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Articles in PresS, published online ahead of print August 29, 2002
Am J Physiol Heart Circ Physiol, 10.1152/ajpheart.00392.2002
Submitted on May 6, 2002
Accepted on August 23, 2002
1 Biophysics and Physiology, SUNY Buffalo, Buffalo, NY, USA; Department of Cardiology, Wuhan University, Wuhan, Hubei, China
2 Biophysics and Physiology, SUNY Buffalo, Buffalo, NY, USA
* To whom correspondence should be addressed. E-mail: rr32{at}acsu.buffalo.edu.
Kv1.4 encodes a slowly-recovering Ito which inactivates by a fast N-type (intracellular ball and chain) mechanism but has slow recovery due to C-type inactivation. C-type inactivation of the N-terminal deletion mutant (fKv1.4
N) was inhibited by 98 mM [K+]o whereas N-type was unaffected. In 98 mM [K+]o, removal of [K+]i speeded C-type inactivation but had no effect on N-type inactivation, suggesting that C-type inactivation is sensitive to K+ binding to intracellular sites. C-type inactivation is thought to involve closure of the extracellular pore mouth. However, a valine to alanine mutation on the intracellular side of S6 (V561A) of fKv1.4N alters recovery and results in anomalous speeding of C-type inactivation with increasing [K+]o. pHo modulated both N- and C-type inactivation through an S5-H5 linker histidine (H508) with acidosis speeding both N- and C-type inactivation. Mutation of an extracellular lysine to a tyrosine (K532Y) slowed C-type inactivation and inhibited the pH dependence of both N- and C-type inactivation. These results suggest that mutations, [K+] and pH modulate inactivation through membrane-spanning mechanisms involving S6.
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