We isolated a mouse Sall1, a mammalian homologue of the Drosophila region-specific homeotic gene spalt (sal), and found that mice deficient in Sall1 die in the perinatal period from kidney agenesis. Sall1 is expressed in the metanephric mesenchyme surrounding the ureteric bud, and the homozygous deletion of Sall1 results in an incomplete ureteric bud outgrowth. Therefore Sall1 is essential for ureteric bud invasion, the initial key step for metanephros development. We also set up an in vitro culture system, using NIH3T3 cells stably expressing Wnt4 as a feeder layer, to identify kidney progenitors in the metanephric mesenchyme. In this culture condition, a single renal progenitor in the mesenchyme forms colonies consisting of several types of epithelial cells that exist in glomeruli and renal tubules. We found that only cells strongly expressing Sall1 (Sall1-GFP^high cells) form colonies and that they reconstitute a three-dimensional kidney structure in an organ culture setting. Thus our colony-forming assay, which identifies multipotent progenitors in the embryonic mouse kidney, can be used for examining mechanisms of renal progenitor differentiation.

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Somatic afferent regulation of heart rate by noxious knee joint stimulation has been proven in anesthetized cats to be a reflex response whose reflex center is in the brain and whose efferent arc is a cardiac sympathetic nerve. In the present study we examined whether articular stimulation could influence heart rate by this efferent sympathetic pathway in spinalized rats. In central nervous system (CNS)-intact rats, noxious articular movement of either the knee or elbow joint resulted in an increase in cardiac sympathetic nerve activity and heart rate. However, although in acutely spinalized rats a noxious movement of the elbow joint resulted in a significant increase in cardiac sympathetic nerve activity and heart rate, a noxious movement of the knee joint had no such effect and resulted in only a marginal increase in heart rate. Because this marginal increase was abolished by adrenalectomy suggests that it was due to the release of adrenal catecholamines. In conclusion, the spinal cord appears to be capable of mediating, by way of cardiac sympathetic nerves, the propriospinally induced reflex increase in heart rate that follows noxious stimulation of the elbow joint, but not the knee joint.

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The transverse stiffness of single myofibrils of skeletal and cardiac muscles was examined by atomic force microscopy. The microscopic images of both skeletal and cardiac myofibrils in a rigor state showed periodical striation patterns separated by Z-bands, which is characteristic of striated muscle fibers. However, sarcomere patterns were hardly distinguishable in the stiffness distributions of the relaxed myofibrils of skeletal and cardiac muscles. Myofibrils in a rigor state were significantly stiff compared with those in a relaxed state, and in each state, cardiac myofibrils were significantly stiffer compared with skeletal myofibrils. By proteolytic digestions of sarcomere components of myofibrils, it was suggested that cardiac myofibrils are laterally stiffer than skeletal myofibrils because Z-bands, connectin (titin) filament networks, and other components of sarcomere structures for the former myofibrils are stronger than those for the latter.

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We investigated the effects of visceral stimulation by colorectal distension (CRD) on mean arterial blood pressure (MAP) and renal sympathetic nerve activity (RSNA), the latter being an index of vasoconstrictor activity, in anesthetized central nervous system (CNS)-intact and C2 spinalized rats. The CRD stimulation was induced by the distention of a balloon inserted into the colorectum. In CNS-intact rats, there were significant reductions in MAP and RSNA in response to intraballoon pressures of 60 and 80 mmHg, but not to 20 and 40 mmHg. However, spinalized rats demonstrated significant increases in MAP in response to intraballoon pressures of 60 and 80 mmHg and increases in RSNA in response to intraballoon pressures of 40, 60, and 80 mmHg. These results suggest that noxious visceral stimulation at lower spinal levels reduces MAP by inhibiting sympathetic output in CNS-intact anesthetized rats. On the other hand, noxious visceral stimulation results in an increase in sympathetic-induced MAP in spinalized anesthetized rats.

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To elucidate the influence of heat stress on cutaneous vascular response in the lower extremities during orthostatic stress, a head-up tilt (HUT) test at angles of 15°, 30°, 45°, and 60° for 4 min each was conducted under normothermic control conditions followed by whole-body heat stress produced by a hot water-perfused suit in healthy volunteers. Skin blood flows (SkBF) in the forearm, thigh, and calf were monitored using laser-Doppler flowmetry throughout the experiment. Furthermore, to elucidate the effects of increased core and local skin temperatures on the local vascular response in calf skin under increasing orthostatic stress, the thigh was occluded at 20, 30, 50, 70, and 80 mmHg with a cuff in both the normothermic condition and the whole-body or local heating condition. Significant decreases in forearm SkBF during HUT were observed at an angle of 60° during normothermia and at 30° or more during heating. SkBF in the thigh and calf was decreased significantly by HUT at 15° and above during normothermia, and there was no significant reduction of SkBF in these sites during HUT at the lower angles (15°–45°) during whole-body heating. Significant decreases of calf SkBF were observed at cuff pressures of 20 mmHg and above during normothermia and of 30 mmHg and above during whole-body and local heating, respectively. These results suggest that SkBF in the lower extremities shows a marked reduction compared with the upper extremities during low orthostatic stress in normothermia, and the enhanced skin vasoconstrictor response in the lower extremities is diminished by both whole-body and local heat stress.

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The abundance of voltage-gated L-type Ca²⁺ channels is altered by β-adrenergic receptor (β-AR) stimulation and by an elevation of the intracellular Ca²⁺ concentration in cardiac myocytes. In whole animal, chronic β-AR stimulation or pacing heart results in various changes in the abundance of the channel, but it reduces the β-AR responsiveness of the L-type channel. Because β-AR stimulation facilitates the L-type calcium channels, it is difficult in the whole animal to study the effects of β-AR and Ca²⁺ influx on the upregulation of the L-type channel independently of each other, which makes the cultur of nonbeating adult myocytes an attractive model. We found that culturing quiescent adult rabbit ventricular myocytes with isoproterenol (ISO, 2 μM) for 72 h or more caused a significant increase in the expression of mRNA coding for the L-type channel α_1C subunit by approximately twofold as compared to time-matched controls, and it was followed by a 1.8-fold increase in the Ca²⁺ current density at 96 h. Somewhat surprisingly, an acute application of 1 μM ISO increased the current amplitude even in ISO-treated cells. The increase in the current density, induced by sustained β-AR stimulation, was blocked by a β-AR antagonist, propranolol (10 μM), but not by a Ca²⁺ antagonist, nitrendipine (10 μM). In addition, the effects were reproduced by forskolin (10 μM), but not by a Ca²⁺ agonist, Bay-K 8644 (2 μM). Taken together, these results suggest that sustained β-AR stimulation upregulates L-type channel expression, but does not alter the β-AR responsiveness of the channel in quiescent myocytes.

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We investigated the association between sympathetic nerve activity and delayed rectifier potassium current (I_K) in hypertrophic rat hearts. Left ventricular hypertrophy was induced by a 50% constriction of suprarenal abdominal aorta for 6 weeks. The effects of isoproterenol on action potential duration (APD), I_K, and L-type calcium current (I_Ca) were investigated using the whole-cell patch clamp technique. In hypertrophic rats, I_K was decreased by 28.2%, resulting in significant APD₉₀ (90% repolarization) prolongation (sham: 55 ± 3.9, hypertrophy: 98 ± 11 ms, P = 0.01). Isoproterenol (100 nM)-stimulated I_K was increased by 54.9% ± 0.10% in sham-operated rats, but not in hypertrophic rats. On the other hand, isoproterenol increased I_Ca in both sham-operated (77.7% ± 7.6%) and hypertrophic rats (69.6% ± 9.7%). Consequently, isoproterenol prolonged further APD in hypertrophic rats (98 ± 11 vs. 145 ± 8.6 ms, P < 0.01), but not in sham-operated rats (55 ± 3.9 vs. 61 ± 5.6 ms, n.s.). Forskolin (1 μM, an adenylyl cyclase stimulator) did not enhance I_K in hypertrophic rats, but IBMX (100 μM, a nonselective phosphodiesterase inhibitor) enhanced the current (30.2 ± 0.05%), as much as in sham-operated rats. We concluded that in hypertrophic hearts, I_K was not increased by isoproterenol because of the enhanced activity of phosphodiesterase, which leads to excessive APD prolongation.

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The aim of this study was to examine the effects of the sitting posture on the lower limb venous flow and to explore the beneficial effects of neuromuscular electrical stimulation (NMES) and an ottoman-type seat on the venous flow. Healthy adult volunteers without a history of lower limb surgery or thromboembolism were recruited, and the flow velocity, cross-sectional area, and flow volume of the popliteal vein were measured using Doppler ultrasound. A posture change from the prone position to the sitting position on the ottoman-type seat decreased the flow velocity and increased the cross-sectional area of the popliteal vein, and the flow volume was not altered over 120 min. The flow velocity was further decreased, and the cross-sectional area was further increased by subjects sitting on a regular driving seat when compared with the values obtained with an ottoman-type seat. The popliteal flow velocity in the NMES leg was significantly higher than in the non-NMES leg throughout the 120-min testing in the sitting position, but no difference in the cross-sectional area was found between the NMES and the non-NMES legs. Thus lower limb venous stasis elicited by the sitting posture was improved by the ottoman-type seat and NMES.

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Colorectal distensions of 60 and 80 mmHg significantly reduced heart rate (HR) and cardiac sympathetic nerve activity in anesthetized rats. This bradycardiac response was not influenced by the intravenous administration of atropine, but was abolished by propranolol, suggesting that it was elicited by sympathetic but not vagal efferent nerves.

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