Tongju Li, Frank ter Veld, Hartwig R. Nürnberger, Frank Wehner Title Primary Human Hepatocytes Hypertonicity-activated Cation Channels in Primary Human Hepatocytes

Principles of Cell Volume Regulation H2OH2O Shrinkage hypertonic Swelling hypotonic RVD (regulatory volume decrease) K+K+ Cl - RVI (regulatory volume increase) Na +

Significance of Cell Volume Regulation  Homoiostasis: cope with the challenges of significant aniotonicity caused by high rates of substant transport or metabolism process.  Liver metabolism and gene expression: cell swelling favors the synthsis and/or inhibits the degradation of proteins, glycogen etc. Cell shrinkage induces opposite effect.  Apoptosis and proliferation  Epithelial transport : Na + coupled transport Na + -coupled transport across apical cell membrane of proximal renal tubules leads to accumulation of Na + and substrate [e.g., amino acids (AA)] and thus to cell swelling, which activates basolateral K + channels. From Lang F: Physiol Rev Jan;78(1):

Cell Volume Regulation and Proliferation A wide variety of mitogenic factors activate the Na + /H + exchanger and/or Na + -K + -2Cl - cotransport which are expected to increase cell volume. The proliferation of cells can be cut down by inhibition of these transporters. Osmotic alterations of cell volume indeed modify cell proliferation. Hypertonic shrinkage inhibits and slight osmotic cell swelling has been shown to accelerate cell proliferation. Proliferation Swelling

Cell volume Regulation and Apoptosis Apoptosis shrinkage RVI Cells displaying RVI are resistant against apoptosis. Cell swelling reduce apoptosis and cell shrinkage increase apoptosis. Apototic volume decrease (AVD) is an early prerequisite for apoptosis, and is mediated by activation of K + /Cl - channels: pharmacological block of these channels inhibits AVD as well as subsequent ultrastructural and biochemical events including cell death.

Cell volume regulation and apoptosis Speculative model outlining the possible participation of three highly interlinked events in apoptotic volume decrease. Double lines depict inhibitory events, and dotted lines depict undefined relationships. From Yu SP and Choi DW: PNAS 97 (2000) 9360–9362.

If......? Proliferation (Tumourgenesis) Apoptosis (Tumourdefense) RVD AVD swelling RVI If the RVI mechanisms (as well as swelling) in tumor cells can be selectively blocked......

Na + H + + K + + 2Cl - K + Cl - Na + K + Na + Rat Hepatocytes Mechanisms of RVI in Rat Hepatocytes Amiloride sensitive Gadolinium insensitive

HepG2 Cells Mechanisms of RVI in HepG2 Cells Non-selective cation channel Na + H + + K + + 2Cl - K + Cl - Na + K + Amiloride sensitive Gadolinium sensitive

Questions In the human tumour cell-line HepG2, a non- selective cation channel is expressed that is the main mechanism of RVI. Is the same channel expressed in (primary cultures of) non-tumorous human hepatocytes? Or is the channel the same but differentially regulated in these cells?

Primary Human Hepatocytes Preparation of Primary Human Hepatocytes Perfusion with collagenase cell suspension filtration

cell debris intact cells dead cells centrifugation cryo-preservation Primary Human Hepatocytes Preparation of Primary Human Hepatocytes Cell suspension 25% Percoll 50% Percoll Patch clamp

Patch clamp: Solutions and Protocol V I Cl - Na + Cl - K+K+ K+K+ bathpipetteE rev (mM) (mV) Na Cl K Vh (mV) Time (s)

Hypertonicity Increases Membrane Conductance Typical recording showing the reversal activation of whole-cell membrane current by hypertonicity

Changes of membrane conductance and reversal potentials Data are shown as mean±S.E., n =10. *: p<0.05, **:p<0.01 compared with iso Hypertonicity Activitates Channels hyper iso

Effect of Amiloride (10 -4 M) Typical recording showing the effect of 100 µM amiloride on hypertonicity-induced current

The Channels are Amiloride-sensitive hyper hyper + amiloride iso * * * * * Iso hyper hyper + amiloride Conductance (nS) * ** Reversal potentials (mV) ** Data are shown as mean±S.E, n=7. There are significant difference between iso and hyper or hyper+amiloride except for in the region of –10 mV ~ 0 mV.

The channels are Gadolinium-sensitive Hyper hyper + Gd 3+ iso * * * * * * Conductance (nS) * * Reversal potential (mV) ** iso hyper hyper+Gd 3+ Data are shown as mean±S.E, n=5. upper: * P<0.05 compared with iso or hyper + Gd 3+. Right: * P <0.05, ** P<0.01 compared with hyper.

Summary of pharmacology Pharmacology of hypertonicity-induced current. Each compound was used at 100 µM. #: P < 0.05; ###: P < compared with basal current (isotonicity); ***: P<0.001 compared with maximum hypertonic activation.

Permeability to NMDG + Typical recording showing changes in current and reversal potential in response to the Na + substitution by NMDG +

Summary of Ion-Selectivity Summary of ion-substitution experiments. Primary results showed the channel is unpermeable to Cl -. *: P < compared with Na +.

Rho A and Channel Activation C3 exoenzyme (which selecitvely inactivates Rho A) completely inhibites hypertonic curretn activation.

Summary 1.Hypertonicity increased membrane conductance of primary human hepatocytes through activation of cation channels. 2.The channel is non-selective to Na +, K +, Li +, and is also permeable to NMDG +, unpermeable to Cl -. 3.The cation channel is amiloride-sensitive; and is strongly blocked by gadolinium and flufenamate; 4.Rho A is part of the signalling machinery employed in channel activation.

Non-selective channels Gd 3+ Flu Amil P K + /P Na + P Li + /P Na + P NMDG + /P Na + Rat hepatocytes ?? Human hepatocytes HepG ? 0 Caco Hela