Yonsei Med J.  2007 Aug;48(4):684-693. 10.3349/ymj.2007.48.4.684.

Heterogeneous Composition of Voltage-Dependent K+ Currents in Hepatic Stellate Cells

• Lee DH
• Kimm K
• Kim HL
• Han BG

• KMID: 2158176
• DOI: http://doi.org/10.3349/ymj.2007.48.4.684

Abstract

PURPOSE
Hepatic stellate cells (HSC) are a type of pericyte with varying characteristics according to their location. However, the electrophysiological properties of HSC are not completely understood. Therefore, this study investigated the difference in the voltage-dependent K(+) currents in HSC. MATERIALS AND METHODS: The voltage-dependent K(+) currents in rat HSC were evaluated using the whole cell configuration of the patch-clamp technique. RESULTS: Four different types of voltage-dependent K(+) currents in HSC were identified based on the outward and inward K(+) currents. Type D had the dominant delayed rectifier K(+) current, and type A had the dominant transient outward K(+) current. Type I had an inwardly rectifying K(+) current, whereas the non-type I did not. TEA (5mM) and 4-AP (2mM) suppressed the outward K(+) currents differentially in type D and A. Changing the holding potential from -80 to -40mV reduced the amplitude of the transient outward K(+) currents in type A. The inwardly rectifying K(+) currents either declined markedly or were sustained in type I during the hyperpolarizing step pulses from -120 to -150mV. CONCLUSION: There are four different configurations of voltage-dependent K(+) currents expressed in cultured HSC. These results are expected to provide information that will help determine the properties of the K(+) currents in HSC as well as the different type HSC populations.

Keyword

Hepatic stellate cells; voltage-dependent K(+) currents; different cell population

MeSH Terms

Animals
Cells, Cultured
Electric Conductivity/classification
Hepatocytes/*chemistry/classification
Ion Transport
Patch-Clamp Techniques
Potassium Channels, Voltage-Gated/*physiology
Rats

Figure

• 

  Fig. 1 Four types of voltage-dependent K+ currents in the cultured HSC. Voltage-dependent alterations in the cultured HSC membrane currents were measured under voltage-clamp conditions using the whole cell configuration of the patch-clamp technique. Representative traces of K+ currents in HSC cultured for 2 days were illustrated as type D (dominant delayed rectifier outward K+ current), type A (dominant transient outward K+ current), type ID (type D with inwardly rectifying K+ current), and type IA (type A with inwardly rectifying K+ current). K+ currents were elicited by the voltage ramps from -140 to 60mV in cells held at -80mV.

• 

  Fig. 2 Two types of voltage-dependent outward K+ currents. (A) Representative traces show type D and type A outward K+ currents in HSC cultured for 3 days. The currents were evoked by a series of depolarizing step pulses ranging from -80 to 70mV in 10mV increments for 200 ms, from a holding potential of -80mV. (B) Relationship between the command voltages and the outward K+ currents (n = 13 for type D, n = 7 for type A). The data are shown in mean ± SEM.

• 

  Fig. 3 Inhibitory effect of TEA on the voltage-dependent outward K+ currents. Representative traces of type D and A outward K+ currents were measured before and after the application of TEA (5mM) in HSC cultured for 2 days. The outward K+ currents were elicited by the step pulse to 20mV (Upper) and by the ramp pulse from -140 to 60 mV in cells held at -80mV (Lower).

• 

  Fig. 4 Inhibitory effect of 4-AP on the voltage-dependent outward K+ currents. Representative traces of type D and A outward K+ currents were measured before and after the application of 4-AP (2mM) in HSC cultured for 2 days. The outward K+ currents were elicited by the step pulse (Upper) and by the ramp pulse (Lower).

• 

  Fig. 5 Effect of holding potential on the voltage-dependent outward K+ currents. (A) Current responses in type D and A HSC cultured for 3 days were evoked by pulses from a different holding potential (Vh) of -80mV and -40mV with the voltage-clamp protocol shown in Fig. 2. (B) The peak amplitudes of the currents were plotted as a function of the voltages at different holding potentials (-80mV and -40mV).

• 

  Fig. 6 Inwardly rectifying K+ currents and time-dependent inactivation in cultured HSC. (A) Representative traces show inwardly rectifying K+ currents (type I) and inward K+ current which are not inwardly rectifying (non-type I) in HSC cultured for 5 days. The inward K+ currents were evoked by a series of voltage pulses ranging from -110 to -30mV with 10mV increments from a holding potential of -50mV. (B) Relationships between the command voltages and the inward K+ currents at the peak (n = 5). (C) At the test potentials ranging from -150 to -120mV, the inwardly rectifying K+ current showed significant time-dependent inactivation (decline type I) and sustained activation (sustaining type I) in HSC cultured for 5 days. (D) The peak and steady- state currents were plotted as a function of the voltages (n = 5). The data are shown in mean ± SEM.

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