Abstract
The human Kv1.5 potassium channel forms the IKur current in atrial myocytes and is functionally altered by coexpression with Kvbeta subunits. To explore the role of protein kinase A (PKA) phosphorylation in beta-subunit function, we examined the effect of PKA stimulation on Kv1.5 current following coexpression with either Kvbeta1.2 or Kvbeta1.3, both of which coassemble with Kv1.5 and induce fast inactivation. In Xenopus oocytes expressing Kv1.5 and Kvbeta1.3, activation of PKA reduced macroscopic inactivation with an increase in K+ current. Similar results were obtained using HEK 293 cells which lack endogenous K+ channel subunits. These effects did not occur when Kv1.5 was coexpressed with either Kvbeta1.2 or Kvbeta1.3 lacking the amino terminus, suggesting involvement of this region of Kvbeta1.3. Removal of a consensus PKA phosphorylation site on the Kvbeta1.3 NH2 terminus (serine 24), but not alternative sites in either Kvbeta1.3 or Kv1.5, resulted in loss of the functional effects of kinase activation. The effects of phosphorylation appeared to be electrostatic, as replacement of serine 24 with a negatively charged amino acid reduced beta-mediated inactivation, while substitution with a positively charged residue enhanced it. These results indicate that Kvbeta1.3-induced inactivation is reduced by PKA activation, and that phosphorylation of serine 24 in the subunit NH2 terminus is responsible.
Highlights
Voltage-gated Kϩ channels play a critical role in the normal physiology of excitable cells
The effects of phosphorylation appeared to be electrostatic, as replacement of serine 24 with a negatively charged amino acid reduced -mediated inactivation, while substitution with a positively charged residue enhanced it. These results indicate that Kv1.3-induced inactivation is reduced by protein kinase (PKA) activation, and that phosphorylation of serine 24 in the subunit NH2 terminus is responsible
Kϩ currents contribute to action potential repolarization in cardiac cells [1, 2] while in vascular smooth muscle, regulation of membrane potential by Kϩ currents is a major determinant of vascular tone [3, 4]
Summary
Voltage-gated Kϩ channels play a critical role in the normal physiology of excitable cells. Two  subunits cloned from ferret and human heart [13,14,15,16,17], Kv1.2 and Kv1.3, represent splice variants from the same gene These two proteins are identical in the carboxyl 329 amino acids, and this portion appears to be responsible for physical interaction or binding with the ␣ subunit [12, 18]. We found that coexpression of Kv1.3, but not Kv1.2, enabled a response to kinase activation, with marked slowing of fast inactivation and an increase in Kϩ current These effects can be attributed to phosphorylation of a specific consensus site by PKA in the NH2 terminus of the Kv1.3 subunit
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