This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concepts in physiology, Subject name: Physiology
Which of the following is used to study current flow across a single channel: 
Select and explain. 
A. Patch clamp, B. Voltage Clamp, C. Iontophoresis, D. Galvanometry
A: Patch clamp
Answer: A: Patch clamp 
Explanation: Patch clamp: measures ionic currents through a single ion channel. It has four configurations: Voltage clamp: whole cell voltage clamp measures currents across cell membranes. In using this apparatus, two electrodes are inseed into the nerve fiber. One of these electrodes is used to measure the voltage of the membrane potential, and the other is used to conduct electrical current into or out of the nerve fiber. Iontophoresis: a technique of introducing ionic medicinal compounds into the body through the skin by applying a local electric current.