FAST INACTIVATION OF SHAKER K-DEPENDENT( CHANNELS IS HIGHLY TEMPERATURE)

The energy profile of the interaction between the NH2-terminal inactiv ation domain and the internal mouth of the Shaker H4 k(+) channel has been investigated. Macroscopic currents from channels normally inactiv ating (Shaker H4) and with the inactivation removed (Shaker H4-IR) wer e recorded at different temperatures using the cut-open oocyte techniq ue. Changes in temperature had a dramatic effect on the inactivation p hase. The following parameters were obtained in Shaker I-lit, lowering the temperature from 20 degrees C to 5 degrees C: (1) the peak amplit ude 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 tile recovery from inactivation was less temperature-dependent (Q(10)=1.57) than the installation of the inactivation phase. Al 0 mV, the ratio b etween the steady state level and the peak amplitude of the current in creased with a Q(10) of 2.95. These findings indicate that the install ation of a fast inactivation process has a strong temperature dependen ce, while the recovery phase from inactivation is less temperature dep endent. These observations support the idea of an NH2-terminal blockin g mechanism for inactivation and flexible conformation of the blocking particle.