Fast inactivation of Shaker K+ channels is highly temperature dependent

Abstract

 The energy profile of the interaction between the NH₂-terminal inactivation domain and the internal mouth of the Shaker H4 K⁺ channel has been investigated. Macroscopic currents from channels normally inactivating (Shaker H4) and with the inactivation removed (Shaker H4-IR) were recorded at different temperatures using the cut-open oocyte technique. Changes in temperature had a dramatic effect on the inactivation phase. The following parameters were obtained in Shaker H4, lowering the temperature from 20°C to 5°C: (1) the peak amplitude decreased with the temperature coefficient Q ₁₀ equal to 1.51; (2) the activation time constant increased with a Q ₁₀ equal to 3.14; (3) the decay time constant increased with a Q ₁₀ of 7.20, while the recovery from inactivation was less temperature-dependent (Q ₁₀=1.57) than the installation of the inactivation phase. At 0 mV, the ratio between the steady state level and the peak amplitude of the current increased with a Q ₁₀ of 2.95. These findings indicate that the installation of a fast inactivation process has a strong temperature dependence, while the recovery phase from inactivation is less temperature dependent. These observations support the idea of an NH₂-terminal blocking mechanism for inactivation and flexible conformation of the blocking particle.