Absence of utrophin in intercalated discs of human cardiac muscle

Utrophin is the autosomal homologue of dystrophin. In normal skeletal muscle it is localised only to neuromuscular and myotendinous junctions, nerves and vascular tissue. In Xp21 muscular dystrophies, utrophin is also detected on the sarcolemma of skeletal and cardiac muscle, while dystrophin is absent or reduced. In normal cardiac muscle, some reports have demonstrated utrophin at intercalated discs and T-tubules. We have re-examined the distribution of utrophin in normal human cardiac muscle using a panel of eight monoclonal antibodies against different epitopes in N- and C-terminal domains. In contrast to previous studies, utrophin was not detected at the intercalated 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 vascular system. In addition, our results show that the utrophin on cardiac blood vessels is full length, similar to that of skeletal muscle blood vessels.