I applied one coat on wooden planks using special paint for wood. Can I use regular paint for the second coat?
It is generally best to stay with whatever base material is used for the first coat. That is, if the "special" paint was oil based, then continue with an oil based paint. Switching to say acrylic or water based will not provide a good bond between paints. 

Can you use it... well you can, but you may need to use several coats and you may find it comes off easily when bumped with the vacuum cleaner etc.