Actions of spermicidal and virucidal agents on electrogenic ion transfer across human vaginal epithelium in vitro.

Human ectocervical tissue was removed at operation over the menstrual cycle mounted as a sheet in vitro in an Ussing-style chamber and incubated in bicarbonate saline. The net electrogenic ion transport was measured as the short-circuit current (Isc in muamps/cm2) and was characterised as mainly (60-86%) an amiloride-sensitive electrogenic Na+ transport (lumen to serosa). Serosal application of amiloride had no effect. Serosal application of ouabain, a selective Na(+)-pump inhibitor, reduced the Isc to near zero but neither theophylline (10 mM) nor furosemide (1 mM) had any action. The data are compatible with a model ectocervical vaginal cell having an amiloride-sensitive Na+ entry mechanism at the lumenal membrane and a Na(+)-pump at the basolateral membrane removing the ion from the cell. The effects of the putative virucides, chlorhexidine and benzalkonium chloride, were tested on the preparation. Mucosally added chlorhexidine (2 mg/ml) had no effect on the Isc or tissue resistance but benzalkonium chloride, at concentrations between 0.06-1.2%, caused a rapid fall in the Isc. At the highest concentration this was only partly reversible even after two washes with fresh buffer. At the lowest concentration (0.03%) benzalkonium chloride sometimes caused an initial increase in the Isc which then fell to zero. In all the tissues even after the Isc was reduced to near zero, nigrosin left in contact with the tissue for 5 min. did not enter and stain the cells, indicating the detergent had a selective membrane action rather than causing a non-specific increase in permeability. The preparation allows objective measurements to be made of the initial acute membrane actions of putative spermicides and virucides on human vaginal ectocervical epithelial cells and offers a new approach of assessing their pharmacological/toxicological actions.