PROPERTIES OF CONNEXIN40 GAP JUNCTION CHANNELS ENDOGENOUSLY EXPRESSEDAND EXOGENOUSLY OVEREXPRESSED IN HUMAN CHORIOCARCINOMA CELL-LINES

We have investigated the properties of gap junction channels of three human malignant trophoblast (choriocarcinoma) cell lines: BeWo, Jeg-3 and JAr, as well as in Jeg-3 cells stably transfected with rat connex- in40 (Cx40). Reverse-transcriptase polymerase chain reaction (RT-PCR), Northern blot analysis and immunostaining demonstrated expression of Cx40 in BeWo and JAr cell lines. JAr cells also expressed minor amount s of Cx43. Very low levels of Cx40 transcripts were revealed by RT-PCR in parental Jeg-3 cells, but Cx40 protein was not detected. To compar e properties of endogenously and exogenously expressed Cx40 channels w e have transfected Jeg-3 cells with rat Cx40. Recordings with dual who le-cell methods were used to determine the junctional conductance (g(j )) in the various cell lines and transfectants ants. Cx40 channels exo genously expressed in Jeg-3 cells demonstrated steep voltage sensitivi ty in the transjunctional voltage range of +/-30 to +/-40 mV and a uni tary mainstate conductance of 175 pS, values which are similar to the data obtained from endogenously expressed Cx40 in BeWo cell pairs. In addition greater driving forces resulted in a lower unitary conductanc e of about 30 pS, exclusively in BeWo cells. Between JAr cell pairs we determined a g(j) of 10 nS and unitary conductances were predominantl y 100 and 152 pS. Voltage dependence was less sensitive in JAr cells c ompared to Cx40 transfectants and BeWo cells. Thus, coexpression of Cx 43 and Cx40 leads to a macroscopic conductance with a mixture of prope rties expected for each connexin, whereas single-channel properties of each connexin type are maintained.