Thermosensitive transient receptor potential channels (thermo-TRPs) in human corneal epithelial cells

摘要

Thermosensitive transient receptor potential proteins (TRPs) such as TRPV1-TRPV4 are all heat-activated non-selective cation channels that are modestly permeable to Ca²⁺. TRPV1, TRPV3 and TRPV4 functional expression were previously identified in human corneal epithelial cells (HCEC). However, the membrane currents were not described underlying their activation by either selective agonists or thermal variation. This study characterized the membrane currents and [Ca ²⁺]i transients induced by thermal and agonist TRPV1 and 4 stimulation. TRPV1 and 4 expressions were confirmed by RT-PCR and TRPV2 transcripts were also detected. In fura2-loaded HCEC, a TRPV1-3 selective agonist, 100 µM 2-aminoethoxydiphenyl borate (2-APB), induced intracellular Ca²⁺ transients and an increase in non-selective cation outward currents that were suppressed by ruthenium-red (RuR) (10–20 µM), a nonselective TRPV channel blocker. These changes were also elicited by rises in ambient temperature from 25 °C to over 40 °C. RuR (5 µM) and a selective TRPV1 channel blocker capsazepine (CPZ) (10 µM) or another related blocker, lanthanum chloride (La³⁺) (100 µM) suppressed these temperature-induced Ca²⁺ increases. Planar patch-clamp technique was used to characterize the currents underlying Ca²⁺ transients. Increasing the temperature to over 40 °C induced reversible rises in non-selective cation currents. Moreover, a hypotonic challenge (25 %) increased non-selective cation currents confirming TRPV4 activity. We conclude that HCEC possess in addition to thermo-sensitive TRPV3 activity TRPV1, TRPV2 and TRPV4 activity. Their activation confers temperature sensitivity at the ocular surface, which may protect the cornea against such stress.