The field includes the biological arts, such as cytometry, and particularly concerns processes, systems, and instruments for automatically measuring action potentials, calcium transients and ionic flux in excitable cells of humans and animals.
Excitable cells are those cells that are able to produce and respond to electrical signals and include neurons, muscle (skeletal, smooth, and cardiac muscle), and secretory cells. Like all cells, excitable cells maintain a resting membrane potential by controlling the levels of certain ions within the cell in relation to the external concentration of those same ions, establishing an electrochemical gradient across the membrane. However, certain stimuli can open specialized sodium channels (e.g., electrical stimuli, mechanical stimuli, or ligand binding) on the membrane of excitable cells that cause an increase in voltage from a negative hyperpolarized level across the membrane toward depolarization of the membrane. Once this membrane depolarization reaches a threshold level, voltage gated sodium channels open causing a rapid depolarization of the cell membrane followed by repolarization, which is referred to as an action potential. Action potentials can propagate along neurons for long distances and cause action potentials to occur in other excitable cells leading to various effects. For example action potentials in muscle cells lead to the rapid release of calcium from intracellular stores resulting in contraction of the cell.
Many fluorescent dyes which respond to changes in membrane voltage and ion concentrations (including but not limited to sodium, potassium, calcium, and chloride ions) are currently known. Using these dyes, researchers can make video recordings of a magnified field of view to observe changes in the intensity of the dyes when loaded into cells. Changes in the intensity of these dyes correlates to the activity of the action potentials (voltage sensitive dyes), calcium transients (intracellular calcium dyes), or ion flux across a membrane (e.g. sodium or potassium dyes). Cytometric analysis of video recordings of cells loaded with these dyes, which measures the change in the intensity of these dyes over time, can provide a quantitative assessment of the kinetics of the action potential, calcium transient or ion flux on a cell by cell basis. Chemical compounds, biological molecules (including but not limited to proteins, DNA and DNA constructs, RNAs, small non-translated RNAs such as siRNA, miRNA, or equivalent, or other molecules derived from biological material), electrical stimulation, or genetic manipulation can be applied to the cells prior to or during the recording. Using cytometric analysis methods the effect the compound, biological molecule, electrical stimulus or genetic manipulation has on the action potential, calcium transient, or ionic flux of the cell can be assessed quantitatively.