kinetics Of Open- And Closed-state Inactivation Of Kv1.5 At Low pH Or With Ni2+ Ions

Abstract

Previous studies have shown that Ni2+o and H+o inhibit Kv1.5 current by enhancing open state inactivation (OSI) and promoting closed state inactivation (CSI). By combining fast changes of [H+] or [Ni2+] with test depolarizations, the kinetics of OSI and CSI were studied to assess the possible kinship of closed-inactivated and open-inactivated states. At −80 mV, the mean onset time constant of CSI (τCSI) in nominally K+ -free medium was 3.1, 1.2 and 0.18 s at pH 6.9, 6.4 and 5.4, respectively; τOSI, measured at 50 mV, and at the same pHs, was 1.2, 0.6 and 0.16 s. With 0.1 mM Ni2+, τCSI and τOSI were 7.5 s and 1.8 s; in 10 mM Ni2+ these values decreased to 0.6 and 0.4 s, respectively. Following CSI or OSI, either at pH 5.4 or in 0.1 mM Ni2+, recovery in control solution (pH 7.4, Ni2+-free) was biphasic, and the recovery time constants were comparable to those fitted to recovery following OSI in control solution. However, the relative weight of the fast and slow components depended on the ligand used. Following OSI and CSI induced at low pHo, recovery was dominated by the faster process (τ approx. 1s); with Ni2+, recovery occurred mainly by the slower process (τ approx.10 s). Thus, Ni2+ and H+ cause a concentration-dependent increase of CSI and OSI, with τCSI approaching τOSI at high concentrations. Inactivation at low pHo, either from the open- or the closed state, is to a state that is also visited at pH 7.4 and from which recovery is relatively rapid. The latter conclusion also applies for Ni2+, except that the inactivated state is predominantly that from which recovery is slow.