I agree with the earlier responses and believe that sonication of your sample will be a good help. also add protease inhibitors to avoid proteolysis of your protein during lysis. In addition to cell lysis, sonication  also helps in fragmenting the DNA which makes samples very viscous and if they still remain so, you can add DNAse. And, are you sure about the localization of your protein. Incase, its bound to membrane, you wont be able to detect it in the soluble fraction. If possible, I will also like to have a positive control for the primary antibody. 

I have had gradient gels run like this too.  One thing you want to do is to make sure you very thoroughly wash out the wells with buffer before loading your sample.  Precast gels tend to have excess buffer/gel whatever in the wells that can mess up your sample.  Otherwise, for large proteins you want to run the gel slow (100V) for a long time (2+hrs).  Also make sure you extend your transfer times.  Very viscose samples will also smear in the gel like this.  You can sonicate your sample to reduce the viscosity or change lysis buffers. 

I also think that you are running out of sds when you prepare the sample for electrophoresis, either increase the amount of sds or reduce the amount of sample. 

you may also consider re-sonicating your samples before loading them and reduce the time of exposure during imaging.

I agree with the earlier responses and believe that sonication of your sample will be a good help. also add protease inhibitors to avoid proteolysis of your protein during lysis. In addition to cell lysis, sonication  also helps in fragmenting the DNA which makes samples very viscous and if they still remain so, you can add DNAse. And, are you sure about the localization of your protein. Incase, its bound to membrane, you wont be able to detect it in the soluble fraction. If possible, I will also like to have a positive control for the primary antibody. 

Sergio,

I think you have a lot of issues with your samples and not so much with the gels themselves because you standard looks fairly good.  But what is your standard?  Is there just three proteins?  The really big dark ones?  Or are those other proteins part of you standard?  I run lots of mucin gels and they are difficult to prepare.  First of all always add the same quantities of protein to each lane.  So run you Lowry protein assays and add 10 to 20 ug per lane (depending on how many wells you).  Always try to add the same volume of sample to each lane.  After you have prepared the samples boil them in glass tube (I use durham tubes).  Also I trust you are reducing the samples, 5% beta mercaptoethanolamine is the best in my hands.  Make sure the samples are mixed well before you boil them.  I also always use Hamilton syringes (flat tip 50 or 100 ul sizes) to mix and load the samples.  Let me know how this works out.  Good luck.

Butch