Alpha-B crystallin in the normal human myocardium and cardiac conducting system

The alpha crystallins are major protein components of the ocular lens and show both structural and functional homology with the family of small heat shock proteins. alpha B crystallin is also present in various extra-lenticular tissues, with a high concentration in cardiac muscle. In this study, the myocardium and conducting system from 15 adult and 25 fetal and infant hearts were examined by immunohistochemistry using a previously characterized antiserum to alpha B crystallin. Contractile myocardium showed moderate staining, with particular localization to Z bands and intercalated discs. Fibres of the sino-atrial and atrio-ventricular nodes and His bundle showed less intense staining than contractile fibres, whereas fibres of the left and right bundle branches showed more intense staining. This distribution is similar to that previously demonstrated for the intermediate filament desmin. This observation, together with currently available evidence, suggests that cardiac alpha B crystallin may play a role in protecting the cytoskeleton during cell stress. For practical purposes, immunostaining with alpha B crystallin greatly facilitates the identification of cardiac conducting fibres.