There are a few approaches that you can take to measure action potential in response to GFP intensity. The first would be to use a high-speed camera, if you have access to one. If not, then you can use a specialized fluorescent microscope, such as a confocal microscope, to image the GFP signal at high speed (up to several thousand frames per second). You can then use software to measure the intensity of the GFP signal over time, and compare it to the action potentials generated. Another approach would be to build a custom microscope setup using a very fast shuttering mechanism (such as an acousto-optic modulator) to rapidly capture images of the GFP signal at different time points. You can then measure the intensity of the GFP signal in each image, and compare it to the action potentials generated. Whichever approach you choose, it is important to ensure that you are using the highest-quality optics and imaging equipment available to you, as this will greatly improve the accuracy of your measurements.

Bandla Ramesh

Does this ( then you can use a specialized fluorescent microscope, such as a confocal microscope, to image the GFP signal at high speed (up to several thousand frames per second).) mean I have to have a high-speed camera?

As far as the confocal option is concerned, you have to consider the required time resolution and compare it to what is achievable with the microscope. The length of an action potential is on the order of milliseconds. The typical dwell time of a scanning confocal microscope (duration of time for acquiring a single pixel) is 10 usec, so even if you record a quite small image of 100x100 pixels, the frame time is 10 usec x 10000 = 0.1 sec. So most likely too slow for recording an action potential. However, if you perform line scanning and record a line of 100 pixels, the "line time" will be 1 msec. If you can decrease the dwell time and the number of pixels further, you can achieve sub-millisec resolution.

You can acquire full frames at a much higher speed with spinning disk confocal microscopes, but I'm not sure you can achieve thousands of frames per second very easily (although never tried personally).

Peter