Rota devised by a vital supplier (5)
I believe the answer is:
aorta
'vital supplier' is the definition.
(vital artery)
'rota devised by a' is the wordplay.
'devised' indicates an anagram.
'by' means one lot of letters go next to another.
'rota' with letters rearranged gives 'aort'.
'aort'+'a'='AORTA'
(Other definitions for aorta that I've seen before include "Great artery in body" , "Trunk route" , "claret supplier" , "Bloody channel" , "Main artery of body" .)