The Dry Eye Zone

Rebecca's Blog

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Bioelectric analysis of what dry eye does to goblet cells & mucin

This will mostly only be of interest to hardcore dry eye nerds.

But I thought it was fascinating. (Whoops, did I just define myself as a nerd?)

Am J Physiol Cell Physiol. 2018 Apr 18. doi: 10.1152/ajpcell.00077.2018. [Epub ahead of print]
Role of ion channels in the functional response of conjunctival goblet cells to dry eye.
Puro DG1.

Abstract
Optimal vision requires an ocular surface with a stable tear film whose many critical tasks include providing >70% of the eye's refractive power. However for millions, tear film instability produces uncomfortable sight-impairing dry eye. Despite the multitude of etiologies for dry eye, a universal hallmark is hyperosmolarity of the tear film. Presently, knowledge of how the ocular surface responds to hyperosmolarity remains incomplete with little understood about the role of ion channels. This bioelectric analysis focused on conjunctival goblet cells whose release of tear-stabilizing mucin is a key adaptive response to dry eye. In freshly excised rat conjunctiva, perforated-patch recordings demonstrated that a {greater than or equal to}10% rise in osmolarity triggers goblet cells to rapidly generate a ~15-mV hyperpolarization due to the oxidant-dependent activation of KATP channels. High-resolution membrane capacitance measurements used to monitor exocytosis revealed that this hyperpolarization results in a >4-fold boost in exocytotic activity evoked by cholinergic input, which in vivo occurs via a neural reflex and depends chiefly on calcium influxing down its electro-gradient. We discovered that this adaptive response is transient. During 30-80 min of hyperosmolarity, development of a depolarizing nonspecific cation conductance fully counterbalances the KATP-driven hyperpolarization and thereby, eliminates the exocytotic boost. We conclude that hyperosmotic-induced hyperpolarization is a previously unappreciated mechanism by which goblet cells respond to transient ocular dryness. Loss of this voltage increase during long-term dryness/hyperosmolarity may account for the clinical conundrum that goblet cells in chronically dry eyes can remain filled with mucin even though the tear film is hyperosmotic and mucin-deficient.