How strong of an electric field is dangerous to adult humans?
Research published by WSU Professor Emeritus of Biochemistry and Basic Medical Sciences, Dr. Martin Pall, bears directly on your question about potassium channels.

https://www.researchgate.net/project/microwave-frequency-radiation-acts-via-voltage-gated-calcium-channel-activation

He has concluded that weak EMFs cause cascading health impacts that derive from false electrical signaling of voltage-gated ion channels, and that these impacts include heart disease and the dreaded social bugbear elctrosensitivity (microwave disease).