TRP-Dependent Calcium Regulation in HCEC-12 Cells: Involvement of Ascorbic Acid and Cannabinoid Receptor Signaling
Louay Homsi1, Anisha Atul Bhamare1, Uwe Pleyer1,2
1Department of Ophthalmology, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, 13353 Berlin, Germany.
International Journal of Molecular Sciences
|May 13, 2026
Summary
L-ascorbic acid and cannabinoid agonists modulate calcium in human corneal endothelial cells. Their combined effect suggests TRP channels and CB1 receptors are key targets for corneal disorder treatments.
Area of Science:
- Cell Biology
- Ophthalmology
- Neuroscience
Background:
- Human corneal endothelium (HCE) is vital for corneal transparency.
- Altered intracellular calcium ([Ca2+]i) homeostasis is linked to HCE dysfunction.
- Transient receptor potential (TRP) channels and cannabinoid receptors (CB) regulate [Ca2+]i.
Purpose of the Study:
- To investigate the effects of L-ascorbic acid (Asc) and a CB agonist (WIN 55,212-2) on [Ca2+]i regulation in human corneal endothelial cells (HCECs).
- To explore the interaction between TRP channel activity and CB signaling in HCECs.
Main Methods:
- HCEC-12 cells were used as an HCE model.
- Intracellular calcium ([Ca2+]i) dynamics were measured using fura-2/AM fluorescence imaging.
- Membrane currents were analyzed via planar patch-clamp recordings.
Main Results:
- Asc (1 mM) increased [Ca2+]i, an effect partially blocked by TRPV1 and TRPV4 inhibitors.
- WIN (10 µM) induced [Ca2+]i transients, attenuated by CB1 inverse agonist AM251 and TRP channel blockers.
- Combined Asc and WIN treatments showed synergistic effects on [Ca2+]i elevation.
Conclusions:
- This study provides the first evidence of a functional interaction between TRP channels and CB signaling in HCECs.
- CB1 receptors appear to play a predominant role, as indicated by AM251's inhibitory effect.
- TRP channels and cannabinoid signaling represent potential therapeutic targets for corneal disorders.
Related Concept Videos
01:27Feedback Regulation of Calcium Concentration
Calcium is an essential signaling molecule required for various cellular functions. Calcium pumps and ion channels on cell and organellar membranes, such as those on the endoplasmic reticulum (ER), regulate calcium concentrations inside the cell. They remain closed, keeping the cytosolic calcium levels low at a resting state.
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
01:16Calmodulin-dependent Signaling
Calmodulin (CaM) is a calcium-binding protein in eukaryotes that controls various calcium-regulated cellular processes. It has four calcium-binding sites that bind calcium to form the calcium-calmodulin ( Ca2+-CaM) complex. GPCR stimulation increases the calcium levels in the cells that bind to CaM and induces a conformational change.
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
01:09GPCRs Regulate Adenylyl Cylase Activity
Some GPCRs transmit signals through adenylyl cyclase (AC), a transmembrane enzyme. AC helps synthesize second messenger cyclic adenosine monophosphate (cAMP). AC catalyzes cyclization reaction and converts ATP to cAMP by releasing a pyrophosphate. The pyrophosphate is further hydrolyzed to phosphate by the enzyme pyrophosphatase, which drives cAMP synthesis to completion. However, cAMP is rapidly degraded to 5′ AMP by the enzymes phosphodiesterase (PDE), preventing overstimulation of cells.
Two...
Two...
01:12GPCR Desensitization
G protein-coupled receptor (GPCR) signaling plays a crucial role in cell functioning. GPCR desensitization is an equally essential process. It allows cells to respond to changing environments and regain sensitivity to new stimuli while preventing unnecessary stimulation when no longer needed. Prolonged exposure to stimuli leads to GPCR desensitization. It involves blocking the receptors from binding and activating additional G proteins. This inhibits activation of downstream effectors, thereby...
01:15Receptor Downregulation in MVBs
Multivesicular bodies (MVBs) are mature endosomes that sort ubiquitinated proteins and then fuse with lysosomes to degrade the sorted proteins. Epidermal growth factor (EGF) and its receptor (EGFR) form a complex that can be internalized through endocytosis, sorted into an MVB, and later degraded.
The EGFR can initiate signaling pathways that lead to cell proliferation, migration, and differentiation. Overexpression of EGFR stimulates cells to proliferate. Excessive EGFR activation may...
The EGFR can initiate signaling pathways that lead to cell proliferation, migration, and differentiation. Overexpression of EGFR stimulates cells to proliferate. Excessive EGFR activation may...
01:30Ligand-Gated Ion Channel Receptor: Gating Mechanism
Ligand-gated ion channels are transmembrane proteins that play a vital role in intercellular communication and functions of the nervous system. They allow the influx of ions across the membrane once the neurotransmitter binds, allowing the subsequent transmission of electrical excitation across the neurons. Other ligand-gated ion channels, like the γ-aminobutyric acid (GABA) receptor, permit anions like chloride into the cells on the binding of the GABA molecule. Their entry into the cell...