Loss of Cx43 augments ATP‐mediated calcium signals of osteoblast‐like cells

Abstract

Intercellular communication of osteoblast-like cells (OBL) is discussed to be a prerequisite for osseointegration of implants. This signaling involves changes of the intracellular calcium concentration ([Ca 2+ ] i ) which can be elicited by mechanical stimuli and are propagated from cell to cell. These [Ca 2+ ] i signals have originally been assumed to pass exclusively through gap junctions. However, substances such as purine nucleotides (ATP, UTP) are also released by osteoblasts upon mechanical stimulation and evoke [Ca 2+ ] i signals in neighboring cells after binding to purine receptors. In this investigation we studied the impact of the major gap junction protein connexin 43 (Cx43) on ATP-mediated calcium signaling of OBL in vitro. We compared OBL derived from calvaria of Cx43 deficient (Cx43-/-, Cx43+/-) and wild type animals (Cx43+/ +). While application of ATP to Cx43+/+ or Cx43+/-OBL evoked a single transient increase of [Ca 2+ ] i , the response of most Cx43-/-OBL was pronounced in that the initial [Ca 2+ ] i peak was larger and followed by 3-10 repetitive calcium waves. With respect to shape and number of peaks different types of responses co-existed in neighboring OBL, possibly pointing to differences in purinoceptor subtypes and/or filling states of intracellular calcium stores. Data show that ATP signaling of osteoblasts is changed in Cx43 deficient OBL, suggesting a compensatory role of purinoceptor mediated [Ca 2+ ] i signaling secondary to an impaired gap junction communication in Cx43-/-OBL.