Visual Basic.NET - recorrer todas las filas de una columna de un DataGridView

For filas As Integer = 0 To DataGridView1.RowCount - 1

            For Columnas As Integer = 0 To DataGridView1.ColumnCount - 1

                MsgBox(Me.DataGridView1.Item(Columnas, filas).Value)

            Next

Next

For filas As Integer = 0 To DataGridView1.RowCount - 2

    For Columnas As Integer = 0 To DataGridView1.ColumnCount - 2

           My.Computer.Keyboard.SendKeys(TextBox1.Text, True)

    Next

Next