Metabolic component of the temperature-sensitivity of slow waves recorded from gastric muscle of the guinea-pig

Effects of different temperatures of carbohydrate-protein-containing drinks on gastric emptying rate after exercise in healthy young men: randomized crossover trial

Background

The present study examined the effects of different temperatures of carbohydrate-protein-containing drinks after exercise on the subsequent gastric emptying rate in healthy young men.

Methods

Twelve healthy young men completed two, 1-day trials in random order. In both trials, the participants completed intermittent cycling exercise for 20 min, consisting of a 120% heart rate peak for 20 s, followed by 25 W for 40 s. Participants consumed 400 mL of carbohydrate-protein-containing drink (0.85 MJ) at 4 °C (EX + 4 °C) or 60 °C (EX + 60 °C) over a 5-min period after exercise. The participants sat on a chair for 2.5 h to measure their gastric emptying rate using the ¹³C-sodium acetate breath test. Subjective feelings of gastrointestinal discomfort and appetite were measured using a visual analog scale. Interstitial fluid glucose levels after drinking were measured using a continuous glucose-monitoring device.

Results

The percentage excretion of ¹³CO₂ tended to be higher at EX + 60 °C than at EX + 4 °C from the start of the test until 30 min after drink ingestion (5.7 ± 0.5 vs. 6.5 ± 0.4%dose/h for the EX + 4 °C and EX + 60 °C trials, respectively; effect sizes [ES] = 0.277, p = 0.065). The time of maximum ¹³CO₂ emissions per hour (Tmax-calc) and the time of half ¹³CO₂ emissions per hour (T_1/2) did not differ between trials. Subjective gastrointestinal discomfort was lower at EX + 60 °C compared to EX + 4 °C (ES = 0.328, p = 0.041). There were no significant differences in interstitial fluid glucose levels between the different temperatures of carbohydrate-protein-containing drinks after exercise (p = 0.698).

Conclusions

Consumption of warm carbohydrate-protein-containing drinks after exercise may accelerate gastric emptying in the very early phase and may reduce gastric discomfort.

Trial registration

University Hospital Medical Information Network, UMIN000045626. Registered on June 10, 2021.

The effects of different temperatures of post-exercise protein-containing drink on gastric motility and energy intake in healthy young men

The present study examined the effects of different temperatures of protein-containing drink after exercise on subsequent gastric motility and energy intake in healthy young men. Twelve healthy young men completed three, 1-d trials in a random order. In all trials, the subjects ran on a treadmill for 30 min at 80% of maximum heart rate. In exercise + cold drink (2°C) and exercise + hot drink (60°C) trials, the subjects consumed 300 ml of protein-containing drink (0·34 MJ) at 2°C or 60°C over a 5-min period after exercise. In the exercise (i.e. no preload) trial, the subjects sat on a chair for 5 min after exercise. Then, the subjects sat on a chair for 30 min to measure their gastric motility with an ultrasound imaging system in all trials. Thereafter, the subjects consumed a test meal until they felt comfortably full. Energy intake in the exercise + hot drink trial was 14 % and 15 % higher than the exercise (P = 0·046, 95% CI 4·010, 482·538) trial and exercise + cold drink (P = 0·001, 95% CI 160·089, 517·111) trial, respectively. The frequency of the gastric contractions in the exercise + hot drink trial was higher than the exercise (P = 0·023) trial and exercise + cold drink (P = 0·007) trial. The total frequency of gastric contractions was positively related to energy intake (r = 0·386, P = 0·022). These findings demonstrate that consuming protein-containing drink after exercise at 60°C increases energy intake and that this increase may be related to the modulation of the gastric motility.

Expression and function of a T-type Ca2+ conductance in interstitial cells of Cajal of the murine small intestine

Interstitial cells of Cajal (ICC) generate slow waves in gastrointestinal (GI) muscles. Previous studies have suggested that slow wave generation and propagation depends on a voltage-dependent Ca(2+) entry mechanism with the signature of a T-type Ca(2+) conductance. We studied voltage-dependent inward currents in isolated ICC. ICC displayed two phases of inward current upon depolarization: a low voltage-activated inward current and a high voltage-activated current. The latter was of smaller current density and blocked by nicardipine. Ni(2+) (30 μM) or mibefradil (1 μM) blocked the low voltage-activated current. Replacement of extracellular Ca(2+) with Ba(2+) did not affect the current, suggesting that either charge carrier was equally permeable. Half-activation and half-inactivation occurred at -36 and -59 mV, respectively. Temperature sensitivity of the Ca(2+) current was also characterized. Increasing temperature (20-30°C) augmented peak current from -7 to -19 pA and decreased the activation time from 20.6 to 7.5 ms [temperature coefficient (Q10) = 3.0]. Molecular studies showed expression of Cacna1g (Cav3.1) and Cacna1h (Cav3.2) in ICC. The temperature dependence of slow waves in intact jejunal muscles of wild-type and Cacna1h(-/-) mice was tested. Reducing temperature decreased the upstroke velocity significantly. Upstroke velocity was also reduced in muscles of Cacna1h(-/-) mice, and Ni(2+) or reduced temperature had little effect on these muscles. Our data show that a T-type conductance is expressed and functional in ICC. With previous studies our data suggest that T-type current is required for entrainment of pacemaker activity within ICC and for active propagation of slow waves in ICC networks.

Factors which determine the duration of follower potentials in longitudinal smooth muscle isolated from the guinea-pig stomach antrum

In isolated longitudinal muscle tissues of the guinea-pig stomach antrum, recording electrical responses from smooth muscle cells revealed a periodical generation of follower potentials with variable durations. The I-D relationship, made by plotting the duration as a function of the interval before generating follower potential, was linear. Experiments were carried out to investigate the effects of chemicals which had been known to modulate the release of Ca(2+) from the internal stores (2-aminoethoxy-diphenyl-borate, cyclopiazonic acid, caffeine), inhibit mitochondrial metabolic activity (m-chlorophenyl hydrazone, 2-deoxy-D-glucose, potassium cyanide, rotenone), inhibit ATP-sensitive K-channels distributed in mitochondria (glibenclamide, 5-hydroxydecanoic acid) and inhibit the activity of proteinkinase C (chelerythrine), on the I-D relationship of follower potentials. The effects of depolarization on follower potentials were assessed by stimulating tissues with high potassium solution. Experiments were carried out mainly in the presence of nifedipine which minimized the movements of muscles with no modulation of follower potentials. Cycropiazonic acid and caffeine reduced the slope of I-D relationship, with associated reduction of the duration and frequency of follower potentials. 2-Aminoethoxydiphenyl borate reduced the duration and amplitude and increased the frequency of follower potentials, with depolarization of the membrane, and the effects were simulated by high potassium solution. m-Chlorophenyl hydrazone, potassium cyanide, 2-deoxy-D-glucose, rotenone, 5-hydroxydecanoic acid and glibenclamide reduced the slope of I-D relationship, with associated reduction of the frequency of follower potentials. Chelerythrine did not modulate the slope of I-D relationship, with reduced frequency of follower potentials. It seemed likely that the amount of Ca(2+) released from the internal stores and also mitochondrial function had causal relationship to the duration of pacemaker potentials, suggesting that internal Ca-stores and mitochondria are taking the central role for determining the duration of the pacemaker activity. Proteinkinase C did not seem to participate to the function of mitochondria and internal Ca(2+) stores.

Recent advances in studies of spontaneous activity in smooth muscle: ubiquitous pacemaker cells

The general and specific properties of pacemaker cells, including Kit-negative cells, that are distributed in gastrointestinal, urethral and uterine smooth muscle tissues, are discussed herein. In intestinal tissues, interstitial cells of Cajal (ICC) are heterogeneous in both their forms and roles. ICC distributed in the myenteric layer (ICC-MY) act as primary pacemaker cells for intestinal mechanical and electrical activity. ICC distributed in muscle bundles play a role as mediators of signals from autonomic nerves to smooth muscle cells. A group of ICC also appears to act as a stretch sensor. Intracellular Ca2+ dynamics play a crucial role in ICC-MY pacemaking; intracellular Ca2+ ([Ca2+](i)) oscillations periodically activate plasmalemmal Ca2+-activated ion channels, such as Ca2+-activated Cl(-) channels and/or non-selective cation channels, although the relative contributions of these channels are not defined. With respect to gut motility, both the ICC network and enteric nervous system, including excitatory and inhibitory enteric neurons, play an essential role in producing highly coordinated peristalsis.

Hypoxia differentially modulates the activity of pacemaker and smooth muscle cells in the guinea pig stomach antrum

Effects of hypoxic solution (O(2) tension, 161 +/- 11 mmHg) on electrical responses of the membrane (slow waves), intracellular Ca(2+)-responses measured by Fura-2 fluorescence (Ca-transients) and isometric mechanical responses (phasic contraction) were observed in circular smooth muscles isolated from the guinea-pig stomach antrum. In normoxic solution (O(2) tension, 362 +/- 28 mmHg), muscle cells generated slow waves spontaneously, and switching to hypoxic solution caused an increase in frequency and decrease in duration of slow waves, with no significant change in the resting membrane potential. Hypoxia also reduced the amplitude and duration and increased the frequency of Ca-transients. The increase in frequency of slow waves by hypoxia was prevented by cyclopiazonic acid (CPA) but not by carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), potassium cyanide (KCN) or low-Ca solution. The reduction by hypoxia of the duration of slow waves was prevented by CCCP or KCN but not by CPA or low-Ca solution. Hypoxia resulted in an increase in frequency and decrease in amplitude of phasic contractions, and the changes were prevented by CPA but not by CCCP. These results suggested that in antrum smooth muscle tissues, the increase in frequency of spontaneous activity by hypoxia is related to the enhanced function of the CPA-sensitive internal Ca-stores in pacemaker cells, while the inhibition in amplitude of phasic contractions by hypoxia may be mainly related to the decrease in Ca(2+) release from the CPA-sensitive internal stores in smooth muscle cells. It is concluded that in hypoxic solution, the function of internal Ca(2+) stores is enhanced in ICC-MY and is inhibited in smooth muscle cells in the guinea-pig stomach antrum.

Gastric emptying of liquid and solid meals at various temperatures: effect of meal temperature for gastric emptying

BACKGROUND

Patients with functional dyspepsia frequently show delayed gastric emptying, and dietary advice is frequently given for its improvement. If meal temperature influences gastric emptying, advice regarding the meal temperature may become a possible component of dietary therapy. However, little information exists concerning the thermal effect of meals on gastric emptying. The aim of this study was to determine the thermal effect of liquid and solid meals on gastric emptying.

METHODS

The gastric emptying of liquid and solid test meals was examined in healthy volunteers (liquid, n = 25, mean age = 35.7 +/- 9.6 years, male-to-female ratio = 22:3; solid, n = 25, mean age = 35.2 +/- 8.8 years, male-to-female ratio = 20:5). Gastric emptying after the ingestion of liquid or solid meals at three different temperatures (4, 37, and 60 degrees C) was investigated with the [(13)C]-labeled acetate breath test. The lag phase time (T (max-calc)) and the half-emptying time (T (1/2)) were calculated from the (13)CO(2) breath excretion curve as indices of gastric emptying.

RESULTS

The values of T (max-calc) at 60 degrees C with both the liquid and solid meals were significantly smaller than those at 37 degrees C (P < 0.05). However, there was no difference in the T (1/2) values. In the analysis of the percent excretion of (13)CO(2) in 1 h (% dose/h) data with the liquid meal test in the earlier phase within 30 min, significantly larger values were found at 60 degrees C than at the other temperatures. These findings suggest that a hot meal significantly accelerates gastric emptying.

CONCLUSIONS

Meal temperature may be considered as a component of dietary therapy for patients with functional dyspepsia.

Regional differences in the frequency of slow waves in smooth muscle of the guinea-pig stomach

The frequency of slow waves recorded from circular muscle bundles with attached longitudinal muscle (intact muscle) was compared with that of slow potentials recorded from isolated circular muscle bundles (isolated muscle) from the guinea-pig stomach. In intact muscle preparations, slow waves were generated in the corpus, antrum and pylorus with a higher frequency in the corpus (about 5 min(-1)) than the other regions (about 2 min(-1) in antrum, about 1.5 min(-1) in pylorus). The resting potential amplitude was graded across the stomach, at about -50 mV in the fundus, -60 mV in the corpus, -65 mV in the antrum and -70 mV in the pylorus. A similar distribution of resting membrane potential and slow potential frequency was also observed in isolated muscle bundles from the different regions. Caffeine (1 mM) abolished slow waves in some corpus preparations and inhibited the 2nd component of slow waves in the antrum and pylorus, and also abolished slow potentials in isolated muscle preparations from any region of the stomach. This suggests that myenteric interstitial cells of Cajal (ICC-MY) are heterogeneously distributed in the stomach (pylorus, antrum and part of the corpus regions), with a homogeneous distribution of muscular interstitial cells of Cajal (ICC-IM) within the circular muscle bundles. The frequency of slow potentials in smooth muscle isolated from any region of the stomach changed linearly in response to membrane potential changes produced by either current injection or high potassium solutions. The frequency of slow potentials after setting the membrane potential at -60 mV was larger in the corpus than the antrum, suggesting that the high frequency discharge of corpus muscle is produced by the low membrane potential and additional unidentified factors. We suggest that the regional difference in slow wave discharge is produced mainly by ICC-IM, and the role of ICC-MY may be little, if any.

Cellular mechanism of the voltage-dependent change in slow potentials generated in circular smooth muscle of the guinea-pig gastric corpus

The cellular mechanism of the voltage-dependent properties of slow potentials were investigated in single bundles of circular smooth muscle isolated from the gastric corpus of guinea-pig using conventional microelectrode recordings. Hyperpolarization of the membrane by current injection decreased the frequency and increased the amplitude of slow potentials linearly. At potentials negative of -80 mV, slow potential generation was abolished and a periodic generation of clustered unitary potentials was evident. Application of cyclopiazonic acid (CPA, 20 microM) or thapsigargin (1 microM; inhibitors of Ca(2+)-ATPase), carbonyl cyanide m-chlorophenyl hydrazone (CCCP, 0.1 microM; mitochondrial protonophore) or 2-aminoethoxydiphenyl borate (2-APB, 20 microM; inhibitor of IP(3) receptor-mediated Ca(2+) release) depolarized the membrane and reduced or inhibited the amplitude and frequency of slow potentials: repolarization of the membrane to the resting level by current injection resulted in a recovery of the amplitude of slow potentials in the presence of CPA or CCCP, but not 2-APB. The slow potentials abolished by thapsigargin did not recover upon membrane repolarization. The altered frequency of slow potentials by 2-APB, CPA or CCCP was not reversed by membrane repolarization to control potentials. Depolarization of the membrane by about 10 mV with high-potassium solution also reduced the amplitude and increased the frequency of slow potentials in a manner restored by repolarization to control potentials upon current injection, suggesting that membrane depolarization did not affect the voltage dependency of pacemaker activity. The results indicate that in corpus circular muscles the voltage dependency of the frequency and amplitude of slow potentials requires a functional Ca(2+) store and mitochondria.

Calcium-associated mechanisms in gut pacemaker activity

A considerable body of evidence has revealed that interstitial cells of Cajal (ICC), identified with c-Kit-immunoreactivity, act as gut pacemaker cells, with spontaneous Ca²⁺ activity in ICC as the probable primary mechanism. Namely, intracellular (cytosolic) Ca²⁺ oscillations in ICC periodically activate plasmalemmal Ca²⁺-dependent ion channels and thereby generate pacemaker potentials. This review will, thus, focus on Ca²⁺-associated mechanisms in ICC in the gastrointestinal (GI) tract, including auxiliary organs.

Factors modifying the frequency of spontaneous activity in gastric muscle

The cellular mechanisms that determine the frequency of spontaneous activity were investigated in gastric smooth muscles isolated from the guinea-pig. Intact antral muscle generated slow waves periodically; the interval between slow waves was decreased exponentially by depolarization of the membrane to reach a steady interval value of about 7 s. Isolated circular muscle bundles produced slow potentials spontaneously or were evoked by depolarizing current stimuli. Evoked slow potentials appeared in an all-or-none fashion, with a refractory period of approximately 2-3 s. Low concentrations of chemicals that modify intracellular signalling revealed that the refractory period was causally related to the activity of protein kinase C (PKC). Activation of PKC increased and inhibition of PKC activity decreased the frequency of slow potentials. Chemicals that inhibit mitochondrial functions reduced the frequency of slow waves. Inhibition of internal Ca(2+)-store activity decreased the amplitude, but not the frequency of slow potentials, suggesting that the amplitude is causally related to Ca(2+) release from the internal store. The results suggest that changes in [Ca(2+)](i) caused by the activity of mitochondria may play a key role in determining the frequency of spontaneous activity in gastric pacemaker cells.