[C#]
//Reworked VirtualGrid sample
//modify this event handler
private object VM_GetNodeCellValue(object sender, NodeBase node, int index)
{
      //check individual cell displaying
      if (node.Index == 3 && index == 2)
        return DateTime.Now.ToLongTimeString();
      //check another cell displaying (shouldn't invaliated)
      if (node.Index == 3 && index == 3)
        return "C" + DateTime.Now.ToLongTimeString();
      Column col = virtualGrid.Columns.FieldMapColumnFromIndex(index);
      return string.Format("Cell[{0}],[{1}]", node.Index, col.Caption);
}

//Add new button and add this Cick event handler
//this handler runs invalidation of node with index =3 in the column with index = 2 each 10 milliseconds
private void button1_Click(object sender, System.EventArgs e)
{
      Timer timer = new Timer();
      timer.Interval = 10;
      timer.Tick += new EventHandler(timer_Tick);
      timer.Start();
}

//timer Tick event handler
private void timer_Tick(object sender, EventArgs e)
{
      virtualGrid.InvalidateCell(virtualGrid.Rows.Items[3], virtualGrid.Columns.Items[2]);
}

[C#]
private void refreshDataBtn_Click(object sender, System.EventArgs e)
{
  // this method refreshes only one cell contents
  Random rnd = new Random();
  NodeBase node = performanceGrid.Rows.Items[3];
  performanceGrid.Columns.Items[0].SetValue(node, rnd.NextDouble().ToString());          
}

[c#]
//1. First way - works fine
node.SetCellValue(0, rnd.NextDouble().ToString());
//----------------------
//2. Second way - works fine
node["Column0"] = rnd.NextDouble().ToString();
//----------------------
//3. Third way - works fine
node[0] = rnd.NextDouble().ToString();
//----------------------
//4. Fourth way - works fine
performanceGrid.Columns.Items[0].SetValue(node, rnd.NextDouble().ToString());
//----------------------