For more info on voltage clamp technique one may read books, visit labs or check for other web contents. Here are some choices for reading material.

Books:

1. Hodgkin AL, AF Huxley & B Katz (1952) Measurement of current-voltage relations in the membrane of the giant axon of Loligo. J. Physiol. 116, 424-44
2. Kandel, Eric et.al. Principles of Neural Science. New York: McGraw-Hill, 2000.

Webliography:

Voltage clamp techniques

Video Reference:

http://www.youtube.com/watch?v=lf3ZQND_Lxk