We isolated a mammalian gene whose expression transiently increased in response to intimal denudation of rabbit aorta. It was identical to a gene encoding a zinc transporter, ZNT5, reported very recently by others. Mice deficient for this gene showed poor growth and a decrease in bone density due to impairment of osteoblast maturation to osteocyte. More than 60% of male null mice died suddenly because of the bradyarrhythmias. Analysis of gene-expression profiles in murine hearts by means of an oligonucleotide microarray disclosed that a subset of genes encoding immediate-early response factors (IEGs) and heat shock proteins (HSPs) were down-regulated in Znt5-null mice. These results indicate that Znt5 protein plays an important role in maturation of osteoblasts and in maintenance of the cells involved in the cardiac conduction system, partly owing to dysregulated expression of IEGs and HSPs.