Mechanosensitive Cl⁻ secretion in biliary epithelium mediated through TMEM16A

Abstract

Bile formation by the liver is initiated by canalicular transport at the hepatocyte membrane, leading to an increase in ductular bile flow. Thus, bile duct epithelial cells (cholangiocytes), which contribute to the volume and dilution of bile through regulated Cl(-) transport, are exposed to changes in flow and shear force at the apical membrane. The aim of the present study was to determine if fluid flow, or shear stress, is a signal regulating cholangiocyte transport. The results demonstrate that, in human and mouse biliary cells, fluid flow, or shear, increases Cl(-) currents and identify TMEM16A, a Ca(2+)-activated Cl(-) channel, as the operative channel. Furthermore, activation of TMEM16A by flow is dependent on PKCα through a process involving extracellular ATP, binding purinergic P2 receptors, and increases in intracellular Ca(2+) concentration. These studies represent the initial characterization of mechanosensitive Cl(-) currents mediated by TMEM16A. Identification of this novel mechanosensitive secretory pathway provides new insight into bile formation and suggests new therapeutic targets to enhance bile formation in the treatment of cholestatic liver disorders.

Regulators of Cholangiocyte Proliferation

“…Cholangiocytes possess cilia on their apical surface that act as mechanoreceptors, chemosensors, and osmosensors 38 . Shear stress along the apical membrane of cholangiocytes is detected by cilia, resulting in upregulation of Cl − currents via TMEM16A (aka anoctamin), a Ca 2+ -activated Cl − channel 39 . This process is dependent on PKC-α, extracellular ATP, purinergic P2 receptors, and increases in intracellular Ca 2+ concentration 39 .…”

“…Shear stress along the apical membrane of cholangiocytes is detected by cilia, resulting in upregulation of Cl − currents via TMEM16A (aka anoctamin), a Ca 2+ -activated Cl − channel 39 . This process is dependent on PKC-α, extracellular ATP, purinergic P2 receptors, and increases in intracellular Ca 2+ concentration 39 . Inhibition of CFTR did not change flow-stimulated currents in their studies, suggesting a different mechanism of Cl − transport when cholangiocytes are exposed to shear forces 39 .…”

“…This process is dependent on PKC-α, extracellular ATP, purinergic P2 receptors, and increases in intracellular Ca 2+ concentration 39 . Inhibition of CFTR did not change flow-stimulated currents in their studies, suggesting a different mechanism of Cl − transport when cholangiocytes are exposed to shear forces 39 . The key proteins involved in mechanosensation are polycystin-1 and polycystin-2.…”

Functional crosstalk between the adenosine transporter CNT3 and purinergic receptors in the biliary epithelia

“…Although less well known, the occurrence of P2-type receptors at the basolateral domain of cholangiocytes has also been reported [14,15]. By acting on these P2 receptors ATP triggers an increase in intracellular Ca 2+ , which results in the activation of K + and Cl À channels [16].…”

Fluid shear stress enhances the cell volume decrease of osteoblast cells by increasing the expression of the ClC-3 chloride channel

“…Various in vitro loading techniques, such as cell swelling, substrate stretch loading and fluid shear stress (FSS), are used in the study of osteocyte response to mechanical stimulation. However, the majority of studies do not recapitulate osteoblast anabolism under mechanical stimulation, including the activation of intracellular chloride ions, chloride channel genes and channel proteins (3)(4)(5)(6)(7). In fact, studies have shown that numerous ion channels [such as Ca 2+ channels (8) and K + channels (9)] have a role in osteogenic differentiation.…”