I am reading a journal paper about the cell adhesion molecule NCAM2 and I have come across the following statement:
To confirm the functionality of the reporters, neurons were time-lapse recorded before and after application of 90mM K+ used to depolarize membranes and induce Ca2+ influx via VDCCs.
I know that depolarisation is when the membrane potential of a neuron becomes more positive. I have read that the opening of channels that let positive ions flow into the cell causes depolarisation, such as the opening of channels that let Na+ into the cell.
However, the above statement in the paper seems to imply that extracellular K+ ions can also cause membrane depolarisation. I am not sure what the relationship between potassium ions and membrane depolarisation is and I have not found anything about it online. Any insights are appreciated.