The gap junction protein connexin43 (Cx43) plays an important role in bone development and its homeostasis. Therefore, it is important that the Cx43 expression is kept at a high-level in bone tissues under normal conditions. To investigate the mechanism to keep Cx43 expression level, the effects of protein kinase inhibitors on the basal expression of Cx43 were examined. It was found that the specific P13K inhibitor LY294002 significantly decreased the steady-state expression levels of Cx43 mRNA and protein in osteoblastic cell line, MC3T3-E1 cells. Furthermore, dominant-negative Akt expression reduced both Cx43 expression and gap junction activity. These results suggest an important role of P13k/Akt in the regulation of basal Cx43 expression. A promoter assay for Cx43 and an actinomycin D chase experiment revealed that P13K/Akt modulated Cx43 expression post-transcriptionally via mRNA stability. The present findings could provide new insights into the molecular understanding of Cx43 expression. (C) 2009 Elsevier Inc. All rights reserved.