Question

1. a) You are doing a patch-clamp recording experiment in which you expose a patch of cell membrane to a small molecule. If the ion channels in the patch of membrane are ligand-gated and the small molecules binds to them, what result would you expect?

b) You are doing a patch-clamp recording experiment in which you expose a patch of cell membrane to a small molecule. If the ion channels in the patch of membrane are ligand-gated and the small molecules do not bind to them, what result would you expect?

c) In a patch-clamp recording experiment, the movement of ions across the membrane is measured as ___.

d) You are doing a patch-clamp recording experiment in which you expose a patch of cell membrane to a small molecule. If the ion channels in the patch of membrane are voltage-gated ion channels, what result would you expect?

Answer 1

Patch referes to a small piece of cell membrane and clamp has an electro-technical connotation. Patch-clamp means imposing on a membrane patch a defined voltage with the purpose to measure a resulting current for the calculation of patch conductance. Clamping could also mean forcing a defined current through a membrane patch. The introduction of patch clamping is done by Neher and sakmann in 1976. In this method, neurologists place a polished glass micropipette against a cell and apply suction to form a high resistance seal. This process isolates a small patch of membrane that contain one or more ion channel. Using Electrode within the micropipette, researchers can clamp or control the electrical properties of the membrane, which is important for analysis of channel activity. The electrode also allows for changes in the voltage across the membrane or the flow of ion through the membrane to be recorded.

a) In first experiment, if we are doing a patch-clamp recording experiment in which we expose a patch of membrane to a small molecule. If the ion channels in the patch of membrane are ligand-gated and the small molecules binds to them. It forms a gigaseal, while that cell membrane remains intact. This allows the recording of currents through single or a few ion channels contained in the patch of membrane captured by the pipette. For ligand-gated channels that are modulated by metabotropic receptors. By only attaching to the exterior of the cell membrane there is very little disturbance of the cell structure. Also, by not disrupting the interior of the cell, any intracellular mechanisms normally influencing the channel will still be able to function as they would physiologically. Using this experiment it is also relatively easy to obtain the right concentration, and once obtained it is fairly stable.

b) In next experiment if we are doing a patch-clamp recording experiment in which we expose a cell membrane to a small molecule. If the ion channels in the patch of the membrane are ligand-gated and the small molecules do not bind them the result will be inside out. A patch of the membrane is attached to the pipette, but detached from the cell and the cytosolic surface of the membrane is exposed to the external media, or bath. One advantage of this experiment is that the experimenter has access to the intracellular surface of the membrane via the bath and can change the chemical composition of what the surface of the membrane is exposed to. This is useful when we want to manipulate the environment at intacellular surface like channels that are activated by intracellular ligands can then be studied through a range of ligand concentrations.

c) In patch-clamp recording experiment, the movement of ions across the membrane is measured as voltage clamp by flow of ions through the membrane. It measures in mV (millivolt).

d) In next experiment, if we are doing a patch-clamp recording experiment in which we expose a patch of cell membrane to a small molecule. If the ion channels in the patch of membrane are voltage-gated ion channels the result will be to measure the ion currents through the membranes of excitable cells, such a neurons, while holding the membrane voltage at a set level. A basic voltage clamp will intaractively measure the membrane potential, then change the membrane potential( voltage) to desired value by adding necessary current. Cell membranes of excitable cells contain many different kinds of channels, some of which are voltage gated. The voltage gated clamp allows the membrane voltage to be manipulated independently of the ionic currents, allowing the current-voltage relationships of membrane channels to be studied.