reason for curved bands? - (Oct/23/2014 )

I have noticed this with highly concentrated samples - loaded 3-4ul of sample with same volume of sample buffer. The gel pic is attached. Why do the bands curve up in the middle and what can I do to prrevent it? I am guessing diluting the sample might help but open to all suggestions.Thanks!

Probably too much salt in your lysis buffer. Often you will see this also when the BB is approaching the bottom of the gel and hits inconsistencies in the gel/liquid interface, this usually doesn't affect the protein bands, unless you are looking at small proteins

how does the stained gel look (if transferred, how does the ponceau stained membrane look)?