Fig. 6. (A) Occludin immunoblot of human Caco-2 cells, monkey BSC1 cells, canine MDCK cells, murine CMT64/61 cells and lung (mLung). In each case, a major band at 65-67 kDa is evident as well as other bands, as shown previously in occludin blots, including one at 62 and 58 kDa. The 58 kDa band (arrow) is where the TM4^- isoform would be expected to migrate. (B) Equally loaded lanes of confluent (Con) and subconfluent (Sub) Caco-2 cells with the major (65-67 kDa) and lowest migrating (58 kDa) bands indicated by arrows. Densitometric analysis reveals equivalent expression of the major band in confluent and subconfluent cells but significant upregulation of the 58 kDa band in subconfluent cells (^*P<0.001, n=12 replicates of each condition; experiment conducted three times).