Calcium waves between astrocytes from Cx43 knockout mice

Gap junctions are regarded as the primary pathway underlying propagation of Ca²⁺ waves between astrocytes, although signaling through extracellular space may also contribute. Results obtained from astrocytes cultured from sibling Cx43 knockout (KO) and wild-type (WT) mice in six litters showed that Ca²⁺ waves propagated more slowly in Cx43 KO than in WT astrocytes; however, because this difference in velocity was only seen in conditions where cell confluence was higher in WT than KO astrocytes, it is attributable to differences in plating density. By contrast, density-independent differences were observed in the amplitudes of the Ca²⁺ responses (15% smaller in KO astrocytes) and efficacy of spread (to 14% fewer cells in KO astrocytes). Blockade of purinergic receptors with suramin reduced the velocities of the waves by 40% in WT and KO astrocytes and reduced the amplitudes by 20% and 6%, respectively. In the presence of heptanol, Ca²⁺ waves spread to only 30% of the cells, with a 70% reduced velocity and 30% reduced amplitude. It is concluded that the propagation of Ca²⁺ waves between astrocytes from Cx43 KO mice is not so greatly affected as expected by deletion of the major gap junction protein between these cells. The residual 5% coupling contributed by the additional connexins (Cx40, Cx45, and Cx46) expressed in KO astrocytes still suffices to provide a more substantial portion of Ca²⁺ wave propagation than does signaling through extracellular purinergic pathways. These studies demonstrate that, even with severely reduced junctional conductance, Cx43 KO astrocytes are capable of performing long-range Ca²⁺ wave signaling, perhaps preserving one mechanism critical to neural function.