Cumulative inactivation and the pore domain in the Kv1 channels

AKv1.1a is an Aplysia Kv1 channel close to a mammalian Kv1.4. Both channels show a prominent frequency-dependent cumulative inactivation. The cumulative inactivation of AKv1.1a but not of rKv1.4 was enhanced by the patch excision. To gain structural information about the phenomenon, we examined chimeras of AKv1.1a and rKv1.4. Chimeras with the AKv1.1a pore domain displayed enhanced cumulative inactivation after patch excision. In the pore domain, eight amino acids are different between the two channels. We, therefore, constructed eight mutants of AKv1.1a (A378E, D379P, Q380T, K384Q, R406K, G409T, W411G, L414I) based on the sequence differences. All the mutants showed a similar macroscopic current decay, suggesting that N-type inactivation was not affected. The patch excision failed to enhance the cumulative inactivation in A378E, D379P, G409T, and L414I. P/C-type inactivation in N-terminal deletion mutants (Delta N) became slower in A378E, D379P, G409T and L414I. Internal application of the N-terminal peptide from the ShB channel induces a frequency-dependent block of Delta N-AKv1.1a. By contrast, the block was not frequency dependent in Delta N-A378E, Delta N-D379P and Delta N-G409T. The results suggest that the positions 378, 379, 409, and perhaps 414 in the AKv1.1a backbone are involved in the stability of P/C-type inactivation and the cumulative inactivation of Kv1 channels.