DataContext db;
        private void Form1_Load(object sender, EventArgs e)
        {
            db = new DataContext();
            bindingSource.DataSource = db.Tables;
            DataGridView.DataSource = bindingSource;            
        }

   
         db.Refresh(System.Data.Linq.RefreshMode.OverwriteCurrentValues,db.tables);
         BindingSource.ResetBindings(false);

void ReadDoc()
 {
 db = new t_1DataContext();
 t_1BindingSource.DataSource = db.t_1s;
}

string s = String.Format("t_1s.Count={0} \n BindingSource.Count ={1}",
                db.t_1s.Count(), t_1BindingSource.Count);
MessageBox.Show(s);

t_1s.Count=  4  
BindingSource.Count =  2 

 db.Dispose();
 ReadDoc();