Nerve Growth Factor Modulates Regulatory Cell Volume Behavior via Stimulating TRPV1, TRPM8 Channels and Inducing Ca2+ Signaling in Human Conjunctival Epithelial Cells

NGF plays important roles in ocular surface homeostasis and different pathological conditions. One effect includes promoting conjunctival epithelial cell differentiation and mucin secretion. This study characterizes the individual roles of TRPV1 and TRPM8 channel activity in mediating the effects of NGF on intracellular Ca²⁺ regulation and its alteration of regulatory cell volume responses to anisosmotic challenges in human conjunctival epithelial cells (IOBA-NHC). With fura-2/AM-loaded cells, the effects of 40 µM capsaicin and 20 µM AMG 9810 on Ca²⁺ regulation confirm functional TRPV1 expression. TRPM8 expression is evident since 500 µM menthol and 20 µM AMTB have opposing effects on [Ca²⁺]_i. AMG 9810 and AMTB (both 20 µM) suppress the responses to NGF (100 ng/mL). With calcein/AM-loaded cells, the effects of these mediators are evaluated on apparent cell volume responses induced by an anisosmotic challenge. NGF decreases the apparent cell volume that AMG 9810 suppresses, whereas AMTB (both 20 µM) augments this response. Therefore, NGF interacts with TRPV1 and TRPM8 to induce opposing effects on cell volume regulatory behavior. These opposing effects suggest that the signaling pathways and effectors that mediate responses to TRPV1 and TRPM8 activation are not the same.