C# - Set Variables To Gridview Cells?

I'm relatively new to ASP, so this may be a simple fix that I am just not figuring out (here's hoping!). I am working in VisualStudio2010 using C#.

Basically, I have a table in SQL with the following columns: Product, ProductGroup, Attribute1Value, Attribute2Value, Attribute3Value

For each ProductGroup, the Attribute definition is different. For instance, in ProductGroup1, Attribute1 is Size and Attribute1Value might be 2,3,5, etc. In ProductGroup2, Attribute1 is Quality and the Attribute1Values would be Standard, Economy, Premium, etc.

I will only ever pull in one Product Group at a time and would like to have my column headers reflect the Attribute definition (Header= Size rather than Attribute1Value when applicable".

What I would like to do is pull in a gridview that is invisible with the columns ProductGroup, Attribute1, Attribute2, Attribute3 and then assign the values within the column to be variables that I can use to reassign my column headers. I have been able to set column headers based on other variables (specifically the selected value from a dropdown), but am having trouble with the code to set variables equal to gridview values.

When I tried

protected void Page_Load(object sender, EventArgs e)
{
lblAttribute1.Text = GridView4.Rows[0].Cells[2].Text;
}
protected void RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.Header)
{
e.Row.Cells[3].Text = lblAttribute1.Text;
}
}

I got the error message that my index was out of range. I thought at first that this may be because my Gridviews have no rows upon page load, only after a few selections from DropDowns, but I don't know if they are at all related. Is there a better way to do this in general?