Expression of aquaporin water channels in rat taste buds.

In order to gain insight into the molecular mechanisms that allow taste cells to respond to changes in their osmotic environment, we have used primarily immunocytochemical and molecular approaches to look for evidence of the presence of aquaporin-like water channels in taste cells. Labeling of isolated taste buds from the fungiform, foliate, and vallate papillae in rat tongue with antibodies against several of the aquaporins (AQPs) revealed the presence of AQP1, AQP2, and AQP5 in taste cells from these areas. AQP3 antibodies failed to label isolated taste buds from any of the papillae. There was an apparent difference in the regional localization of AQP labeling within the taste bud. Antibodies against AQP1 and AQP2 labeled predominantly the basolateral membrane, whereas the AQP5 label was clearly evident on both the apical and basolateral membranes of cells within the taste bud. Double labeling revealed that AQP1 and AQP2 labeled many, but not all, of the same taste cells. Similar double-labeling experiments with anti-AQP2 and anti-AQP5 clearly showed that AQP5 was expressed on or near the apical membranes whereas AQP2 was absent from this area. The presence of these 3 types of AQPs in taste buds but not in non-taste bud-containing epithelia was confirmed using reverse transcription-polymerase chain reaction. Experiments using patch clamp recording showed that the AQP inhibitor, tetraethylammonium, significantly reduced hypoosmotic-induced currents in rat taste cells. We hypothesize that the AQPs may play roles both in the water movement underlying compensatory mechanisms for changes in extracellular osmolarity and, in the case of AQP5 in particular, in the gustatory response to water.

Fatty acid responses in taste cells from obesity-prone and -resistant rats.

One of the transduction mechanisms for the chemoreception of fat has been proposed to involve the inhibition of delayed rectifying potassium (DRK) channels by polyunsaturated free fatty acids (PUFAs). In the present study we have compared the responsiveness of fungiform taste receptor cells (TRCs) to fatty acids in obesity-prone (Osborne-Mendel; O-M) and obesity-resistant (S5B/Pl) rat strains using patch clamp recording. TRCs from S5B/Pl rats were markedly more responsive to PUFAs than those from O-M, yet with identical inhibition constants. Moreover, addition of PUFAs to subthreshold concentrations of saccharin enhanced preference for the mixture in two-bottle preference tests compared to the saccharin alone in S5B/Pl but not O-M rats. The correlation between electrophysiological and behavioral effects of PUFAs suggested that differences in fatty acid-sensitive DRK expression may underlie the phenotypic differences between S5B/Pl and O-M rats. Consistent with this hypothesis, O-M rats exhibit a greater DRK current density and express quantitatively more DRK channels as assayed using quantitative real-time PCR. No differences were found when comparing expression of fatty acid activated two pore domain potassium channels. We propose that the ratio of fatty acid-sensitive DRK channels to fatty acid-insensitive DRK channels may be important to contributing to overall peripheral fatty acid sensitivity and in that way influence the strength of the resulting chemosensory response to fat.

Water turnover and changes in body composition during arduous wildfire suppression.

INTRODUCTION: Our lab has recently documented the total energy expenditure during arduous wildfire suppression using the doubly labeled water methodology. The elevated rates of isotopic elimination indicate an arduous working environment that may often compromise energy balance and overall hydration. PURPOSE: The purpose of this investigation was to determine the effects of arduous wildfire suppression on water turnover and changes in body composition in wildland firefighters (WLFF). METHODS: WLFF (N = 14) were studied during a 5-d period of arduous fire suppression work. A comparison group (N = 13) of recreationally active college students (RACS) was also studied. Water turnover was measured from rates of 2H elimination (rH2O). Urine osmolality, specific gravity, and skinfold measures were also collected. RESULTS: WLFF demonstrated a decrease in nude body weight (pre = 71.9 +/- 10.4 kg, post = 70.9 +/- 10.2 kg, P = 0.0001) and total body water (pre = 42.9 +/- 7.2 kg, post = 42.0 +/- 6.7 kg, P = 0.0046). RACS maintained total body water and body weight during the experimental period. Isotope (2H2O) dilution demonstrated that rH2O was significantly higher for the WLFF (rH2O = 6.7 +/- 1.4 and 3.8 +/- 1.0 L.24 h-1 for the WLFF and RACS, respectively). CONCLUSION: These results demonstrate an arduous work environment that threatens hydration, energy balance, and perhaps normal glycogen status.

Total energy expenditure during arduous wildfire suppression.

PURPOSE: The purpose of this investigation was to determine the total energy expenditure (TEE) by using the doubly labeled water (DLW) methodology during 5 d of wildfire suppression in Montana, California, Florida, Washington, and Idaho. METHODS: Seventeen wildland firefighters (from three Interagency Hot Shot crews, N = 8 men, height = 177 +/- 7 cm, weight = 74.6 +/- 6.4 kg, age = 24.5 +/- 1.8 yr; N = 9 women, height = 170 +/- 7 cm, weight = 65.2 +/- 8.0 kg, age = 25.0 +/- 1.3 yr) served as subjects. Before wildland fire suppression, each subject was given an oral dose of 2H2O and H218O (approximately 0.23 g 2H2O.kg estimated TBW-1 and 0.39 g H218O.kg estimated TBW-1). Urine samples were collected between 0400 and 0600 daily. TEE was calculated using the two-point method for days 1-3 and 1-5, with the TEE for days 4-5 calculated by extrapolation. Urine samples from other crew members not participating in the DLW protocol were collected at the same times and used to adjust calculations of isotopic elimination for background shifts. RESULTS: TEE was 17.4 +/- 3.7 and 17.5 +/- 6.9 MJ.d-1 during days 1-3 and 4-5, respectively. The energy expenditure associated with physical activity (EEA) was 8.8 +/- 3.0 and 8.9 +/- 6.1 MJ.d-1 for days 1-3 and 4-5, respectively. CONCLUSION: The current data demonstrate consistently high daily energy expenditure in the wildland firefighter. These data also demonstrate that the doubly labeled water methodology is an appropriate methodology for the measure of TEE during unpredictable field operations if adjustments are made for changes in background enrichment and elevated water turnover.