Hi Ge,

The traces you arr referring to in Panel B, are the current responses of the membrane to changes in the membrane potential. Holding potential of the cell is -80mV, then the researchers are applying gradual depolarizing steps at 10 mV amplitude and 3 second duration, reaching a maximum stimulation at +70mV level. Following these depolarizing pulses, they are holding the membrane potential at -50 mV for 4 second to see the tail currents activated by the brief depolarization. Subsequently the membrane potential returns to the holding potential of -80 mV. Then the amplitude of hERG currents for normoxic and hypoxic conditions over time (hours) are plotted in the lower graph. This is showing that the amplitude of hERG currents are significantly inhibited under hypoxic conditions.

best wishes,

Refik

The concept of current-voltage (I-V) relationship is one first thing that any electrophysiologist learns. Refik explained the data nicely. the authors of the paper you showed did more than most electrophysiologists do which is to draw the exact voltage protocol they used (see inset in B above hypoxic conditions at 24h traces) to generate the family of corresponding recorded currents. Graph B also has the scale bars to give you the exact time of how long they held their membrane voltage to any of the voltages tested. I did not read the paper, but for some reason the I-V relationship was not generated from the recorded traces nor the inactivation-Voltage relationship. Those measurement, if generated, would give more info on how hypoxic conditions affect the channel's characteristics. All I see is a time-course (TC) of the hypoxic condition (which, of course, is important) with time after 6, 12, 18 and 24 hours. I guess, all I want to say is that for a beginner in Ephys., you don't need such a protocol to generate that time-course. You could do the same just by depolarizing the membrane to one voltage followed by another one to see the tail current. To learn more, I recommend that you read two essential books: The first one by the late Areles Molleman - Patch Clamping, An introductory Guide to Patch Clamp Electrophysiology and of course, the second book (the Ephys. Bible) by Bertil Hille - Ion Channels Excitable Membranes. The first book is free to download from the web. Happy reading :)

Welcome, Ge Chang, to the wonderful and sometimes hard world of Electrophysiology. Refik and Fouad gave you good answers. I agree with Fouad: Herg IV curves in normoxia and hypoxia would have provided more information. Likely, they are plotting only the current peak amplitude of the tail current at +70mV. By all means, read the Hill Book! And if you can get your hands on one of the Axon Instruments old manuals, they contain information that you may find useful.

I agree with Jose. To become a decent electrophysiologist takes several years of learning concepts (basic electricity and biophysics). The axon guide is a good start (here :https://www.moleculardevices.com/en/assets/user-guide/dd/cns/axon-guide-to-electrophysiology-and-biophysics-laboratory-techniques). Then you have to take classes somewhere. You may find some good MOOC.

But you have to learn over and over. Cellular electrophysiology is not a simple technique, it is a discipline with many pitfalls.

Best

Fabien