Mixed effects of moderate exercise and subsequent various food ingestion on breath acetone.

Acetone, which is exhaled with breath, is a by-product of lipolysis and could be used as a simple, useful indicator of lipolysis in the body because, unlike blood sampling, it can be measured non-invasively and repeatedly. Breath acetone concentration, however, is known to be affected by several factors such as exercise and food. We designed the experiments to evaluate the mixed effect on breath acetone of exercise and food ingestion in order to enhance the usefulness of breath acetone for monitoring fat loss. Seven healthy males performed moderate exercise for twice of 45 min with an interval of 15 min then rested for 4 h. Exhaled air was sampled every 15 min throughout the experiment. The subjects took one of four types, sugar-rich, balanced, protein-rich and fat-rich, of food for lunch one hour after the exercises or kept fasting. In the case of fasting, breath acetone kept increasing significantly (p< 0.05) compared with the rest value after the exercises until the end of the experiment. In contrast, in the case of taking any type of food, the change in breath acetone varied according to the food type. In the case of taking sugar-rich food, breath acetone significantly decreased (p< 0.05) compared with the fasting case. This decrease might be due to a suppression of acetone production when carbohydrates such as sugar are supplied to a body in the fasting condition. In contrast, in the case of taking fat-rich food, breath acetone showed the higher level than the fasting case. This additional increase might be attributable to the promotion of ketone bodies production, including acetone, due to the ingestion of medium chain triglycerides contained in the fat-rich food. We should therefore consider exercise and food ingestion in using breath acetone as a non-invasive indicator of lipolysis.

Inhalation of molecular hydrogen increases breath acetone excretion during submaximal exercise: a randomized, single-blinded, placebo-controlled study.

Aerobic exercise is widely accepted as a beneficial option for reducing fat in humans. Recently, it has been suggested that molecular hydrogen (H2) augments mitochondrial oxidative phosphorylation. Therefore, the hypothesis that inhaling H2 could facilitate lipid metabolism during aerobic exercise was investigated in the current study by measuring the breath acetone levels, which could be used as non-invasive indicators of lipid metabolism. This study aimed to investigate the effect of inhaling H2 on breath acetone output during submaximal exercise using a randomized, single-blinded, placebo-controlled, and cross-over experimental design. After taking a 20-minute baseline measurement, breath acetone levels were measured in ten male subjects who performed a 60% peak oxygen uptake-intensity cycling exercise for 20 minutes while inhaling either 1% H2 or a control gas. In another experiment, six male subjects remained in a sitting position for 45 minutes while inhaling either 1% H2 or a control gas. H2 significantly augmented breath acetone and enhanced oxygen uptake during exercise (P < 0.01). However, it did not significantly change oxidative stress or antioxidant activity responses to exercise, nor did it significantly alter the breath acetone or oxygen uptake during prolonged resting states. These results suggest that inhaling H2 gas promotes an exercise-induced increase in hepatic lipid metabolism. The study was approved by the Ethical Committee of Chubu University, Japan (approved No. 260086-2) on March 29, 2018.

Breath isoprene excretion during rest and low-intensity cycling exercise is associated with skeletal muscle mass in healthy human subjects.

The physiological roles of isoprene, which is one of the many endogenous volatile organic compounds contained in exhaled breath, are not well understood. In recent years, exhaled isoprene has been associated with the skeletal muscle. Some studies have suggested that the skeletal muscle produces and/or stores some of the isoprene. However, the evidence supporting this association remains sparse and inconclusive. Furthermore, aging may affect breath isoprene response because of changes in the skeletal muscle quantity and quality. Therefore, we investigated the association between the breath isoprene excretion ([Formula: see text]) and skeletal muscle mass in young (n = 7) and old (n = 7) adults. The participants performed an 18 min cycling exercise after a 3 min rest. The workload corresponded to an intensity of 30% of the heart rate reserve, as calculated by the Karvonen formula. The exhaled breath of each participant was collected during the exercise test. We calculated [Formula: see text] from the product minute ventilation and isoprene concentration and, then, investigated the relationships between [Formula: see text] and muscle mass, which was measured by multi-frequency bioelectrical impedance analysis. Importantly, muscle mass persisted as a significant determinant that explained the variance in [Formula: see text] at rest even after adjusting for age. Furthermore, the muscle mass was a significant determinative factor for [Formula: see text] response during exercise, regardless of age. These data indicated that skeletal muscle mass could be one of the determinative factors for [Formula: see text] during rest and response to exercise. Thus, we suggest that the skeletal muscle may play an important role in generating and/or storing some of the endogenous isoprene. This new knowledge will help to better understand the physiological functions of isoprene in humans (Approval No. 20190079).

Bicarbonate-rich fluid secretion predicted by a computational model of guinea-pig pancreatic duct epithelium.

KEY POINTS: The ductal system of the pancreas secretes large volumes of alkaline fluid containing HCO3- concentrations as high as 140 mm during hormonal stimulation. A computational model has been constructed to explore the underlying ion transport mechanisms. Parameters were estimated by fitting the model to experimental data from guinea-pig pancreatic ducts. The model was readily able to secrete 140 mm HCO3- . Its capacity to do so was not dependent upon special properties of the cystic fibrosis transmembrane conductance regulator (CFTR) anion channels and solute carrier family 26 member A6 (SLC26A6) anion exchangers. We conclude that the main requirement for secreting high HCO3- concentrations is to minimize the secretion of Cl- ions. These findings help to clarify the mechanism responsible for pancreatic HCO3- secretion, a vital process that prevents the formation of protein plugs and viscous mucus in the ducts, which could otherwise lead to pancreatic disease. ABSTRACT: A computational model of guinea-pig pancreatic duct epithelium was developed to determine the transport mechanism by which HCO3- ions are secreted at concentrations in excess of 140 mm. Parameters defining the contributions of the individual ion channels and transporters were estimated by least-squares fitting of the model predictions to experimental data obtained from isolated ducts and intact pancreas under a range of experimental conditions. The effects of cAMP-stimulated secretion were well replicated by increasing the activities of the basolateral Na+ -HCO3- cotransporter (NBC1) and apical Cl- /HCO3- exchanger (solute carrier family 26 member A6; SLC26A6), increasing the basolateral K+ permeability and apical Cl- and HCO3- permeabilities (CFTR), and reducing the activity of the basolateral Cl- /HCO3- exchanger (anion exchanger 2; AE2). Under these conditions, the model secreted ∼140 mm HCO3- at a rate of ∼3 nl min-1  mm-2 , which is consistent with experimental observations. Alternative 1:2 and 1:1 stoichiometries for Cl- /HCO3- exchange via SLC26A6 at the apical membrane were able to support a HCO3- -rich secretion. Raising the HCO3- /Cl- permeability ratio of CFTR from 0.4 to 1.0 had little impact upon either the secreted HCO3- concentration or the volume flow. However, modelling showed that a reduction in basolateral AE2 activity by ∼80% was essential in minimizing the intracellular Cl- concentration following cAMP stimulation and thereby maximizing the secreted HCO3- concentration. The addition of a basolateral Na+ -K+ -2Cl- cotransporter (NKCC1), assumed to be present in rat and mouse ducts, raised intracellular Cl- and resulted in a lower secreted HCO3- concentration, as is characteristic of those species. We conclude therefore that minimizing the driving force for Cl- secretion is the main requirement for secreting 140 mm HCO3- .

Degree of exercise intensity during continuous chest compression in upper-body-trained individuals.

BACKGROUND: Although chest-compression-only cardiopulmonary resuscitation (CCO-CPR) is recommended for lay bystanders, fatigue is easily produced during CCO-CPR. If CCO-CPR can be performed at a lower intensity of exercise, higher resistance to fatigue is expected. Since chest compression is considered to be a submaximal upper body exercise in a steady rhythm and since the unit of load for chest compression is expressed as work rate, we investigated the possibility that peak work rate of the upper body determines the level of exercise intensity during CCO-CPR. METHODS: Twelve sedentary individuals (group Se), 11 rugby players (group R), and 11 swimmers (group Sw) performed 10-min CCO-CPR, and heart rate (HR) and rating of perceived exertion (RPE) were measured as indices of exercise intensity. Multiple linear regression analysis was carried out to assess potential relationships of upper body weight, peak lumbar extension force, peak work rate, and peak oxygen uptake recorded during arm-crank exercise with HR and RPE during CCO-CPR. RESULTS: Values of peak work rate during arm-crank exercise (Peak WR-AC) in group Se, group R, and group Sw were 108 ± 12, 139 ± 27, and 146 ± 24 watts, respectively. Values of the latter two groups were significantly higher than the value of group Se (group R, P < 0.01; group Sw, P < 0.001). HR during CCO-CPR increased with time, reaching 127.8 ± 17.6, 114.8 ± 16.5, and 118.1 ± 14.2 bpm at the 10th minute in group Se, group R, and group Sw, respectively. On the other hand, RPE during CCO-CPR increased with time, reaching 16.4 ± 1.4, 15.4 ± 1.7, and 13.9 ± 2.2 at the 10th minute in group Se, group R, and group Sw, respectively. Multiple linear regression analysis showed that only peak WR-AC affects both HR and RPE at the 10th minute of CCO-CPR (HR, r = -0.458; P < 0.01; RPE, r = -0.384, P < 0.05). CONCLUSIONS: The degree of exercise intensity during CCO-CPR is lower in individuals who have a higher peak work rate of the upper body.

Higher ventilatory responses during and after passive walking-like leg movement in older individuals.

BACKGROUND: Minute ventilation (V · E) during walking has been shown to be higher in older individuals than in young individuals, but the mechanisms underlying the higher ventilatory response is unclear. Central command and peripheral neural reflex are important neural control mechanisms underlying ventilatory response during exercise. Passive leg movement has been used to exclude the influence of central command due to the lack of voluntary activation of muscles. The aim of the present study was to compare the ventilatory response during and after passive walking-like leg movement (PWM) in young and older individuals. METHODS: Eight young subjects (20 ± 2 years) and seven older subjects (70 ± 1 years) participated in this study. Subjects spent 7 minutes in a quiet standing (QS) position. Thereafter, they performed 14-minute rhythmic PWM at 1 Hz and this was followed by 7 minutes of QS. RESULTS: V · E values during pre-PWM QS were calculated as 1-minute averages using data obtained between 5 and 6 minutes. V · E values at pre-PWM QS in the young and older groups were 8.4 ± 2.1 and 7.5 ± 1.2 l/minute, respectively. V · E values increased significantly at the first minute of PWM to 11.4 ± 2.2 and 10.4 ± 2.5 l/minute in the young and older groups, respectively (P <0.001). In the young group, V · E at the last minute of PWM (9.2 ± 2.0 l/minute) was not significantly different from that at pre-PWM QS due to a decline in V · E, whereas V · E at the last minute of PWM in the older group (9.4 ± 2.2 l/minute) was still significantly higher (P <0.01). On the other hand, V · E at the first minute of post-PWM QS (7.2 ± 1.8 l/minute) was significantly lower than that during pre-PWM QS in the young group (P <0.05) but not in the older group. CONCLUSIONS: Ventilatory response during and after PWM is higher in older individuals than in young individuals. This may be associated with a mechanism(s) other than central command. Our findings may explain part of the higher V · E response while walking in older individuals.

Suppression of cardiocirculatory responses to orthostatic stress by passive walking-like leg movement in healthy young men.

BACKGROUND: Although passive walking-like leg movement in the standing posture (PWM) has been used in the clinical field, the safety of PWM has not been fully determined despite the risks of orthostatic intolerance due to standing posture. The aim of the present study was to examine cardiocirculatory response during PWM in healthy young men. METHODS: The subjects (n = 13) spent 5 min in a sitting position and then 5 min in a quiet standing position to determine baseline levels. Thereafter, they underwent 25-min rhythmic PWM at 1 Hz while standing. In another bout, subjects experienced the same protocol except that they underwent 25-min quiet standing (QS) instead of 25-min PWM. Two subjects dropped out of the 25-min QS due to feeling of discomfort. Thus, data obtained in the remaining eleven subjects are presented. RESULTS: In the PWM trial, systolic arterial blood pressure (SAP) decreased from 112 ± 8 mmHg during the sitting baseline period to 107 ± 8 mmHg during the standing baseline period (p <0.05), while heart rate (HR) increased from 73 ± 9 bpm during the sitting baseline period to 84 ± 10 bpm during the standing baseline period (p <0.001). After the imposition of PWM, SAP increased from 107 ± 8 mmHg in the standing baseline period to 120 ± 6 mmHg (p <0.001), while HR decreased from 84 ± 10 bpm in the standing baseline period to 76 ± 9 bpm (p <0.05). In the QS trial, SAP, which had decreased during the standing baseline period compared to that during the sitting baseline period, remained lowered during the 25-min QS period, while HR, which had increased during the standing baseline period compared to that during the sitting baseline period, remained elevated during the 25-min QS period. In both bouts, HR showed almost mirror-image changes in the high-frequency component of HR variability, suggesting that the changes in HR were due to change in parasympathetic activation. Double product (HR × SAP), as a predictor of myocardial oxygen consumption, during the 25-min QS period tended to increase with time, but double product remained almost constant during the 25-min PWM period. CONCLUSIONS: The results suggest that PWM is effective for suppressing cardiocirculatory responses to orthostatic stress.

Deletion of Slc26a6 alters the stoichiometry of apical Cl-/HCO-3 exchange in mouse pancreatic duct.

To define the stoichiometry and molecular identity of the Cl(-)/HCO(3)(-) exchanger in the apical membrane of pancreatic duct cells, changes in luminal pH and volume were measured simultaneously in interlobular pancreatic ducts isolated from wild-type and Slc26a6-null mice. Transepithelial fluxes of HCO(3)(-) and Cl(-) were measured in the presence of anion gradients favoring rapid exchange of intracellular HCO(3)(-) with luminal Cl(-) in cAMP-stimulated ducts. The flux ratio of Cl(-) absorption/HCO(3)(-) secretion was ∼0.7 in wild-type ducts and ∼1.4 in Slc26a6(-/-) ducts where a different Cl(-)/HCO(3)(-) exchanger, most likely SLC26A3, was found to be active. Interactions between Cl(-)/HCO(3)(-) exchange and cystic fibrosis transmembrane conductance regulator (CFTR) in cAMP-stimulated ducts were examined by measuring the recovery of intracellular pH after alkali-loading by acetate prepulse. Hyperpolarization induced by luminal application of CFTRinh-172 enhanced HCO(3)(-) efflux across the apical membrane via SLC26A6 in wild-type ducts but significantly reduced HCO(3)(-) efflux in Slc26a6(-/-) ducts. In microperfused wild-type ducts, removal of luminal Cl(-), or luminal application of dihydro-4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid to inhibit SLC26A6, caused membrane hyperpolarization, which was abolished in Slc26a6(-/-) ducts. In conclusion, we have demonstrated that deletion of Slc26a6 alters the apparent stoichiometry of apical Cl(-)/HCO(3)(-) exchange in native pancreatic duct. Our results are consistent with SLC26A6 mediating 1:2 Cl(-)/HCO(3)(-) exchange, and the exchanger upregulated in its absence, most probably SLC26A3, mediating 2:1 exchange.

Structure and function of the pancreas in the polycystic kidney rat.

OBJECTIVES: Mutation in the Pkhd1 gene that encodes a ciliary protein, fibrocystin, causes multiple cysts in the kidneys and liver in the polycystic kidney (PCK) rat, a model for human autosomal recessive PCK disease. To clarify the role of primary cilia in the pancreatic duct, we examined the structure and function of the exocrine pancreas of PCK rats. METHODS: Pancreatic juice and bile were collected from anesthetized rats. Pancreatic ductal structure was analyzed by microdissection and immunohist0chemistry. RESULTS: Histologically pancreatic acini were apparently normal, and no cysts were detected in the pancreas. Larger pancreatic ducts were irregularly dilated with enhanced expression of AQP1 in epithelial cells. The pancreatic duct of PCK rats exhibited significantly (P < 0.05) higher distensibility than that of wild-type (WT) rat at a physiological luminal pressure (3 cm H2O). Pancreatic fluid secretion stimulated with a physiological dose of secretin (0.03 nmol/kg per hour) in PCK rats was significantly smaller than that in WT, but the differences were not significant at higher doses. The amylase responses to carbamylcholine were not different between PCK and WT rats. CONCLUSIONS: These findings suggest that fibrocystin/primary cilia-dependent mechanisms may play a role in the regulation of pancreatic ductal structure and fluid secretion.

High glucose inhibits HCO3(-) and fluid secretion in rat pancreatic ducts.

Cellular mechanisms underlying the impairment of pancreatic fluid and electrolyte secretion in diabetes were examined using interlobular ducts isolated from rat pancreas. Fluid secretion was assessed by monitoring changes in luminal volume. HCO3(-) uptake across the basolateral membrane was estimated from the recovery of intracellular pH following an acid load. Exposure to high glucose concentrations inhibited fluid secretion and reduced the rate of basolateral HCO3(-) uptake in secretin-stimulated ducts isolated from normal rats. In ducts isolated from streptozotocin-treated diabetic rats, fluid secretion and basolateral HCO3(-) uptake were also severely impaired but could be largely reversed by incubation in normal-glucose solutions. Sodium-dependent glucose cotransporter 1 (SGLT1), glucose transporter (GLUT)1, GLUT2, and GLUT8 transcripts were detected by reverse transcriptase polymerase chain reaction in isolated ducts. Raising the luminal glucose concentration in microperfused ducts caused a depolarization of the membrane potential, consistent with the presence of SGLT1 at the apical membrane. Unstimulated ducts filled with high-glucose solutions lost luminal fluid by a phlorizin-sensitive mechanism, indicating that pancreatic ducts are capable of active glucose reabsorption from the lumen via SGLT1. In ducts exposed to high glucose concentrations, continuous glucose diffusion to the lumen and active reabsorption via SGLT1 would lead to elevation of intracellular Na+ concentration and sustained depolarization of the apical membrane. These two factors would tend to inhibit the basolateral uptake and apical efflux of Cl(-) and HCO3(-) and could therefore account for the impaired fluid and electrolyte secretion that is observed in diabetes.

Breath hydrogen produced by ingestion of commercial hydrogen water and milk.

OBJECTIVE: To compare how and to what extent ingestion of hydrogen water and milk increase breath hydrogen in adults. METHODS: Five subjects without specific diseases, ingested distilled or hydrogen water and milk as a reference material that could increase breath hydrogen. Their end-alveolar breath hydrogen was measured. RESULTS: Ingestion of hydrogen water rapidly increased breath hydrogen to the maximal level of approximately 40 ppm 10-15 min after ingestion and thereafter rapidly decreased to the baseline level, whereas ingestion of the same amount of distilled water did not change breath hydrogen (p < 0.001). Ingestion of hydrogen water increased both hydrogen peaks and the area under the curve (AUC) of breath hydrogen in a dose-dependent manner. Ingestion of milk showed a delayed and sustained increase of breath hydrogen in subjects with milk intolerance for up to 540 min. Ingestion of hydrogen water produced breath hydrogen at AUC levels of 2 to 9 ppm hour, whereas milk increased breath hydrogen to AUC levels of 164 ppm hour for 540 min after drinking. CONCLUSION: Hydrogen water caused a rapid increase in breath hydrogen in a dose-dependent manner; however, the rise in breath hydrogen was not sustained compared with milk.

CFTR functions as a bicarbonate channel in pancreatic duct cells.

Pancreatic duct epithelium secretes a HCO(3)(-)-rich fluid by a mechanism dependent on cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane. However, the exact role of CFTR remains unclear. One possibility is that the HCO(3)(-) permeability of CFTR provides a pathway for apical HCO(3)(-) efflux during maximal secretion. We have therefore attempted to measure electrodiffusive fluxes of HCO(3)(-) induced by changes in membrane potential across the apical membrane of interlobular ducts isolated from the guinea pig pancreas. This was done by recording the changes in intracellular pH (pH(i)) that occurred in luminally perfused ducts when membrane potential was altered by manipulation of bath K(+) concentration. Apical HCO(3)(-) fluxes activated by cyclic AMP were independent of Cl(-) and luminal Na(+), and substantially inhibited by the CFTR blocker, CFTR(inh)-172. Furthermore, comparable HCO(3)(-) fluxes observed in ducts isolated from wild-type mice were absent in ducts from cystic fibrosis (Delta F) mice. To estimate the HCO(3)(-) permeability of the apical membrane under physiological conditions, guinea pig ducts were luminally perfused with a solution containing 125 mM HCO(3)(-) and 24 mM Cl(-) in the presence of 5% CO(2). From the changes in pH(i), membrane potential, and buffering capacity, the flux and electrochemical gradient of HCO(3)(-) across the apical membrane were determined and used to calculate the HCO(3)(-) permeability. Our estimate of approximately 0.1 microm sec(-1) for the apical HCO(3)(-) permeability of guinea pig duct cells under these conditions is close to the value required to account for observed rates of HCO(3)(-) secretion. This suggests that CFTR functions as a HCO(3)(-) channel in pancreatic duct cells, and that it provides a significant pathway for HCO(3)(-) transport across the apical membrane.

Effect of dietary turmeric on breath hydrogen.

Turmeric is widely used in Indian cuisine. The main constituents of turmeric are curcumin and its analogues, which are well-known antioxidant compounds. In the present study, we hypothesized that turmeric in curry might increase bowel motility and activate hydrogen-producing bacterial flora in the colon, thereby increasing the concentration of breath hydrogen. Eight healthy subjects fasted for 12 h and ingested curry and rice with or without turmeric (turmeric knockout curry). Breath-hydrogen concentrations were analyzed every 15 min for 6 h by gas chromatography with a semiconductor detector. Curry with turmeric significantly increased the area under the curve of breath hydrogen and shortened small-bowel transit time, compared with curry not containing turmeric. These results suggested that dietary turmeric activated bowel motility and carbohydrate colonic fermentation.

Glucose transport in interlobular ducts isolated from rat pancreas.

Pancreatic duct cells express Na(+)-dependent glucose transporter, SGLT1 and Na(+)-independent glucose transporters, GLUT1, GLUT2, and GLUT8. We examined transepithelial glucose transport by pancreatic duct. Interlobular ducts were isolated from rat pancreas. During overnight culture both ends of the duct segments sealed spontaneously. The lumen of the sealed duct was micropunctured and the luminal fluid was replaced by HEPES-buffered solution containing 10.0 mM or 44.4 mM glucose. The bath was perfused with HEPES-buffered solution at 37 degrees C containing 10.0 or 44.4 mM glucose. Transepithelial differences in osmolality were balanced with mannitol. Glucose transport across ductal epithelium was measured by monitoring changes in luminal volume. When the lumen was filled with 44.4 mM glucose, with either 10.0 or 44.4 mM glucose in the bath, the luminal volume decreased to 65 approximately 70% of the initial volume in 15 min. Luminally-injected phlorizin, an inhibitor of SGLT1, abolished the decrease in luminal volume. With 10.0 mM glucose in the lumen and 44.4 mM glucose in the bath, the luminal volume did not change significantly. Luminal application of phlorizin under identical condition led to an increase in luminal volume. The data suggest that both active and passive transport mechanisms of glucose are present in pancreatic ductal epithelium.

Apical Cl-/HCO3- exchanger stoichiometry in the modeling of HCO3- transport by pancreatic duct epithelium.

Pancreatic duct cells secrete a HCO(3)(-)-rich (approximately 140 mM) fluid. Using a computer model of the pancreatic duct, Sohma, et al. have demonstrated that the activity of a Cl(-)/HCO(3)(-) exchanger with a 1: 1 stoichiometry at the apical membrane would have to be suppressed in order to achieve such a HCO(3)(-)-rich secretion. Recently the apical exchanger in pancreatic ducts has been identified as SLC26A6 and this probably mediates most of Cl(-)-dependent HCO(3)(-) secretion across the apical membrane. SLC26A6 is reported to mediate electrogenic Cl(-)/2HCO(3)(-) exchange when expressed in Xenopus oocytes. To assess the implications of this 1: 2 stoichiometry for HCO(3)(-) secretion, we have reconstructed the Sohma model using MATLAB/Simulink. To do this we have formulated an expression for the turnover rate of Cl(-)/2HCO(3)(-) exchange using network thermodynamics and we have estimated the constants from published experimental data. Preliminary data suggest that the 1: 2 stoichiometry of SLC26A6 would favor HCO(3)(-) secretion at higher concentrations.

Effects of Slc26a6 deletion and CFTR inhibition on HCO3- secretion by mouse pancreatic duct.

Pancreatic duct epithelium secretes HCO(3)(-)-rich fluid, which is dependent on cystic fibrosis transmembrane conductance regulator (CFTR). HCO(3)(-) transport across the apical membrane is thought to be mediated by both SLC26A6 Cl(-)-HCO(3)(-) exchange and CFTR HCO(3)(-) conductance. In this study we examined the relative contribution and interaction of SLC26A6 and CFTR in apical HCO(3)(-) transport. Interlobular pancreatic ducts were isolated from slc26a6 null mice. Intracellular pH (pH(i)) was measured by BCECF microfluorometry. Duct cells were stimulated with forskolin and alkalinized by acetate pre-pulse in the presence of HCO(3)(-)-CO(2). Apical HCO(3)(-) secretion was estimated from the recovery rate of pH(i) from alkaline load. When the lumen was perfused with high-Cl(-) solution, the rate of apical HCO(3)(-) secretion was increased by luminal application of CFTRinh-172 in ducts from wild-type mice but it was decreased in ducts from slc26a6 -/- mice. This suggests that slc26a6 and CFTR compensate/compete with each other for apical HCO(3)(-) secretion with high Cl(-) in the lumen. With high HCO(3)(-) in the lumen, luminal CFTRinh-172 reduced the rate of apical HCO(3)(-) secretion in both wild-type and slc26a6 -/- ducts. This suggests that HCO(3)(-) conductance of CFTR mediates a significant portion of apical HCO(3)(-) secretion with high HCO(3)(-) in the lumen.

Identification of key residues that cause differential gallbladder response to PACAP and VIP in the guinea pig.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have opposite actions on the gallbladder; PACAP induces contraction, whereas VIP induces relaxation. Here, we have attempted to identify key residues responsible for their interactions with PACAP (PAC1) and VIP (VPAC) receptors in the guinea pig gallbladder. We synthesized PACAP-27/VIP hybrid peptides and compared their actions on isolated guinea pig gallbladder smooth muscle strips using isotonic transducers. [Ala4]- and [Val5]PACAP-27 were more potent than PACAP-27 in stimulating the gallbladder. In contrast, [Ala4, Val5]- and [Ala4, Val5, Asn9]PACAP-27 induced relaxation similarly to VIP. [Asn9]-, [Thr11]-, or [Leu13]PACAP-27 had 20-70% contractile activity of PACAP-27, whereas [Asn24,Ser25,Ile26]PACAP-27 showed no change in the activity. All VIP analogs, including [Gly4,Ile5,Ser9]VIP, induced relaxation. In the presence of a PAC1 receptor antagonist, PACAP(6-38), the contractile response to PACAP-27 was inhibited and relaxation became evident. RT-PCR analysis revealed abundant expressions of PAC1 receptor, "hop" splice variant, and VPAC1 and VPAC2 receptor mRNAs in the guinea pig gallbladder. In conclusion, PACAP-27 induces contraction of the gallbladder via PAC1/hop receptors. Gly4 and Ile5 are the key NH2-terminal residues of PACAP-27 that distinguish PAC1/hop receptors from VPAC1/VPAC2 receptors. However, both the NH2-terminal and alpha-helical regions of PACAP-27 are required for initiating gallbladder contraction.