Fig. 6. Functional expression of 3 and 8-G22R connexins in Xenopus oocytes. (A) Western blot analysis of Xenopus oocytes shows similar levels of 8-G22R and 3 proteins when expressed alone or co-injected. Equal amounts of oocyte membrane fractions were loaded into each lane, and the blots were probed with a polyclonal anti-8 connexin (left), or anti-3 connexin (right) antibody. Similar levels of 8-G22R and 3 protein synthesis were seen in individually and co-injected oocytes. Quantitation of band intensity by densitometry confirmed that levels of connexin expression were not statistically different (P>0.05). Densitometry values are the mean of three independent experiments. (B) 8-G22R connexin forms functional heteromeric channels with 3 connexin. Junctional conductance values were measured between oocyte pairs injected with wild-type 3, 8-G22R, co-injected 8-G22R and 3, or water. Oocyte pairs containing wild-type 3 alone (n=20), or co-injected 8-G22R and 3 (n=57) exhibited conductance values >100-fold higher than the pairs injected with water for the background value (n=40). However, conductance of co-injected 3 and 8-G22R was reduced 75% compared with 3 alone (P<0.05). Homotypic 8-G22R (n=55) cell pairs failed to produce levels of coupling that were significantly higher than background (P>0.05). Similarly, heterotypic 8-G22R/3 cell pairs, formed by pairing one oocyte expressing 3 with another injected with 8-G22R, were poorly coupled (n=16).