In this study, we sought to investigate the effect of dendroaspis natriuretic peptide (DNP) on calcium-activated potassium current (I_K(Ca)) and its mechanism in gastric antral circular smooth muscle cells (SMCs) using the whole-cell patch-clamp technique. DNP concentration-dependently increased macroscopic I_K(Ca) and spontaneous transient outward currents (STOCs) in freshly isolated guinea pig gastric antral circular SMCs. The effects of DNP on I_K(Ca) and/or STOCs were not blocked by applying calcium-free bath solution or the ryanodine receptor (RyR) antagonist ryanodine (10 μM), but they were inhibited by the inositol triphosphate receptor (IP₃R) inhibitor heparin or the guanylate cyclase inhibitor LY83583. Moreover, a DNP-induced increase in STOCs was potentiated by the cyclic guanosine monophosphate (cGMP)–sensitive phosphoesterase inhibitor zaprinast. In conclusion, our results suggest that DNP increases I_K(Ca) in gastric antral circular SMCs by increasing cGMP production and activating IP₃Rs.

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This study examined acute hormone and recovery responses to resistance exercise with slow movements. Six men performed three types of exercise regimens (five sets of knee extension exercise): (1) high-intensity resistance exercise with normal movement (HN; 1 s for lifting action, 1 s for lowering action), (2) low-intensity resistance exercise with slow movement (LS; 3 s for lifting action, 3 s for lowering action), and (3) low-intensity resistance exercise with normal movement (LN; 1 s for lifting action, 1 s for lowering action). The intensity in the first set was set at approximately 80% of 1RM for HN and 40% of 1RM for LS and LN. In the HN and LS, the subjects performed each exercise set until exhaustion. In the LN, both intensity and number of repetitions were matched with those for LS. The total work volume in the HN showed approximately double the value of LS and LN (P < 0.05). Electromyography (EMG) data indicated that LS showed sustained EMG signals throughout the exercise. During the exercise, the HN and LS showed lower muscle oxygenation levels. After the exercise, LS caused significantly greater norepinephrine and free testosterone responses (delta value) than in the HN and LN (P < 0.05). However, no significant difference was observed in the recovery of maximal isometric strength, isokinetic strength, and jump performance between the HN and LS. These results indicate that slow movements during the resistance exercise are important for the enhancement of hormonal responses, especially catecholamine and free testosterone, but they do not affect muscle strength recovery.

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To understand the pathophysiology of hereditary cardiomyopathy, we measured the phosphorylation status of regulatory proteins, troponin I (TnI), troponin T (TnT), myosin light chain 2 (MLC2), and myosin-binding protein C (MyBP-C), and the Ca²⁺-dependence of tension development and ATPase activity in skinned right ventricular trabeculae obtained from cardiomyopathic (TO-2 strain, n = 8) and control (F1B strain, n = 8) hamsters. The Ca²⁺ sensitivities of tension development and ATPase activity (mean ± SD) were significantly (P < 0.0001) higher in the TO-2 strain (pCa₅₀ 5.64 ± 0.04 in tension and 5.65 ± 0.04 in ATPase activity) than in the F1B strain (pCa₅₀ 5.48 ± 0.03 in tension and 5.51 ± 0.03 in ATPase activity). No significant differences in their maximum values were observed between TO-2 (40.8 ± 7.4 mN/mm² in tension and 0.52 ± 0.15 μmol/l/s in ATP consumption) and F1B (42.3 ± 8.5 mN/mm² in tension and 0.58 ± 0.41 μmol/l/s in ATP consumption) preparations, indicating that the tension cost (ATPase activity/tension development) in TO-2 was quite similar to that in F1B. The phosphorylation levels of MLC2 and TnI were significantly (P < 0.01) lower in TO-2 than in F1B. These results suggest that the increase in the Ca²⁺ sensitivities of tension development and the ATPase activity in TO-2 hearts result from the decreased basal level of TnI phosphorylation, and these features can be considered to produce the incomplete diastolic relaxation and partly improve the systolic function in TO-2 hearts.

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Gonadotropin-releasing hormone (GnRH) neurons form the final common pathway for the central regulation of reproduction. As in other neurons, the discharge pattern of action potentials is important for these neurons to function properly. Therefore it is important to elucidate the expression patterns of various types of ion channels in these neurons because they determine cell excitability. To date, voltage-gated Ca²⁺ channels and SK channels have been reported to be expressed in rat GnRH neurons. In this study, we focused on K⁺ channels and analyzed their expression in primary cultured GnRH neurons, prepared from GnRH-EGFP transgenic rats, by means of perforated patch-clamp recordings. GnRH neurons exhibited delayed-rectifier K⁺ currents and large conductance voltage- and Ca²⁺-activated K⁺ (BK) currents. Moreover, multicell RT-PCR (reverse transcriptase–polymerase chain reaction) experiments revealed the expression of BK channel mRNAs (α, β1, β2, and β4). The results show the presence of delayed-rectifier K⁺ currents and BK currents besides previously reported slow afterhyperpolarization currents. These currents control the action potential repolarization and probably also the firing pattern, thereby regulating the cell excitability of GnRH neurons.

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We examined whether acupuncture can reduce both the incidence of seizures and hippocampal cell death using a mouse model of kainic acid (KA)–induced epilepsy. ICR mice were given acupuncture once a day at acupoint HT8 (sobu) bilaterally during 2 days before KA injection. After an intracerebroventricular injection of 0.1 μg of KA, acupuncture treatment was subsequently administered once more (total 3 times), and the degree of seizure was observed for 20 min. Three hours after injection, the survival of neuronal cells and the expressions of c-Fos, c-Jun, and glutamate decarboxylase (GAD)-67 in the CA1 and CA3 were determined using immunohistochemistry and Western blotting techniques. Acupuncture reduced the severity of the KA-induced epileptic seizure and the rate of neural cell death, and it also decreased the expressions of c-Fos and c-Jun induced by KA in the hippocampus. Furthermore, acupuncture increased GAD-67 expressions in the same areas. These results demonstrated that it could inhibit the KA-induced epileptic seizure and hippocampal cell death by increasing GAD-67 expressions.

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High physiological prolactin (PRL) stimulated intestinal calcium absorption and renal calcium uptake in mammals. Previous histomorphometric study revealed a significant increase in bone turnover in the trabecular part of the PRL-exposed long (cortical) bone; however, whole-bone densitometric analysis was unable to demonstrate such effect. We therefore studied differential changes in bone mineral density (BMD) and contents (BMC) of the femoral diaphysis and metaphysis in adult female rats exposed to high PRL induced by anterior pituitary (AP) transplantation. The estrogen-dependent effects of PRL on the femur were also investigated. We found that chronic exposure to PRL had no effect on BMD or BMC of the femoral diaphysis, which represented the cortical part of the long bone. It is interesting that 7 weeks after an AP transplantation, BMD and BMC of the femoral metaphysis were significantly decreased by 8% and 14%, respectively. Ovariectomy (Ovx) for 2, 5, and 7 weeks also decreased BMD and BMC in the femoral metaphysis, but not in the diaphysis. However, the AP transplantation plus Ovx (AP+Ovx) produced no additive effects. Nevertheless, 2.5 μg/kg 17β-estradiol (E2) supplementation abolished the osteopenic effects of both Ovx and AP+Ovx on the femur. As for the L5–6 vertebrae, BMD and BMC were not affected by PRL exposure, but were significantly decreased by Ovx and AP+Ovx, and such decreases were completely prevented by E2 supplementation. It could be concluded that high physiological PRL induced a significant osteopenia in the trabecular part, i.e., the metaphysis, of the femora of adult female rats in an estrogen-dependent manner. Since PRL had no detectable effect on the vertebrae, the effects of PRL on bone appeared to be site-specific.

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Methods of contemporary physics are increasingly important for biomedical research. For a multitude of diverse reasons there exists a gap between the practitioners of biomedicine and modern physics methodologies. In this work, the technique of surrogate data has been used as a method to test for the linearity or nonlinearity of biomedical functional near-infrared spectroscopy (fNIRS) signals observing brain activities. Throughout three different surrogate tests, the third-order autocovariance, the asymmetry resulting from time reversal, and the delay vector variance, the dynamic response of brain activities through fNIRS biomedical signals is very likely to be a nonlinear system.

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Positive chronotropy induced by β1-adrenergic stimulation is achieved by multiple interactions of ion channels and transporters in sinoatrial node pacemaker cells (SANs). To investigate the ionic mechanisms, we updated our SAN model developed in 2003 and incorporated the β1-adrenergic signaling cascade developed by Kuzumoto et al. (2007). Since the slow component of the delayed rectifier K⁺ current (I_Ks) is one of the major targets of the β1-adrenergic cascade, we developed a guinea pig model with a large I_Ks. The new model provided a good representation of the experimental characteristics of SANs. A comparison of individual current during diastole recorded before and after β1-adrenergic stimulation clearly showed the negative shift of the L-type Ca²⁺ current (I_CaL) takeoff potential, enlargement of the sustained inward current (I_st), and the hyperpolarization-activated nonselective cation current (I_ha) played major roles in increasing the firing frequency. Deactivation of I_Ks during diastole scarcely contributed to the time-dependent decrease in membrane K⁺ conductance, which was the major mechanism for slow diastolic depolarization, as indicated by calculating the instantaneous equilibrium potential (lead potential). This was because the activation of I_Ks during the preceding action potential was negligibly small. However, I_Ks was important in counterbalancing the increase in I_CaL and the Na⁺/Ca²⁺ exchange current (I_NaCa), which otherwise compromised the positive chronotropic effect by elongating the action potential duration. Enhanced Ca²⁺ release from the sarcoplasmic reticulum failed to induce an obvious chronotropic effect in our model.

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The aim of the present study was to investigate whether an expression of vascular cell adhesion molecule–1 (VCAM-1) was upregulated in 3-week simulated microgravity rat cerebral and carotid arteries and whether impaired endothelium–dependent relaxation was concomitant with VCAM-1 expression. Male Sprague-Dawley rats were randomly divided into control (CON) and hindlimb unweighting (HU) groups. After 3 weeks, the expression of the VCAM-1 protein and the vasodilatation of the basilar artery and common carotid artery were determined. Immunohistochemical results revealed positive staining of VCAM-1 on endothelial cells in these arteries from HU compared with CON rats. Western blot analysis confirmed an upregulated expression of VCAM-1 protein in these arteries from HU rats. Acetylcholine induced concentration-dependent vasodilatation in all artery rings, but with significantly smaller amplitude in the basilar artery (P < 0.01) and the common carotid artery (P < 0.05) from HU than those from CON rats. The data suggested that the expression of VCAM-1 protein was upregulated in cerebral and common carotid arteries of simulated microgravity rats, and the upregulation of VCAM-1 may contribute to impaired endothelium–dependent relaxation in simulated microgravity rat vasculature.

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We assessed the contribution of dietary protein to circadian changes in core body temperature (T_b) and metabolic rate in freely moving rats. Daily changes in rat intraperitoneal temperature, locomotor activity (LMA), whole-body oxygen consumption (VO₂), and carbon dioxide production (VCO₂) were measured before and during 4 days of consuming a 20% protein diet (20% P), a protein-free diet (0% P), or a pair-fed 20% P diet (20% P-R). Changes in T_b did not significantly differ between the 20% P and 20% P-R groups throughout the study. The T_b in the 0% P group remained elevated during the dark (D) phase throughout the study, but VO₂, VCO₂, and LMA increased late in the study when compared with the 20% P-R group almost in accordance with elevated T_b. By contrast, during the light (L) phase in the 0% P group, T_b became elevated early in the study and thereafter declined with a tendency to accompany significantly lower VO₂ and VCO₂ when compared with the 20% P group, but not the 20% P-R group. The respiratory quotient (RQ) in the 0% P group declined throughout the D phase and during the early L phase. By contrast, RQ in the 20% P-R group consistently decreased from the late D phase to the end of the L phase. Our findings suggest that dietary protein contributes to the maintenance of daily oscillations in T_b with modulating metabolic rates during the D phase. However, the underlying mechanisms of T_b control during the L phase remain obscure.

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Plasminogen activator (PA) is the enzyme converting plasminogen to its active form, plasmin, involved in various physiological and pathological phenomena. The conversion is catalyzed by two types of PA, urokinase-type PA (uPA) and tissue-type PA (tPA). When human dental pulp cells were stimulated by the inflammatory cytokine tumor necrosis factor-α (TNF-α), PA activity in the conditioned medium was increased, indicating that TNF-α provoked PA secretion. The TNF-α–induced PA release was significantly enhanced in the presence of phorbol-12-myristate-13-acetate (PMA), a protein kinase C (PKC) activator. The PKC inhibitor Ro31-8220 abolished the effect of PMA on the PA release. The activity of PA secreted from the cells stimulated by TNF-α and PMA was reduced by immunoprecipitation using anti-uPA antibody. PMA failed to enhance the TNF-α–induced expression of uPA mRNA. These results suggest that protein kinase C synergistically enhances the secretion of uPA in TNF-α–stimulated human dental pulp cells.

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