A Novel Function of Thyrotropin as a Potentiator of Electrolyte Secretion from the Tracheal Gland

Abstract

Accumulating evidence suggests that thyrotropin (thyroid-stimulating hormone [TSH]) plays some roles in immunoregulation by an extrathyroidal action. Because airway submucosal glands are responsible for nonspecific and specific airway defense, we tested the effect of TSH on feline tracheal submucosal gland using a whole-cell patch-clamp technique, immunohistochemistry, and reverse transcription/polymerase chain reaction (RT-PCR). TSH potentiated neurotransmitter-induced ionic currents significantly in a dose-dependent manner. Acetylcholine (10(-)(8) M)- and norepinephrine (10(-)(7) M)-induced inward current (I(i)), which we previously showed to be a Cl(-) current, were increased to about 3-fold the pre-TSH control responses, respectively, by 2.0 ng/ml TSH; and to 6- and 23-fold the control values by 20.0 ng/ml TSH, respectively. TSH alone was without effect up to 20.0 ng/ml. Follicular stimulating hormone only slightly affected the I(i) (1. 5-fold the control). Analyses with immunohistochemistry and RT-PCR failed to identify TSH receptors on the glandular tissue. Maneuvers to raise the cellular adenosine 3',5'-cyclic monophosphate also failed to mimic the TSH-mediated potentiation. The TSH effect appeared to be mediated by a signaling pathway involving tyrosine kinase because its inhibitors (genistein and herbimycin A) abolished the augmentation completely, and interferon-gamma, a tyrosine kinase activator, imitated the TSH action on submucosal gland. Thus, TSH may be an important regulator of airway fluid secretion.

Flagellin/TLR5 signaling potentiates airway serous secretion from swine tracheal submucosal glands

“…]i. Moreover, we found that physiologically relevant, basic secretions from swine tracheal submucosal glands could be triggered by ϳ30 nM of ACh (16,17,31,38,39,44,45). The viability of all tested cells was confirmed by the occurrence of ionic responses after the subsequent addition of 30 nM of ACh.…”

“…The isolated glands were further dispersed enzymatically by incubating them with enzyme solution containing collagenase (200 U/ml) and DL-DTT (0.31 mg/ml) for 30 min at 37°C. After dispersion and a wash with centrifugation at 180 g, the cells were resuspended in a standard extracellular solution until use, as reported previously (16,17,31,38,39,44,45). In a series of experiments investigating the effect of blocking antibodies, anti-TLR 5 polyclonal antibody (10 g/ml) or nonspecific IgG (10 g/ml) was also preincubated with cells for 1 h at 37°C before use.…”

“…Membrane currents were monitored at two different holding potentials (Hps), i.e., 0 and Ϫ80 mV, which roughly corresponded to the Cl Ϫ and K ϩ equilibrium potential. The double current monitoring, i.e., alternate recording of the ionic currents corresponding to Hp of 0 and Ϫ80 mV, was accomplished by applying 200-ms voltage pulses of Ϫ80 mV at a frequency of 2 Hz to the pipette voltage of 0 mV (16,17,31,38,39,44,45 (16,17,31,38,39,44,45). The solutions included an extracellular (bath) solution of 120 mM NaCl, 4.7 mM KCl, 1.13 mM MgCl 2, 1.2 mM CaCl2, 10 mM glucose, and 10 mM HEPES and an intracellular (pipette) solution of 120 mM KCl, 1.13 mM MgCl 2, 0.5 mM EGTA, 1 mM Na2ATP, 10 mM glucose, and 10 mM HEPES.…”

“…The procedure to estimate the ionic responses was also applied in our previous reports (17,31,44,45). We first measured the area circumscribed with the current trace (I o or Ii) and baseline for 20 s (area under curve20) by using a digital planimeter (PLACOM, KP-92N; Koizumi, Tokyo, Japan).…”

“…Among these airway mucosal defense systems, airway serous secretion plays important roles in hydrating airway surfaces and flushing mucin glycoproteins out of the ducts, contributing to the maintenance of mucociliary transport (2,4,10,24,48). Human, feline, and swine tracheal gland acinar cells generate ionic currents in response to relatively low doses of cholinergic and ␣-adrenergic stimuli, and these currents are activated by the intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) raised by these neurotransmitters (16,31,38,44,45). The Ca 2ϩ -activated Cl Ϫ channel (CaCC) may play an important role in physiological basal secretions in the airways.…”