Detection of transmembrane potentials by optical methods

A kit comprising in separate vessels:

• a) a coumarin-labeled phospholipid having the formula:
• wherein R is a hydrophobic lipid anchor comprising 14–35 carbons;
• and
• b) a mobile hydrophobic molecule capable of redistributing from a first face of a cellular membrane to a second face of the cellular membrane in response to a change in the membrane potential, and which can undergo energy transfer with the coumarin-labeled phospholipid upon exposure with excitation light by either (i) donating excited state energy to the coumarin-labeled phospholipid, or (ii) accepting excited state energy from the coumarin-labeled phospholipid.

A method of detecting a change in the membrane potential in at least one cell, comprising:

• a) contacting said at least one cell with a mobile hydrophobic molecule, wherein said mobile hydrophobic molecule redistributes from a first face of the membrane to a second face of the membrane in response to said change in the membrane potential, and which undergoes energy transfer with a coumarin-labeled phospholipid upon exposure with excitation light by either (i) donating excited state energy to the coumarin-labeled phospholipid, or (ii) accepting excited state energy from the coumarin-labeled phospholipid, wherein the efficiency of energy transfer between said mobile hydrophobic molecule and said coumarin-labeled phospholipid is dependent on the membrane potential, said coumarin-labeled phospholipid having the formula:
• wherein R is a hydrophobic lipid anchor comprising 14–35 carbons;
• b) contacting said at least one cell with said coumarin-labeled phospholipids,
• c) exposing the membrane to a stimulus thereby altering the membrane potential,
• d) exposing the membrane to excitation light,
• e) determining the degree of energy transfer between the mobile hydrophobic molecule and the coumarin-labeled phospholipid,
• f) relating the degree of energy transfer to the membrane potential thereby detecting a change in the membrane potential.

A method of identifying a test chemical that affects a change in membrane potential in at least one cell comprising the steps of:

• a) contacting said at least one cell with a mobile hydrophobic molecule, wherein said mobile hydrophobic molecule redistributes from a first face of the membrane to a second face of the membrane in response to said change in the membrane potential, and which undergoes energy transfer with a coumarin-labeled phospholipid upon exposure with excitation light by either (i) donating excited state energy to the coumarin-labeled phospholipid, or (ii) accepting excited state energy from the coumarin-labeled phospholipid, wherein the efficiency of energy transfer between said mobile hydrophobic molecule and said coumarin-labeled phospholipid is dependent on the membrane potential, said coumarin-labeled phospholipid having the formula:
• wherein R is a hydrophobic lipid anchor comprising 14–35 carbons;
• b) contacting said at least one cell with said coumarin-labeled phospholipids,
• c) exposing the membrane to said test chemical thereby altering the membrane potential,
• d) exposing the membrane to excitation light,
• e) determining the degree of energy transfer between the mobile hydrophobic molecule and the coumarin-labeled phospholipid,
• f) relating the degree of energy transfer to the membrane potential thereby identifying said test chemical.