Regulation of a family of inwardly rectifying potassium channels (Kir2) by the m1 muscarinic receptor and the small GTPase Rho
Inwardly rectifying potassium channels Kir2.1–Kir2.3 are important regulators of membrane potential and, thus, control cellular excitability. However, little is known about the regulation of these channels. Therefore, we studied the mechanisms mediating the regulation of Kir2.1–Kir2.3 by the G-protein-coupled m1 muscarinic receptor using the whole-cell patch-clamp technique and recombinant expression in the tsA201 mammalian cell line. Stimulation of the m1 muscarinic receptor inhibited all subtypes of inward rectifier tested, Kir2.1–Kir2.3. The inhibition of each channel subtype was reversible and was attenuated by the muscarinic receptor antagonist, atropine. The protein kinase C activator phorbol 12-myristate 13-acetate (PMA) mimicked the effects of m1 receptor activation by inhibiting Kir2.1 currents. However, PMA had no effect on Kir2.2 or Kir2.3. Inclusion of 200-μM guanosine 5′-O-(2-thiodiphosphate) (GDPβS) in the patch pipette solution prevented the effects of m1 muscarinic receptor stimulation on all three of the channel subtypes tested, confirming the mediation of the responses by G-proteins. Cotransfection with the activated mutant of the small GTPase Rho reduced current density, while C3 exoenzyme, a selective inhibitor of Rho, attenuated the m1 muscarinic receptor-induced inhibition of Kir2.1–Kir2.3. Also, buffering the intracellular calcium concentration with a high concentration of EGTA abolished the m1 receptor-induced inhibition of Kir2.1–Kir2.3, implicating a role for calcium in these responses. These results indicate that all three of the Kir2 channels are similarly inhibited by m1 muscarinic receptor stimulation through calcium-dependent activation of the small GTPase Rho.
KeywordsInward rectifier Muscarinic receptor Small GTPase Rho Signal transduction Kir2.1 Kir2.2 Kir2.3
The authors thank Drs. Y. Kubo and L.Y. Jan for the kind gift of mKir2.1 cDNA, Dr. W. Tang for the kind gifts of hKir2.1 and hKir2.2 cDNAs, Dr. Y. Kurachi for the kind gifts mKir2.2 and mKir2.3 cDNAs, Dr. J.S. Gutkind for the Rho mutants, and Dr. Treisman for the EFC3 plasmid. This work was funded in part by National Institutes of Health grant NS29634 and by the National Science Foundation Office of Experimental Program to Stimulate Competitive Research (NSF EPSCor).
- 4.Chen C, Okayama H (1987) High efficiency transformation of mammalian cells by plasmid DNA. Mol Cell Biol 8:2745–2752Google Scholar
- 25.Karle CA, Zitron E, Zhang W, Wendt-Nordahl G, Kathofer S, Thomas D, Gut B, Scholz E, Vahl C-F, Katus HA, Kiehn J (2002) Human cardiac inwardly-rectifying K± channel Kir2.1b is inhibited by direct protein kinase C-dependent regulation in human isolated cardiomyocytes and in an expression system. Circulation 106:1493–1499CrossRefPubMedGoogle Scholar
- 42.Takahashi N, Morishige K-I, Jahangir A, Yamada M, Findlay I, Koyama H, Kurachi Y (1994) Molecular cloning and functional expression of cDNA encoding a second class of inward rectifier potassium channels in the mouse brain. J Biol Chem 37:23274–23279Google Scholar