Dynamic Cell referencing in range function for vba in excel

Hi All,
I am just presenting the vba code below for sorting all columns (A4:T379) based on a value in a single column (M)

Selection.AutoFilter Field:=rownumber, Criteria1:="<01-Feb-2011", Operator:=xlAnd
    Range("A4:T379").Sort Key1:=Range(M3), Order1:=xlAscending, Header:= _
        xlGuess, OrderCustom:=1, MatchCase:=False, Orientation:=xlTopToBottom, _
        DataOption1:=xlSortNormal

The above code sorts the range from A4 to T379 which is nothing but the data below the column headings which has autofilter in it.

My question:
Is it possible to substitute A4 and T379 with two variables which contains the address of the first cell and the last cell in the range. If so, Can anyone provide me with a syntax to substitute variables for A4 and T379 in the range function.

Adv. Thanks for the help.
KK