Hello everyone !
I´m doing experiments in current-clamp recordings. Basically I´m trying to stimulate cells expressing an opsin sensitive to blue light to see how they respond to this stimulation (10 ms pulse). Recently, I saw that the protocole by itself without the light (the shutter is closed) induce an artefact (0,2-0,4 mV, 10ms corresponding to the duration of my pulse, cf the picture).
How can I avoid that ?
I´m using pclamp with a Digitizer 1550A and a Muticlamp 700B. The light is given through a cool LED pE-4000.
Thanks for your help !
Hi Noemie,
Two things come to mind to explain that artifact. First, the shutter isn't closing properly, thus letting some light passing into the tissue and activating your opsins. In a dark environment, try measuring if there is any residual light coming out even when the shutter is closed. Second, also unlikely but I've seen this happening, double check that your protocol is not injecting current into the system. See if the artifact remains with I=0. You can also check this by measuring your current using an oscilloscope.
Hope it helps.
Best,
Claudio
It may be crosstalk between channels in the Digitizer, you can (kind of) check that by removing the TTL BNC cable. We see similar artefacts (only difference is NI acquisition), but as long as they are linearly additive, the artefacts can be subtracted. If it is consistent and reproducible, I wouldn't worry about it. In addition, you will also get direct photovoltaic currents when you have the shutter open. Again, if compared insignificant to your measured ionic current, you can just live with it (but of course it is always good to understand everything as much as possible of what's happening, even if you decide to disregard it).