You can find the Texboxes and get the data from it.
Try this:
protected void Gridview1_SelectedIndexChanged(object sender, EventArgs e)
{
string s1 = ((TextBox)Gridview1.SelectedRow.FindControl("TextBox1")).Text;
string s2 = ((TextBox)Gridview1.SelectedRow.FindControl("TextBox2")).Text;
string s3 = ((TextBox)Gridview1.SelectedRow.FindControl("TextBox3")).Text;
}
--Amit