Heteromeric Gap Junction Channels in Rat Hepatocytes in Which the Expression of Connexin26 is Induced

Abstract

More than one isotype of the gap junction channelforming protein subunit, known as connexin, are synthesized in most mammalian cells. Using a modified primary cell culture of rat hepatocytes, in which both connexin32 and connexin26 were expressed in a comparable degree, the molecular composition of connexin subtypes in a gap junction channel (i.e., homomeric or heteromeric) was studied. A fluorescent dye Lucifer Yellow-coupling among hepatocytes was blocked in the presence of 20 μM β-glycyrrhetinic acid, an antagonist for the gap junction channel. Similarly, either one of the antibodies raised against connexin32 or connexin26 completely inhibited dye-coupling activity among hepatocytes. In addition, we studied the dye-coupling properties at different extracellular pHs in two primary rat hepatocytes: one in which connexin26 was induced, and the other which expresses connexin32 as a major gap junction channel protein. The dye-coupling among the connexin26-induced hepatocytes was more sensitive to lowering pHs than among the normal hepatocytes, in which less than 5% of gap junction protein is connexin26. Taken together, data obtained in our study strongly suggest that the connexins (32 & 26) are assembled to form heteromeric, rather than homomeric, gap junction channels in the connexin26-induced rat hepatocytes.