what is more important in protein electrophoresis? voltage or current? - sds-page (Apr/11/2008 )

As in the topic title,i have been wondering what is more important for obtaining sharper bands.
In my power supply i can adjust manually the vollts,ampers and watts. In other words adjusting the maximum voltage and the maximum watts i can keep the current at the same level for longer time.
I am interested in 55-40 kDa proteins and as far as the ampers keep lowering during the electrophoresis i came up with this question
what is your opinion?

We use constant voltage, and always get sharp bands, except when the amount of protein gets too big

we always use constant current, but this is because when we started using electrophoresis, the power supply only allowed us to adjust current.

we found it to work as well as any other. so choose your preference.

In reality either V or I should be pretty close. Since in any experimetn you are trying to keep as much the same as possible, the resistance from running buffer, gel, and samples should stay approximately the same. Thus the voltage and current should not change much. That said, I keep the voltage constant and do see a change in current while it is running - not a big change though.

Thank you for your replies.Our power supply can output 300 watts.The first time i used it i just set it to 200 volts.I don't remember the initial ampers,but i remember that the electrophoresis finished with two gels at 41mA, although it had started around 200 or more.I did a couple of more runs but i didn't notice a big difference.The question is a little bit theoretical and i was wondering if big proteins are affected more by voltage and smaller proteins more by current or the reverse.I will try to persuate my supervisor to let me do some runs and see the results by staining with coomasie R250.

As in the topic title,i have been wondering what is more important for obtaining sharper bands.
In my power supply i can adjust manually the vollts,ampers and watts. In other words adjusting the maximum voltage and the maximum watts i can keep the current at the same level for longer time.
I am interested in 55-40 kDa proteins and as far as the ampers keep lowering during the electrophoresis i came up with this question
what is your opinion?

After a lot of thinking i ended up that constant current with 200 volts will do it.I haven't run an empty gel (without samples) to test the current behaviour but the drop in current might be caused by the immobilization of the larger proteins in the gel.Larger proteins carry a bigger amount of charge due to the sds.So stable current may indicate stable protein flow.I recall that i have refilled with fresh running buffer during an electrophoresis and the current didn't change at all,so it doesn't have to do with the ions in the buffer.(although conductivity may decrease).
If i am wright, stable current would lead to better protein separation since smaller proteins would not have to pass through the stuffed by large proteins gel pores.
But all of this is just theory,maybe the use of stacking gel gives the appropriate solution and resolution

I use constant current too. I guess the best way is to check manufacturer's manual. I think they mention about the current and voltage thingy.

I ran an empty gel and the current behaviour was the same
So something in the gel migrates too, creating the current.
There are two questions
a)what is creating the current
b)do we want/need it to migrate along with our samples?
(in case of sds molecules)