Fast inactivation of Shaker K+ channels is highly temperature dependent.
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 degrees C to 5 degrees C: (1) the peak amplitude decreased with the temperature coefficient Q10 equal to 1.51; (2) the activation time constant increased with a Q10 equal to 3.14; (3) the decay time constant increased with a Q10 of 7.20, while the recovery from inactivation was less temperature-dependent (Q10=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 Q10 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.
Nobile
M
M
Istituto di Cibernetica e Biofisica, C.N.R., Genoa, Italy.
Olcese
R
R
Toro
L
L
Stefani
E
E
D000818:Animals; D004330:Drosophila / Q000235:genetics* / Q000378:metabolism*; D004553:Electric Conductivity; D005260:Female; D006706:Homeostasis; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D013696:Temperature; D013997:Time Factors; D014982:Xenopus laevis
D015221:Potassium Channels