Permeance of Novikoff Hepatoma Gap Junctions: Quantitative Video Analysis of Dye Transfer

Fluorescent dyes are commonly used to study permeable (gap) junctions, but only rarely have quantitative values for junctional dye permeability been determined. In the present study, junctional permeance (PA, i.e., the product of the junctional permeability coefficient,P, times the junctional area,A) to Lucifer Yellow CH (LY) has been obtained for pairs of Novikoff hepatoma cells. Dye was microinjected into one cell and the subsequent transfer monitored by a SIT camera and recorded on video tape. The intensities of fluorescence in the injected and “recipient” cell were measured using a Digisector (Microworks) digitizing board and an Apple II Plus computer to analyze the video records. These changes in intensity, along with an estimate of volume of the spherical cells, were used to calculate the junctional permeance (PA) of cell pairs according to Fick's diffusion equation. Junctional permeances show considerable variation ranging from 0.08×10−11 to 27.0×10−11 cm3/sec. Using the meanPA and a previous estimate of the mean number of junctional channels per interface in the Novikoff cultures, a value for diffusion coefficient of LY through gap junctions is calculated to be about 1.4×10−6 cm2/sec. There is a general proportionality between meanPA and cell volume for hepatoma cell pairs of a certain size range. Such a relationship between cell volume and junctional capacity suggests one source of variation ofPA. Other possible sources, e.g., related to position in the cell cycle, are discussed.