Electrophysiological Properties of Gap Junctions between Dissociated Pairs of Rat Hepatocytes

Physiological properties of isolated pairs of rat hepatocytes were examined within 5 h after dissociation. These cells become round when separated, but cell pairs still display membrane specializations. Most notably, canaliculi are often present at appositional membranes which are flanked by abundant gap and tight junctions. These cell pairs are strongly dye-coupled; Lucifer Yellow CH injected into one cell rapidly diffuses to the other. Pairs of hepatocytes are closely coupled electrically. Conductance of the junctional membrane is not voltage sensitive: voltage clamp studies demonstrate that g j is constant in response to long (5 s) transjunctional voltage steps of either polarity (to > ±40 mV from rest). Junctional conductance ( g j) between hepatocyte pairs is reduced by exposure to octanol (0.1 mM) and by intracellular acidification. Normal intracellular pH ( pH i), measured with a liquid ion exchange microelectrode, was generally 7.1-7.4, and superfusion with saline equilibrated with 100% CO2 reduced pH i to 6.0-6.5. In the pH i range 7.5-6.6, g j was constant. Below pH 6.6, g j steeply decreased and at 6.1 coupling was undetectable. pH i recovered when cells were rinsed with normal saline; in most cases g j recovered in parallel so that g j values were similar for pHs obtained during acidification or recovery. The low apparent pK and very steep pH i- g j relation of the liver gap junction contrast with higher pKs and more gradually rising curves in other tissues. If H+ ions act directly on the junctional molecules, the channels that are presumably homologous in different tissues must differ with respect to reactive sites or their environment.