Answering myself: I have seen that there is a table SDE.VERSION_1_ROW_LOCKS. When I make the GetFeatureWithLock call, a record is stored in this table and disappears after timeout.
Deleting this record is enough to unlock the feature locked by GetFeatureWithLock operation or are other SDE tables involved?
Thanks in advance for your help,
Best regards,
Montse
SQL> SELECT * FROM VERSION_1_ROW_LOCKS;
LOCK_ID OC_ID ROW_ID ISSUE_DA EXP_DATE
-------------------------------------- ---------- ---------- -------- --------
{F412B54A-DE16-4BD6-87D6-73F86A2DEB13} 641 5004 14/09/12 14/09/12