Transmembrane potentials in guinea‐pig hepatocytes

1. In pieces of guinea‐pig liver with an intact capsule, the mean resting potential ( E ) is −49·8 mV, close to the value for in vivo hepatocytes and significantly higher than a similar preparation of rat liver. E is considerably less than the calculated K equilibrium potential of about −90 mV. 2. Changes in [K + ] o in the range of 0–10 m M produce almost no change in E . At [K + ] o above 20 m M , a tenfold increase produces only a 33 mV depolarization. The results with changing [K + ] o are the same in Cl − free solutions (isethionate substitution) or when the [K + ] o [Cl − ] o product is kept constant. E rapidly returned to normal in liver pieces returned to Ringer after prolonged soaking in high K + solution. 3. Changes in [Na + ] o , [Cl − ] o , [H + ] o , [Ca 2+ ] o or [Mg 2+ ] o have little effect on E . Simultaneous variation of [Na + ] o and [Cl − ] o in opposite directions to maximize predicted changes in E also has only a minimal effect on E . 4. Cyanide (5 m M ) or ouabain (10 −4 M ) cause depolarization, so there is no reason to believe that pumps sensitive to these poisons are normally lowering resting potential. Part of the normal E may be produced by an electrogenic ouabain‐sensitive ion pump. 5. The data is interpreted by using a form of the constant field equation developed by Brading & Caldwell (1971). Application of this method yields P Na / P K less than 0·04, P Cl / P K approximately 0·3. Additional terms, x and y , are required to account for the behaviour of E . Their physical basis remains undetermined. 6. Suggestions are presented for further study and for the application of the method of Brading & Caldwell to other non‐excitable cells and to excitable cells in low [K + ] o , in which E is poorly understood.