Hyperpolarization-activated cation currents, termed I, I, or I, were initially discovered in heart and nerve cells over 20 years ago. These currents contribute to a wide range of physiological functions, including cardiac and neuronal pacemaker activity, the setting of resting potentials, input conductance and length constants, and dendritic integration. The hyperpolarization-activated, cation nonselective (HCN) gene family encodes the channels that underlie I. Here we review the relation between the biophysical properties of recombinant HCN channels and the pattern of HCN mRNA expression with the properties of native I in neurons and cardiac muscle. Moreover, we consider selected examples of the expanding physiological functions of I with a view toward understanding how the properties of HCN channels contribute to these diverse functional roles.

Keyword(s): channelsHCNheartneuronpacemaker

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  • Article Type: Review Article
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