Regulation of ion channels in rat hepatocytes

 Patch-clamp studies have been performed to elucidate single ion channels in rat hepatocytes. In rat hepatocytes two types of ion channel have been identified: an inwardly rectifying K⁺ channel with a mean inward conductance of 55 ± 6.5 pS (n = 20) and a mean outward conductance of 25 ± 3.2 pS (n = 20) in the inside-out configuration with 145 mmol/l KCl on either side of the patch as well as an outwardly rectifying Cl^– channel with a mean outward conductance of 30 ± 4.5 pS (n = 8) and a mean inward conductance of 10 ± 2.3 pS (n = 6) in the inside-out configuration with symmetrical 145 mmol/l KCl. The open probability of these channels is virtually insensitive to Ca²⁺ activity on the intracellular side. Accordingly, the Ca²⁺ ionophore ionomycin had no effect on cell membrane potential. Dibutyryl-cAMP (db-cAMP) hyperpolarizes the cell membrane and increases the activity of the 55-pS inwardly rectifying K⁺ channel by reducing the duration of closure between bursts. Forskolin similarly hyperpolarizes the cell membrane. The inwardly rectifying K⁺ channel is inhibited by progesterone, while the outwardly rectifying Cl^– channel is insensitive to progesterone. Received: 21 May 1997 / Received after revision: 7 August 1997 / Accepted: 19 August 1997