Table 3.

Maturation of intercellular connections

Age range	Cardiomyocyte type	Key points	Citation
<0 years	Right and left ventricle	Intercalated discs begin to form in utero Immature intercalated discs are identifiable by 20 weeks of gestation; sparse gap junctions are identifiable between neighbouring cells by 32 weeks of gestation	Kim et al. (1992)
<1–15 years	Right ventricle	Intercalated discs develop with postnatal age Punctuated connexin pattern in neonatal heart tissue shifts progressively to transverse terminals of the cardiomyocyte with age. Gap junctions and adherens junctions show a mature pattern by ~6–7 years of age	Peters et al. (1994)
<0 years	Atria, ventricles and conduction tissue	Regional specificity of connexin proteins begins in utero Fetal connexin-40, -43 and -45 expression varies across tissues	Coppen et al. (2003)
<0–11 years	Left ventricle	Intercalated discs develop with postnatal age Increased adherens junctions, desmosomes, gap junctions and sodium channel localization to the intercalated discs during paediatric development	Vreeker et al. (2014)
<0–38 years	Atria, left and right ventricle	Gap junction proteins develop with age Connexin content and distribution vary between fetal, paediatric and adult tissue	Chen et al. ((1994)
<0–66 years	Right ventricle	Density and localization of gap junction proteins develop with age Connexin-43 protein expression decreases, whereas localization to intercalated discs increases	Salameh et al. (2014)