The purpose of this study was twofold: (i) to investigate if sprint-interval training (SIT) alters myosin heavy chain (MyHC) isoform composition and bioenergetic properties within the rat diaphragm, and (ii) to determine if mild normobaric hypoxia would enhance the effects of SIT-induced diaphragmatic adaptation. Male Wistar rats (8 weeks old) were randomly assigned to one of four groups (n = 7/group): (i) normoxic control (NC); (ii) normoxic training (NT); (iii) hypoxic control (HC); or (iv) hypoxic training (HT). The NT and HT groups were engaged in SIT (1 min sprint and 2–5 min rest, 6–10 sets/day, 5–6 days/week) on a treadmill for 9 weeks. Animals in the HC and HT groups were exposed to normobaric hypoxia (14.5% O2) during an SIT program from the 4th week of the training period. After completion of the training program, MyHC composition, citrate synthase (CS) activity, and lactate dehydrogenase (LDH) activity in the diaphragm and plantaris muscle were analyzed. An analysis of diaphragmatic MyHC composition demonstrated increased type IIa and decreased type IId/x for both training groups (P < 0.05), with the HT group producing greater changes than the NT group (P < 0.05). The plantaris muscle, however, showed increased Type IIa and IId/x and decreased Type IIb for both the NT and HT groups (P < 0.05). CS activity increased only for the training groups (P < 0.05), and this change was greater for the HT group in the diaphragm and for the NT group in the plantaris muscle (P < 0.05). Further, diaphragmatic LDH activity in HT was significantly lower (P < 0.05) than in HC and NT. These findings demonstrated that SIT could induce alterations in MyHC composition from fast to slow within type II isoforms and also improve the oxidative capacity in the diaphragm and plantaris muscles. It is of importance that our data revealed that SIT-induced diaphragmatic adaptations were enhanced when SIT was performed in normobaric hypoxia.
To determine if vasoactive intestinal peptide (VIP) restores neural activity from tetrodotoxin (TTX) blockade, we studied the effects of VIP and related agents on carbachol (Cch)-induced Cl− secretion in control-isolated guinea pig distal colon and in that treated with TTX. The short circuit current (Isc) increased dose-dependently after serosal applications of Cch (10−6–2 × 10−5 M) and VIP (5 × 10−9–10−7 M). But no additive or synergistic increase in Isc was observed. Cch- and VIP-induced Isc was completely abolished by a serosal application of TTX (10−6 M). However, a serosal application, not mucosal, of VIP (10−7 M) and 8-bromo-cAMP (10−3 M) restored the Cch-stimulated, TTX-inhibited Isc by 113% and 75.8%, respectively. Furthermore, mucosal and serosal applications of forskolin (aden late cyclase activator) restored the Isc by 43.9% and 65.3%, respectively. The restored Isc was completely abolished by atropine (muscarinic receptor antagonist). These results suggest that VIP may restore the cholinergic activity by increasing the level of intracellular cAMP, and that cholinergic neuron is very likely to be responsible for the regulation of Cl− secretion at neuroepithelial junctions. The exact mechanism of VIP's effect on the TTX-inhibited epithelial Cl− secretion, and its possible usefulness in the treatment of TTX-induced pathophysiological conditions, remain to be determined.
The present study investigated the underlying cellular mechanism in the effect of ligustrazine (tetramethylpyrazine, TMP) on the anion secretion of colonic mucosa in rats using a short-circuit current (Isc) technique in conjunction with “tool drugs.” (i) After a pretreatment of the tissues by bathing the bilateral surface with Cl−-free Krebs-Henseleit (K-H) solution for over an hour, a basolateral application of 1 mmol/l TMP produced an increase in Isc, and the total charges transported for 30 min were about 8.7 ± 1.4 mC/cm2; an apical pretreatment of DPC and a basolateral addition of acetazolamide decreased the TMP-induced Isc by about 60% (P < 0.01) and 45% (P < 0.05), respectively; a basolateral application of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), the inhibitor of Na+-HCO3− cotransporter (NBC), did not alter the TMP-induced Isc. (ii) After the bilateral surface of mucosa was bathed with HCO3−-free K-H solution for over an hour, a basolateral application of 1 mmol/l TMP produced an increase in Isc, and the total charges transported in 30 min were about 8.3 ± 1.9 mC/cm2; an apical pretreatment of DPC (1 mmol/l), the inhibitor of Cl− channels, decreased the TMP-induced Isc by about 84% (P < 0.01). The basolateral presence of bumetanide (0.1 mmol/l), the inhibitor of Na+-K+-Cl− cotransporter (NKCC), significantly reduced the TMP-evoked Isc by about 86% (P < 0.01). In conclusion, (i) ligustrazine could promote colonic mucosa secretion Cl− via apical Cl− channels and basolateral NKCC; (ii) ligustrazine could promote colonic mucosa secretion HCO3− via apical Cl− channels and the basolateral diffusion of CO2.
Short-chain fatty acids, such as propionate and acetate, are produced by a bacterial fermentation of carbohydrates in the colonic lumen. We examined the effects of propionate on the frequency and mean amplitude of spontaneous giant contractions (GCs) in circular muscle strips of the rat distal colon with the mucosa attached. An addition of propionate increased the frequency of GCs for about 20 min (≥1 mm), but the mean amplitude was decreased (≥0.1 mm). The propionate-induced increase in the frequency of GCs was blocked by the muscarinic acetylcholine receptor antagonist, atropine. In contrast, the nicotinic receptor antagonist, hexamethonium, augmented the response. The propionate-induced decrease in the mean amplitude of GCs was prevented by the cyclooxygenase inhibitor, piroxicam. A pretreatment of the tissues with acetate prevented the propionate-induced modulations of the frequency and amplitude of GCs. These results suggest that propionate increases the frequency of GCs by an activation of cholinergic motor neurons and decreases the mean amplitude by a prostaglandin release. Propionate as well as acetate may be involved in the regulation of spontaneous circular muscle activity in the rat distal colon.
Electroacupuncture (EA) was applied bilaterally to the acupoints of Zu-san-li (ST-36) and Kun-lun (BL-60) in the hindlimbs of mice. The therapeutic effect of EA on inflammatory pain induced by an ipsilateral injection of complete Freund's adjuvant (CFA) into the right paw of the mouse was investigated in this study. The time of paw-withdrawal latency (PWL) was used as an indicator for judging the intensity of the pain induced by the CFA injection. The EA effects were divided into immediate (PWL tests within 2 h after EA treatment) and cumulative (PWL tests during and after repetitive EA treatments for 3 weeks) effects. As immediate effects, PWL was significantly shortened in the CFA-injected paw, but was again prolonged 20 min after an EA treatment and lasted until 30 min after. As cumulative effects, PWL was significantly shortened in the CFA-injected paw, but recovered from the 2nd to the 8th day during repetitive EA treatments. No such effects could be observed after sham EA treatment, which resulted in behavior similar to that in untreated animals. These results demonstrate that the CFA-induced inflammatory pain in mice is an ideal model system for the investigation of EA effects and may serve as a valuable reference for the clinical treatment of inflammatory pain in human beings. Furthermore, the mouse pain model opens the possibility to apply the investigation also to transgenic mice.
Partner preference and paced mating tests were accomplished in ovariectomized female rats following bilateral radiofrequency lesions in the medial amygdala. Open field behavior and passive avoidance learning were also examined to investigate the underlying behavioral mechanism. Partner preference was determined in a chamber located between castrated and sexually active males. Airborne olfactory cues were presented to the female through small holes on the partition. The lesion diminished preference for the odor of sexually active males over that of castrated males, even after injection with a high-dose of estrogen. On the other hand, in a paced mating test the lesioned females without estrogen treatment showed a significantly shorter latency for entering the male's compartment in a two-compartment apparatus, which allowed the females, but not the males, to cross the barrier through a narrow opening at the bottom. However, an administration of estrogen and progesterone reduced the effect. The lesion had no effect on emotionality or exploratory behavior in an open field test, but it impaired passive avoidance learning capability. We suggest that a male poses an inherent threat to a female. The seemingly incompatible results of partner preference and paced mating tests can be compromised if the male is inherently aversive to the female; this emotional response can be removed by the medial amygdala lesion.
A general formula (Oka and Azuma's equation) has been rigorously derived for the circumferential wall tension in a hollow cylindrical tube in equilibrium. To evaluate the validity and usefulness of Oka and Azuma's equation, T = P1 × r1 − P2 × r2 (T, circumferential wall tension; P1 and P2, internal and external pressures of the tube; r1 and r2, the corresponding internal and external radii), we experimentally investigated changes in circumferential wall tension of noninjured (control) and injured dog common carotid arteries by using a newly developed apparatus with a photo- and X-ray-sensitive image sensor. We also studied histological features of the control and injured arteries with special reference to the relation of biomechanical properties. Two types of animal models with injured arteries—balloon-induced neointima or external collar-induced intimal thickening—were adopted in the present study. In the control arteries, the circumferential wall tension was experimentally confirmed to change from negative to positive by an increase in intraluminal pressure ranging from 50 to 180 mmHg. The critical intraluminal pressure that produced 0 dyne/cm of the circumferential wall tension was around 135 mmHg. The activation of arterial smooth muscles caused a significant increase in the critical pressure in the control arteries. In the arteries injured by neointima, the critical intraluminal pressure was significantly lower than that in the control. The activation of smooth muscles also significantly increased the critical pressure in the injured arteries. Histological examination demonstrated the existence of a circumferential neointimal formation along with a shortening of the internal diameter. In other arteries injured by intimal thickening, the circumferential wall tension was always negative at intraluminal pressure ranging from 50 to 180 mmHg. Newly developed structures consisted of elastic and collagen fibers, smooth muscles, and extracellular matrix in the intima and media of the injured arteries. These experimental findings suggest that the circumferential wall tension of dog common carotid arteries has been confirmed experimentally to become negative. We have also concluded that circumferential wall tension calculated with Oka-Azuma's equation may be one of the best parameters for evaluating changes in the biomechanical and histological properties of pathologically injured arteries.
We describe a unique method for establishing a functionally intact macula densa cell line from immortalized renal cells in culture. The macula densa is involved in the tubuloglomerular feedback (TGF) system in the kidney and specifically expresses neuronal nitric oxide synthase (nNOS). A 347 bp portion of the nNOS promoter was used to drive the expression of enhanced green fluorescence protein (EGFP). An immortalized distal tubule (DT) cell line was derived from distal tubules microdissected from the kidneys of SV40 large T antigen transgenic mice. Immunofluorescence labeling using an antibody against nNOS revealed no specific EGFP expression in immunofluorescence-negative DT cells. The established cell line (NE-MD) showed a time-dependent increase in signals of the nNOS protein when they were incubated with 12 µM furosemide (an inhibitor of Na+-K+-2Cl− symporter) for 5 h. In conclusion, this newly developed macula densa cell line will be useful in studies of the TGF stem.
To explore the possible role of the thin filament-linked regulation of cross-bridge cycling in living smooth muscle contraction, we studied the effects of TnIp and HSP20p, a synthetic peptide originating from an actin tropomyosin binding region of rabbit cardiac troponin I (residues 136–147; GKFKRPTLRRVR), and that of human heat shock protein 20 (residues 110–121; GFVAREFHRRYR) on the relaxation of skinned (cell membrane permeabilized) preparations from guinea pig taenia caeci. An active stress of the skinned preparations, resulting from actin–myosin interaction, rapidly decayed following Ca2+ removal (relaxation). TnIp accelerated the initial rapid phase and slowed the following slow phase of the relaxation. On the other hand, HSP20p only slowed the whole process of the relaxation. The relaxation time courses were well fitted in a double exponential manner, and the double exponential decay of the stress could be explained as a portion of fast-detaching cross bridges not to dissociate rapidly by Ca2+ removal, but to transfer to latch bridges dissociating very slowly. Our present results suggested that (i) TnIp and HSP20p accelerated transferring from fast-detaching cross bridges to slow-detaching (latch) bridges, and (ii) TnIp accelerated dissociation of the fast-detaching cross bridges and the latch bridges, while HSP20p slowed dissociation the fast-detaching cross bridges. Since TnIp and HSP20p are thought to bind to actin and tropomyosin, but not to myosin, we concluded that through thin-filament-dependent mechanisms these peptides regulated the formation and/or deformation of latch bridges in smooth muscle. The thin-filament-dependent regulation might physiologically control the stress maintenance and relaxation in smooth muscle cells.
It is controversial whether the ClC-3 protein, which is one of the voltage-dependent chloride channel ClC family members, is a candidate for the volume-sensitive outwardly rectifying (VSOR) Cl− channel per se or its regulator. Here, for the first time, we examined the single-channel properties of the VSOR Cl− channel in ventricular myocytes isolated from ClC-3–deficient mice. The single-channel current induced by cell swelling exhibited Cl− selectivity, mild outward rectification, and an intermediate unitary conductance (around 38 pS). A Cl− channel blocker, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), reversibly inhibited the outward current. These single-channel properties were identical with those in ClC-3 expressing wild-type ventricular myocytes. These results indicate that the single-channel activity of the VSOR Cl− channel is independent of the expression of ClC-3 proteins in mouse ventricular myocytes.
Lactate and H+ are suggested to promote the sickling process in red blood cells (RBCs) containing hemoglobin S. We demonstrated greater activity of the RBC monocarboxylate cotransporter MCT-1, lower RBC deformability and impaired hematological indices in sickle cell trait (SCT) carriers compared to control subjects, suggesting an involvement of MCT-1 in hemorheological disturbances in SCT carriers.
The wavelength dependence of optical action potentials was studied using voltage-sensitive merocyanine-rhodanine, merocyanine-oxazolone, and oxonol dyes in the isolated rat atrium preparation. Most of the dyes had action spectra that were similar to those reported in other pre-parations. Species-to-species difference was observed with a merocyanine-oxazolone dye.
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