Patent ID: 7550257

Claim:
A process, said process comprising a) providing, in a suitable container, cells that express a hyperpolarization-activated cation channel; b) hyperpolarizing the cells in the presence of a potential-sensitive fluorescent dye and an isoosmolar sodium-ion-free buffer; c) optionally, determining the membrane potential of the cells; d) incubating the cells with a sample containing at least one substance to be tested for its ability to modulate the activity of the cation channel; e) optionally, determining the membrane potential of the cells; f) optionally, determining whether the membrane potential changed upon addition of the substance(s) to be tested; g) adding sodium ions; h) determining the membrane potential of the cells; i) determining whether the membrane potential changed upon addition of the sodium ions; and j) optionally, recording the change in membrane potential, wherein a change in membrane potential between the time before the sodium ions are added and after the sodium ions are added indicates the presence of at least one substance in the sample that modulates the activity of the cation channel.