Pacemaker Channels Produce an Instantaneous Current

• Published in: The Journal of biological chemistry Vol. 277; no. 7; pp. 5101 - 5109
• Main Authors: Proenza, Catherine, Angoli, Damiano, Agranovich, Eugene, Macri, Vincenzo, Accili, Eric A
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 15.02.2002
• Subjects: Animals; Cell Membrane - metabolism; Chlorine - metabolism; CHO Cells; Cricetinae; Cyclic AMP - metabolism; Electric Conductivity; Electrophysiology; Green Fluorescent Proteins; Hydrogen-Ion Concentration; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Immunohistochemistry; Ion Channels - chemistry; Ion Channels - physiology; Luminescent Proteins - metabolism; Mice; Microscopy, Confocal; Muscle Proteins; Mutagenesis, Site-Directed; Mutation; Potassium - metabolism; Potassium Channels; Protein Binding; Protein Structure, Tertiary; Recombinant Fusion Proteins - metabolism; Time Factors; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M106974200

Spontaneous rhythmic activity in mammalian heart and brain depends on pacemaker currents (I h ), which are produced by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Here, we report that the mouse HCN2 pacemaker channel isoform also produced a large instantaneous current (I inst(HCN2) ) in addition to the well characterized, slowly activating I h . I inst(HCN2) was specific to expression of HCN2 on the plasma membrane and its amplitude was correlated with that of I h . The two currents had similar reversal potentials, and both were modulated by changes in intracellular Cl − and cAMP. A mutation in the S4 domain of HCN2 (S306Q) decreased I h but did not alter I inst(HCN2) , and instantaneous currents in cells expressing either wild type HCN2 or mutant S306Q channels were insensitive to block by Cs + . Co-expression of HCN2 with the accessory subunit, MiRP1, decreased I h and increased I inst(HCN2) , suggesting a mechanism for modulation of both currents in vivo . These data suggest that expression of HCN channels may be accompanied by a background conductance in native tissues and are consistent with at least two open states of HCN channels: I inst(HCN2) is produced by a Cs + -open state; hyperpolarization produces an additional Cs + -sensitive open state, which results in I h .