Absence of utrophin in intercalated discs of human cardiac muscle

Utrophin is the autosomal homologue of dystrophin. In normal skeletal muscl e it is localised only to neuromuscular and myotendinous junctions, nerves and vascular tissue. In Xp21 muscular dystrophies, utrophin is also detecte d on the sarcolemma of skeletal and cardiac muscle, while dystrophin is abs ent or reduced. In normal cardiac muscle, some reports have demonstrated ut rophin at intercalated discs and T-tubules. We have re-examined the distrib ution of utrophin in normal human cardiac muscle using a panel of eight mon oclonal antibodies against different epitopes in N- and C-terminal domains. In contrast to previous studies, utrophin was not detected at the intercal ated discs or T-tubules, although labelling of blood vessels was strong. We conclude that the primary location of utrophin in normal heart is in the v ascular system. In addition, our results show that the utrophin on cardiac blood vessels is full length, similar to that of skeletal muscle blood vess els.