DELETION OF THE N-TERMINUS OF A K-TERM MODULATION BY CAMP AND BETA-1-ADRENERGIC RECEPTOR ACTIVATION( CHANNEL BRINGS ABOUT SHORT)

On deletion of the N-terminus of RCK1 K+ channel, acute modulation of the channel by cAMP-elevating treatments is revealed. This modulation is studied in Xenopus oocytes using two-electrode voltage-clamp, site- directed mutagenesis, and SDS-PAGE analyses. Treatments by Sp-8-Br-cAM PS, a membrane-permeant cAMP analog, and by isoproterenol, a beta 1-ad renergic receptor (beta 1R) agonist, both increased the current amplit udes with no effect on the voltage dependency of activation. The effec t of isoproterenol was blocked by coexpression of either G(alpha S) or G(alpha i3) proteins. The channel protein is phosphorylated on the SP -8-Br-cAMPS treatment at Ser446; however, a phosphorylation-deficient variant in which this site has been altered is still modulated by Sp-8 -Br-cAMPS and isoproterenol. Expression of the full-length channel wit h Kv beta 1.1 auxiliary subunit renders the channel at the same modula tion as that of the truncated one. Taken together, the RCK1 channel ca n be acutely modulated by cAMP and beta 1R activation possibly through protein kinase A (PKA) activation, but not through direct channel pho sphorylation; the involvement of the N-terminus in this modulation is discussed.