Douglas L. Bovell

Latherin: a surfactant protein of horse sweat and saliva.

Horses are unusual in producing protein-rich sweat for thermoregulation, a major component of which is latherin, a highly surface-active, non-glycosylated protein. The amino acid sequence of latherin, determined from cDNA analysis, is highly conserved across four geographically dispersed equid species (horse, zebra, onager, ass), and is similar to a family of proteins only found previously in the oral cavity and associated tissues of mammals. Latherin produces a significant reduction in water surface tension at low concentrations (≤1 mg ml−1), and therefore probably acts as a wetting agent to facilitate evaporative cooling through a waterproofed pelt. Neutron reflection experiments indicate that this detergent-like activity is associated with the formation of a dense protein layer, about 10 Å thick, at the air-water interface. However, biophysical characterization (circular dichroism, differential scanning calorimetry) in solution shows that latherin behaves like a typical globular protein, although with unusual intrinsic fluorescence characteristics, suggesting that significant conformational change or unfolding of the protein is required for assembly of the air-water interfacial layer. RT-PCR screening revealed latherin transcripts in horse skin and salivary gland but in no other tissues. Recombinant latherin produced in bacteria was also found to be the target of IgE antibody from horse-allergic subjects. Equids therefore may have adapted an oral/salivary mucosal protein for two purposes peculiar to their lifestyle, namely their need for rapid and efficient heat dissipation and their specialisation for masticating and processing large quantities of dry food material.

Ultrastructure of the hyperhidrotic eccrine sweat gland

Background Hyperhidrosis is the secretion of inappropriately large amounts of sweat by eccrine glands; it can be very debilitating. Little is known of the causes of primary hyperhidrosis.

The absence of apoeccrine glands in the human axilla has disease pathogenetic implications, including axillary hyperhidrosis

Background  The existence of a third type of sweat gland in human axillary skin, the apoeccrine gland, with a capacity to produce much higher sweat output than the eccrine gland, was proposed from examination of microdissected glands. However, previous studies of axillary skin glands did not examine the entire individual glandular structure via serial sections and the markers used to identify the different glands gave conflicting results and, hence, the existence of the apoeccrine gland remains controversial.

The secretory clear cell of the eccrine sweat gland as the probable source of excess sweat production in hyperhidrosis

Abstract:  Primary hyperhidrosis is characterized by excessive sweating in palmar, plantar and axillary body regions. Gland hypertrophy and the existence of a third type of sweat gland, the apoeccrine gland, with high fluid transporting capabilities have been suggested as possible causes. This study investigated whether sweat glands were hypertrophied in axillary hyperhidrotic patients and if mechanisms associated with fluid transport were found in all types of axillary sweat glands. The occurrence of apoeccrine sweat glands was also investigated. Axillary skin biopsies from control and hyperhidrosis patients were examined using immunohistochemistry, image analysis and immunofluorescence microscopy. Results showed that glands were not hypertrophied and that only the clear cells in the eccrine glands expressed proteins associated with fluid transport. There was no evidence of the presence of apoeccrine glands in the tissues investigated. Preliminary findings suggest the eccrine gland secretory clear cell as the main source of fluid transport in hyperhidrosis.

Innervation and receptor profiles of the human apocrine (epitrichial) sweat gland: routes for intervention in bromhidrosis

Background  Human apocrine (epitrichial) sweat glands secrete in response to local or systemic administration of catecholamines and cholinergic agonists. As the process of secretion in human apocrine glands is not fully understood and no literature detailing the expression of adrenergic, cholinergic and purinergic receptors is available, there is a need to know the receptor types. Such data could provide new approaches for the treatment of axillary bromhidrosis.

Calcium-dependent regulation of membrane ion permeability in a cell line derived from the equine sweat gland epithelium

We measured the rates of 125I- and 86Rb+ efflux from preloaded, cultured equine sweat gland cells. The calcium ionophore ionomycin increased the efflux of both isotopes. Anion efflux was unaffected by Ba2+, but this cation inhibited 86Rb(+)-efflux, suggesting that [Ca2+]i-activated potassium channels were present. Activation of these channels was not, however, important for the efflux of anions. We measured 125I- efflux from valinomycin-depolarised cells in which anion cotransport was inhibited. Changes in 125I- efflux reflect changes in anion permeability under these conditions, and ionomycin caused a clear permeability increase that was abolished by the anion channel blocker diphenylamine-2-carboxylate. ATP and UTP increased the efflux of both isotopes, suggesting that type P2U purine receptors allow these nucleotides to regulate membrane permeability.

Activation of chloride secretion via proteinase-activated receptor 2 in a human eccrine sweat gland cell line – NCL-SG3

Abstract:  Proteinase‐activated receptor 2 (PAR‐2) has been shown to elicit secretion in a variety of secretory epithelial cells by the transepithelial movement of chloride ions across the apical membrane. However, it is not known whether these receptors are present and/or functional in the secretory epithelial cells of the human eccrine sweat gland. To investigate this possibility mRNA analysis, Ca2+ microspectrofluorimetry and the short circuit current (Isc) technique were used to quantify electrolyte transport in a cell line (NCL‐SG3) derived from human eccrine sweat gland secretory epithelia. The results provided molecular and functional evidence of the presence of PAR‐2 receptors in the NCL‐SG3 cells and show that these receptors can activate transepithelial Cl− secretion possibly via Ca2+‐activated Cl− channels.

Galanin is a modulator of eccrine sweat gland secretion

The neuropeptide galanin has been ascribed different roles in modulating physiological functions in the skin. The present study examined the function of galanin in eccrine sweat gland physiology. We demonstrated secretion of galanin by sweat glands in vivo by radioimmunoassay of human sweat (20–192 fmol galanin/ml). Furthermore, human sweat glands expressed galanin receptors GalR2 and GalR3. Using chamber short‐circuit current (Isc) measurements showed that application of galanin to human NCL‐SG3 cells led to a significant increase in Isc, which was inhibited by the presence of chloride channel blockers and in chloride‐free Krebs solution. Additionally, application of SNAP 37889, a non‐peptidergic selective antagonist of GalR3, abolished the effect of galanin on Isc. In summary, our results show that galanin can regulate transepithelial chloride ion transport and fluid secretion by stimulating GalR3 in NCL‐SG3 cells and demonstrate a possible important extraneural function of galanin in sweat gland physiology.

Localisation of the Vacuolar Proton Pump (V-H+-ATPase) and Carbonic Anhydrase II in the Human Eccrine Sweat Gland

The localisation of the vacuolar proton pump (V-H+-ATPase) and the enzyme carbonic anhydrase II (CAII) was investigated in the human eccrine sweat gland employing standard immunohistochemical techniques after antigen retrieval using microwave heat treatment and high pressure. The high-pressure antigen retrieval unmasked the presence of V-H+-ATPase in the clear cells of the secretory coil, with a distribution similar to that previously observed for CAII. However, the dark cells were unreactive to both antibodies. In addition, heat and high-pressure antigen retrieval demonstrated the presence of CAII in the apical zone of luminal cells of the reabsorptive duct, a location not previously reported. The localisation of V-H+-ATPase and CAII in the secretory coil clear cells suggests that (the) formation of HCO−3 and H+ by carbonic anhydrase II and the transport of H+ by V-H+-ATPase may play an role in sweat fluid secretion. Their presence at the apex of the duct cells indicates involvement in ductal ion reabsorption.

Vacuolar-type H+ -ATPase distribution in unstimulated and acetylcholine-activated isolated human eccrine sweat glands.

The presence and cellular distribution of subunits of the V1 sector of the vacuolar-type H+-ATPase (V-ATPase) was investigated in isolated human eccrine sweat glands. In every instance, V-ATPase was located in the cytoplasm and apical membranes of the luminal cells of the reabsorptive duct segment. In the secretory coil, both diffuse and perinuclear staining was demonstrated in the secretory cells, with additional expression at the apical and basolateral membranes and on the intercellular canaliculi. There was no detectable difference in V-ATPase expression as a result of prior application of 100 µM acetylcholine.