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

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 ([Ca2+]i ) which can be elicited by mechanical stimuli and are propagated from cell to cell. These [Ca2+]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 [Ca2+]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 [Ca2+]i, the response of most Cx43‐/‐ OBL was pronounced in that the initial [Ca2+]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 [Ca2+]i signaling secondary to an impaired gap junction communication in Cx43‐/‐ OBL. Der Verlust von Connexin43 verstärkt ATP‐vermittelte Kalziumsignale osteoblastenartiger Zellen Die interzelluläre Kommunikation zwischen Osteoblasten‐ähnlichen Zellen (OBL) wird als wichtige Voraussetzung für die Osseointegration von Knochenimplantaten angesehen. Diese Kommunikation beruht zum Teil auf Änderungen der intrazellulären Kalzium Konzentration ([Ca2+]i ), die durch mechanische Reize ausgelöst werden können und sich von Zelle zu Zelle ausbreiten. Früher nahm man an, dass sich Kalzium‐Signale ausschließlich über gap junctions ausbreiten. Durch mechanische Stimulation werden jedoch auch Purin‐Nukleotide (ATP,UTP) von OBL freigesetzt, die an Rezeptoren der Nachbarzellen binden und dort ebenfalls Kalziumtransienten auslösen. In dieser Untersuchung wollten wir den Einfluss von Cx43, dem wichtigsten gap junction Protein der OBL, auf ATP‐vermittelte Kalzium‐Signale testen. Dazu verglichen wir OBL‐Zellen aus Kalvarien‐Kulturen Cx43‐defizienter Mäuse (Cx43‐/‐, Cx43+/