Significance of string of histidines in membrane protein?

[Tony Zador]

A newly cloned K channel w/>70% homology to other K channels has a
string of ~10 histidines on the cytoplasmic side, and elsewhere a
string of 6 again on the cytoplasmic side. 

Can anyone suggest any significance to this sequence? What proteins
other than histones have a similar arrangement?

Thanks,
Tony Zador