1. Patch clamping A. Drexel University College （1。）.pdfVIP

Series Resistance Compensation 1. Patch clamping  Patch clamping is a form of voltage clamping, a technique that uses a feedback circuit to set the membrane potential (Vm) of a cell to a desired command value (Vcom). With membrane potential fixed, the membrane current is measured. The patch clamp amplifier thus must function as a current-to-voltage converter to allow this current to be displayed on an oscilloscope or computer. A. The patch clamp amplifier is a differential amplifier that operates to make the output equal to the difference between the two inputs. V = V – V . o com p B. When a feedback resistor, R , is placed between the output and the negative input of the f amplifier (point 1) a current flows through the feedback resistor to make the voltage at 1 (i.e. V ) equal to that at V . V becomes the “command” for voltage clamping the pipette p com com voltage, Vp . Ohm’s Law states that a current will flow through this resistance proportional to the voltage difference between the two ends of the resistor. I = (V – V ) / R f o p f Rearranging this equation gives: V =I R + V o f f p Since current must be conserved, the current flowing into point 1 must be equal to the pipette current, Ip , which flows out of this point. (We can assume that no current flows into the negative input to the amplifier.) If = - Ip Substituting into the