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Journal of Histochemistry and Cytochemistry, Vol. 47, 383-392, March 1999, Copyright © 1999, The Histochemical Society, Inc.

ARTICLE

Myotonic Dystrophy Protein Kinase Expressed in Rat Cardiac Muscle Is Associated with Sarcoplasmic Reticulum and Gap Junctions

Isabella Mussinia, Donatella Birala, Oriano Marinb, Sandra Furlana, and Sergio Salvatoria
a Department of Biomedical Sciences and CNR Unit for Muscle Biology and Physiopathology, School of Medicine, University of Padova, Padova, Italy
b CRIBI Biotechnology Center, University of Padova, Padova, Italy

Correspondence to: Sergio Salvatori, Dept. of Biomedical Sciences, University of Padova, Viale Giuseppe Colombo 3 (ex Via Trieste 75), 35121 Padova, Italy.

Myotonic dystrophy (DM) is one of the most prevalent muscular diseases in adults. The molecular basis of this autosomal disorder has been identified as the expansion of a CTG repeat in the 3' untranslated region of a gene encoding a protein kinase (DMPK). The pathophysiology of the disease and the role of DMPK are still obscure. It has been previously demonstrated that DMPK is localized at neuromuscular junctions, myotendinous junctions, and terminal cisternae of the sarcoplasmic reticulum (SR), in the skeletal muscle, and at intercalated discs in the cardiac muscle. We report here new findings about specific localization of DMPK in the heart. Polyclonal antibodies raised against a peptide sequence of the human DMPK were used to analyze the subcellular distribution of the protein in rat papillary muscles. Confocal laser microscopy revealed a strong although discontinuous reactivity at intercalated discs, together with transverse banding on the sarcoplasm. At higher resolution with immunogold electron microscopy, we observed that DMPK is localized at the cytoplasmic surface of junctional and extended junctional sarcoplasmic reticulum, suggesting that DMPK is involved in the regulation of excitation–contraction coupling. Along the intercalated disc, DMPK was found associated with gap junctions, whereas it was absent in the two other kinds of junctional complexes (fasciae adherentes and desmosomes). Immunogold labeling of gap junction purified fractions showed that DMPK co-localized with connexin 43, the major component of this type of intercellular junctions, suggesting that DMPK plays a regulatory role in the transmission of signals between myocytes. (J Histochem Cytochem 47:383–392, 1999)

Key Words: myotonic dystrophy protein kinase, DMPK, immunoelectron localization, cardiac muscle, gap junctions, connexin 43, terminal cisternae, sarcoplasmic reticulum, excitation–contraction coupling


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