There is a small amount of biasing current at point a. I have been point a. I felt it. It taught me a lot about electrical safety.
The effect is similar to a hydraulic line that is unpressurized but entirely full of oil. When you open the valve to connect it to a 2000psi source, the oil compresses very, very slightly, and there is this momentary "blip" of flow at a. It then balances out and flow stops.
Essentially it is placing an electrostatic charge on the wire past a. That can be measured or calculated, but it is inconsequential unless the physical material past a is quite large, or the voltage is quite high. I can tell you biasing a 20,000 square foot metal roof, to 600V, is noticeable.
You can think of it as a small capacitor.
AC is a different deal. That tiny biasing current will flow every half cycle, or rather, almost all the time as it changes the electrostatic charge.