Why is the tightness of the seal used for patch clamp technique denoted as Mega Ohms? Ohms is an unit for resistance then how does it indicate the tightness of the seal between the pipette and the cell? Please let me know. Thanks.
The seal should be in megaohms.
Megaohms mean that the resistance is very high.
This is to prevent the leakage of the current from the seal between the pipette and the cell membrane.
For patch clamping, the seal should be in the Giga Ohm Range; more than 1 GOhm for whole cell recordings and even better for single channel recordings.
The quality of the seal is measured in Ohms because if in patch clamp, the minute area being patched is tightly sealed to the pipette tip, there should be no flow of current across the area of the membrane being patched or through the interface between the pipette tip and the membrane. Because biologcal membranes are not ususally porus to charged ions unless a conduit like a voltage gated or ligand gated ion channel is activated, they have a very high resistance when a potential difference is applied across the membrane.
A well sealed patch will be in the order of Giga ohms because there is little or no flow of ions across the membrane or through the interface between pipette and membrane. Any "Leak" current by the flow of ions into the patch through a bad seal will reduce the resistance because according to Ohms law:
Therefore if the value of I increases because of leak, the Resistance R falls. Therefore we can use resistance as an accurate measure of seal quality in patch clamp.