Permeability of a cell junction during intracellular injection of divalent cations

Divalent cations are microinjected into Chironomus salivary gland cells while the cell-to-cell passage of fluorescein (330 dalton) and electrical coupling are monitored. Injections of Ca and Mg that substantially depolarize the cells produce block or marked slowing fluorescein passage, accompanied by electrical uncoupling. Injections of Ca, Mg or Sr that cause little depolarization, and presumably smaller elevation of divalent cation concentration in the cytoplasm, produce block or marked slowing of fluorescein passage with little or no detectable electrical uncoupling. This partial uncoupling may reflect total closure of a fraction of the channels in junctional membrane or partial closure of all channels.