Properties of connexin40 gap junction channels endogenously expressed and 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 connexin40 (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 amounts 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 compare properties of endogenously and exogenously expressed Cx40 channels we have transfected Jeg-3 cells with rat Cx40. Recordings with dual whole-cell methods were used to determine the junctional conductance (gj) in the various cell lines and transfectants. Cx40 channels exogenously expressed in Jeg-3 cells demonstrated steep voltage sensitivity in the transjunctional voltage range of +/-30 to +/-40 mV and a unitary 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 conductance of about 30 pS, exclusively in BeWo cells. Between JAr cell pairs we determined a gj of 10 nS and unitary conductances were predominantly 100 and 152 pS. Voltage dependence was less sensitive in JAr cells compared to Cx40 transfectants and BeWo cells. Thus, coexpression of Cx43 and Cx40 leads to a macroscopic conductance with a mixture of properties expected for each connexin, whereas single-channel properties of each connexin type are maintained.