Electrophysiological properties of gap junction channels in hepatocytes isolated from connexin32-deficient and wild-type mice

Hepatocytes were isolated from wild-type and connexin32-deficient (Cx32-def icient) mice. Pairs of cells were chosen to study the electrical properties of gap junction channels using the dual voltage-clamp method. The total ga p junction currents revealed that Cx32-deficient hepatocytes express one ty pe of connexin (Cx26) and wild-type hepatocytes express two types of connex ins (Cx26 and Cx32). The unitary gap junction currents suggest that Cx32-de ficient cells have homotypic channels (Cx26-Cx26) while wild-type cells for m homotypic (Cx26-Cx26, Cx32-Cx32) and heterotypic channels (Cx26-Cx32), Ho motypic channels exhibited a main conductance and a residual conductance, b oth virtually insensitive to gap junction voltage (V-j) (Cx32-Cx32: gamma(j ,) (main)=31 PS, gamma(j, residual)=9 PS; Cx26-Cx26: gamma(j,) (main)=102 p S, gamma(j,) (residual) = 17 pS). Residual states were regularly seen in Cx 32-Cx32 channels, but rarely in Cx26-Cx26 channels. Heterotypic channels sh owed a main conductance and a residual conductance. The former was sensitiv e to V-j (average y(j, main) = 52 pS). The electrophysiological data sugges t that Cx32 hemichannels are more abundant than Cx26 hemichannels in prenat al (ratio 4:1) and adult wild-type hepatocytes (ratio 23:1) and that the to tal number of gap junction channels is larger in prenatal cells than in adu lt cells. The diversity of the relationship g(j, ss)/g(j, inst) = f(V-j) (g (j,) (ss):gap junction conductance at steady state: g(j, inst): Instantaneo us gap junction conductance; V-j: transjunctional voltage) seen in wild-typ e cells suggests that the ratio Cx26/Cx32 hemichannels is variable among he patocytes. A comparison of total and unitary conductances implies that Cx26 hemichannels are downregulated in Cx32-deficient cells and that docking be tween Cx26 and Cx32 hemichannels occurs randomly. While the gap junction cu rrents are compatible with homotypic and heterotypic channels, the presence of heteromeric channels cannot be excluded.