Do gas discharge tubes used e.g. for surge protection have a polarity, i.e., do they protect in both directions (i.e., depending which wire is hit, or if it is a positive/negative lightnings?
The symbol (see below, from Wikipedia) has a dot that suggests some asymmetry. Electrons should be able to jump in any direction, but how are the positive/negative electrodes engineered to facilitate/stand the discharges?