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-cAMPS, a membrane-permeant cAMP analog, and by isoproterenol, a beta 1-adrenergic receptor (beta 1R) agonist, both increased the current amplitudes with no effect on the voltage dependency of activation. The effect 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 with Kv beta 1.1 auxiliary subunit renders the channel at the same modulation as that of the truncated one. Taken together, the RCK1 channel can be acutely modulated by cAMP and beta 1R activation possibly through protein kinase A (PKA) activation, but not through direct channel phosphorylation; the involvement of the N-terminus in this modulation is discussed.