The invention provides isolated nucleic acid and amino acid sequences of
hHAC3, antibodies to hHAC3, methods of detecting hHAC3, and methods of
screening for modulators hyperpolarization-activated cation channels
using biologically active hHAC3. The invention further provides, in a
computer system, a method of screening for mutations of human HAC3 genes
as well as a method for identifying a three-dimensional structure of
human HAC3 polypeptides.