Diverse mediators modulate the chloride ion fluxes that drive lacrimal fluid production

Abstract

Purpose: To learn whether locally expressed and systemic mediators might modulate the cholinergically induced transepithelial Cl(-) fluxes that underlie lacrimal fluid production.

Methods: Reconstituted epithelial monolayers were exposed to a submaximal dose of the muscarinic agonist, carbachol (CCh), or to one of several paracrine mediators for 18 hours, then acutely stimulated with an optimal dose of CCh. Secretory Cl(-) fluxes were assessed as negative short-circuit currents (ISC).

Results: Exposure to IL-6 at concentrations of 1 and 10 ng/mL and IL-1β at 10 ng/mL significantly decreased CCh-induced Cl(-) secretion. Prolactin decreased CCh-induced Cl(-) secretion, but the extent of the decrease diminished as the prolactin concentration increased from 20 to 200 ng/mL. CCh, 10 μM, prevented CCh, 100 μM, from eliciting Cl(-) secretion. Exposure to histamine, 10 mM, prevented formation of confluent monolayers. Exposure to histamine, 1 mM, decreased CCh-induced Cl(-) secretion, whereas exposure to 5-HT, 1 mM, potentiated CCh-induced Cl(-) secretion.

Conclusions: Chronic exposure to inflammatory cytokines may significantly impair cholinergically induced lacrimal fluid production. Concentrations of prolactin within the high range of normal values also may impair fluid production, but this effect is reversed at levels associated with pregnancy. Autonomic neurotransmitters and paracrine mediators that signal through different G protein-coupled receptors appear to exert varying influences, which range from complete suppression to potentiation of cholinergically induced fluid production. Thus, some hormones and paracrine mediators may impair secretion in apparently homeostatic glands as well as diseased glands, whereas mediators produced by certain immune cell infiltrates may actually enhance fluid formation.

Figure 1

Influences of 18-hour exposure to IL-6 or IL-1β on I_SC induced by acute stimulation (arrows) with 100 μM CCh. The control monolayer was not exposed to added cytokines before measurement of I_SC. n = number of trials with replicate monolayers. All monolayers were from the same acinar cell preparation and were processed in parallel. P values refer to the significance of differences from the control determined by the Holm–Sidak method for pairwise multiple comparisons.

Figure 2

Influences of overnight exposure to prolactin on CCh-induced negative I_SC. The control monolayer was not exposed to added prolactin during the 18 hours before measurement of I_SC. n = number of replicate monolayers. All monolayers were from the same acinar cell preparation and were processed in parallel. P values refer to differences from control determined by the Holm–Sidak method for pairwise multiple comparisons. *I_SC after exposure to 200 ng/mL prolactin was significantly different from I_SC after exposure to 20 ng/mL prolactin and 100 ng/mL prolactin (P ≤ 0.008), but not different from control I_SC. Arrows indicate the time when the agonist was added.

Figure 3

Influence of 18-hour exposure to CCh, 10 μM, on I_SC induced by acute stimulation with the optimal CCh dose, 100 μM. Control monolayers were not exposed to CCh during the 18 hours before measurement of I_SC. n = number of replicate trials from the acinar cell preparation for which data are presented. Monolayers from each of seven separate acinar cell preparations studied were treated with 10 μM CCh, most in parallel with the other mediators. Similar results were observed in every preparation. Arrows indicate the time when the agonist was added.

Figure 4

(A) Influences of acute stimulation with histamine or 5-HT on basal- and CCh-induced I_SC. None of the monolayers was exposed to histamine, 5-HT, or CCh prior to measurement of I_SC. Neither histamine nor 5-HT acutely stimulated Cl secretion in the replicate trials indicated by the traces. (B) Influences of 18-hour exposure to histamine or 5-HT on I_SC induced by acute stimulation with CCh. Neither mediator altered Cl secretion at doses of 1 μM. At doses of 1 mM, histamine impaired CCh-induced Cl secretion, whereas 5-HT potentiated it. Results for each condition were pooled from monolayers from two separate acinar cell preparations. n = total number of replicate monolayers. P values in inset indicate significance of differences from control determined by the Holm–Sidak method for pairwise multiple comparisons. Arrows indicate the time when the agonist was added. Double arrows indicate that when there are two agonists, they are both added at the same time.