Abstract
Costameres, vinculin‐containing structures found in skeletal and cardiac muscle, are thought to anchor the Z‐discs of the peripheral myofibrils to the sarcolemma. Several lines of evidence indicate that two different sets of costameres, integrin‐ and N‐cadherin‐based, are present in cardiac muscles. In this study, immunoblot analysis was used to study the expression of N‐cadherin, α‐catenin, β‐catenin, vinculin, talin, and laminin in rat cardiac muscles at embryonic days 15 and 19, the day of birth (postnatal day 0), postnatal weeks 1, 2, 3, and 4, and in the adult. Double immunofluorescence microscopy was performed to study the spatial and temporal distribution of these two sets of costameres in rat cardiomyocytes. Costameric staining for N‐cadherin, codistributed with β‐catenin, was strong from embryonic day 15 up to postnatal week 2, gradually decreased after postnatal week 3, and was undetectable at postnatal week 4 and in the adult. Confocal microscopy showed that N‐cadherin colocalized with α‐actinin at cortical myofibrils. Double‐labeling of β‐catenin and talin indicated the coexistence of N‐cadherin/catenin‐ and integrin/talin‐based costameres in rat cardiac muscle. Although β‐catenin and vinculin were co‐localized at the costamere of cardiomyocytes from embryonic day 15 to postnatal week 3, staining for β‐catenin or talin was mutually exclusive at all stages examined. These results demonstrate the simultaneous, but mutually exclusive, existence of N‐cadherin/catenin‐ and integrin/talin‐based costameres in rat cardiomyocytes between late embryonic stages and postnatal week 3, while only integrin/talin‐based costameres were found in adult rats. The N‐cadherin/catenin‐based costameres in rat cardiac muscles may play a role in myofibrillogenesis similar to that of their counterparts in cultured cardiomyocytes. J. Cell. Biochem. 84: 717–724, 2002. © 2002 Wiley‐Liss, Inc.