In the circular muscle of the guinea-pig gastric antrum, a decrease in the external Na⁺ to less than 20 mM produced depolarization of the membrane with transient prolongation of the slow wave. This was followed by a high rhythmic activity. The activity was inhibited by reapplication of Na⁺ before recovery. The depolarization in Na⁺-deficient solution was prevented and rhythmic activity continued at about 5/min for at least 6 min by simultaneous removal of K⁺, Ca²⁺, or Cl⁻. After exposure to a Na⁺- and Cl⁻-deficient solution for a few minutes, reapplication of the Na⁺ in Cl⁻-deficient solution inhibited generation of the slow wave until Cl⁻ reapplication. Similar results were obtained when Na⁺ and Cl⁻ were reapplied in the absence of K⁺ after exposure to a Na⁺-, K⁺-free , and Cl⁻-deficient solution, although the inhibition was weaker than Na⁺ reapplication in a Cl⁻-deficient solution. In the presence of furosemide or bumetanide, a strong inhibition of activity was produced by the reapplication of Na⁺ and Cl⁻ after exposure to an Na⁺- and Cl⁻-deficient solution. A hypothesis is presented that intracellular Ca²⁺ concentration ([Ca²⁺]_i) is the most important factor determining the generation and frequency of the slow wave and that [Ca²⁺]_i is regulated by the Na⁺ concentration gradient across the plasma membrane. The recovery of the Na⁺ concentration gradient by Na⁺ reapplication after removal of Na⁺ and Cl⁻ is mainly controlled by a Na⁺-K⁺-Cl⁻ co-transport.

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We have found that a logistic function fits the left ventricular isovolumic relaxation pressure curve in the canine excised, cross-circulated heart more precisely than a monoexponential function. On this basis, we have proposed a logistic time constant (τ_L) as a better index of ventricular isovolumic lusitropism than the conventional monoexponential time constant (τ_E). We hypothesize in the present study that this τ_L would also be a better index of myocardial isometric lusitropism than the conventional τ_E. We tested this hypothesis by analyzing the isometric relaxation force curve of 114 twitches of eight ferret isolated right ventricular papillary muscles. The muscle length was changed between 82 and 100% L_max and extracellular Ca²⁺ concentrations ([Ca²⁺]_o) between 0.2 and 8 mmol/l. We found that the logistic function always fitted the isometric relaxation force curve much more precisely than the monoexponential function at any muscle length and [Ca²⁺]_o level. We also found that τ_L was independent of the choice of the end of isometric relaxation but τ_E was considerably dependent on it as in ventricular relaxation. These results validated our present hypothesis. We conclude that τ_L is a more reliable, though still empirical, index of lusitropism than conventional τ_E in the myocardium as in the ventricle.

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In animals, female sex steroid hormones (SS, estrogens-progesterone) influence the energy substrate that is metabolized. Human research on this issue is controversial. This study examined whether changes in circulating SS hormone levels affected the carbohydrate-lipid metabolism during submaximal prolonged (60 min) exercise. Young, physically active females were studied. Four were classified as anovulatory-oligomenorrheic and four were classified as ovulatory-eumenorrheic. Subject responses were pooled to form one group (n = 8) and then their responses under low (L) and high (H) pharmaceutically manipulated SS hormone conditions were examined. During exercise, the mean oxygen consumption levels were 1.70 ± 0.10 l·min⁻¹ for L-SS and 1.75 ± 0.11 l·min⁻¹ for H-SS (p = 0.07), respectively. The respiratory exchange ratio (RER) responses were significantly different during exercise between the conditions: 0.93 ± 0.04 for L-SS and 0.90 ± 0.04 for H-SS (p < 0.05), respectively. RER responses were utilized to calculate substrate oxidation. Significantly less carbohydrate oxidation was found in the H-SS condition as compared to the L-SS condition (p < 0.05). Lipid oxidation was also significantly different, but for this measure, the levels of oxidation were greater in the H-SS than in the L-SS condition (p < 0.05). Finally, total energy expenditure for the 60 min of exercise was not significantly different between the hormonal conditions. Results suggest that sex steroid hormones have an impact upon substrate oxidation in women during exercise. Specifically, high circulating concentrations of the SS hormones result in an enhanced reliance upon the oxidation of lipid as an energy substrate and consequently induce a reduction in carbohydrate oxidation. The mechanism inducing this "metabolism shift" appears due to sex steroid hormones directly and indirectly increasing lipid mobilization and lipolysis.

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The effect of acupuncture-like stimulation of various areas (cheek, forepaw, upper arm, chest, back, lower leg, hindpaw, perineum) on cortical cerebral blood flow (CBF) was examined in anesthetized rats. An acupuncture needle (diameter, 340 μm) was inserted into the skin and underlying muscles at a depth of about 5 mm and twisted to the right and left once a second for 1 min. CBF of the cortex was measured using a laser Doppler flowmeter. Stimulation of the cheek, forepaw, upper arm and hindpaw produced significant increases in CBF, but stimulation of the chest, back, lower leg and perineum did not produce significant responses. Stimulation of the cheek, forepaw, and hindpaw produced an increase in mean arterial pressure (MAP), while stimulation of the back produced a decrease in MAP. Stimulation of the upper arm, chest, lower leg and perineum did not produce a significant MAP response. After spinal transection at the 1st to 2nd thoracic level, the blood pressure response to stimulation of the cheek and forepaw was suppressed, whereas an increase in CBF still took place. The increase in CBF induced by forepaw stimulation was abolished by severance of the somatic nerves at the brachial plexus. Forepaw stimulation enhanced the activity of the radial, ulnar and median nerves. Furthermore, in the present study, passing of an electric current through acupuncture needles showed that excitation of group III (Aδ) and group IV (C) afferent fibers in the somatic nerve was capable of producing an increase in CBF, whereas excitation of group I (Aα) and group II (Aβ) fibers was ineffective. The increase in CBF induced by forepaw stimulation was almost abolished by intravenous administration of muscarinic and nicotinic cholinergic blocking agents (atropine 5 mg/kg and mecamylamine 20 mg/kg), and by bilateral lesions in the nucleus basalis of Meynert. Acupuncture-like stimulation of a forepaw increased acetylcholine release in the cerebral cortex. We concluded that the increase in CBF, independent of systemic blood pressure, elicited by acupuncture stimulation is a reflex response in which the afferent nerve pathway is composed of somatic group III and IV afferent nerves, and efferent nerve pathway includes intrinsic cholinergic vasodilators originating in the nucleus basalis of Meynert. acupuncture, neural regulation of cerebral blood flow, intracranial cholinergic vasodilative system, nucleus basalis of Meynert, extracellular acetylcholine.

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Electroneurograms (ENGs) from superficial regions of the sciatic nerve of a Beagle dog were recorded selectively with a chronically implanted 33-electrode spiral cuff (cuff). By delivering stimulating pulses to groups of three electrodes (GTEs) within the cuff we could define the relative positions of the particular superficial regions that selectively innervated the tibialis anterior (TA) and gastrocnemius muscles (GM). GTEs with and without contractions of the TA and GM muscles were selected and connected to a 4-channel ENG system designed to amplify ENGs by 100,000 times and to pass frequencies between 500 Hz and 10 kHz. In our study, 12 experiments were conducted on three Beagle dogs with a cuff implanted for up to 2 years. We present the results obtained in four experiments conducted on one animal. With the implanted leg mounted in a special electronic brace we applied extending forces to the ankle, rotating it by up to 37° according to the neutral position, eliciting torque to stretch the TA muscle. Only the ENG from a GTE eliciting maximum contraction of the TA muscle showed activities corresponding to the trajectory of the mechanical load of the muscle. Next, we dissected the calcanean tendon (CT) of the implanted leg and applied repetitive pull forces to the CT. Only the ENG from the GTE eliciting maximum contraction of the GM muscle was activated in correspondence to the trajectory of the mechanical load applied on the CT. The results suggest that the cuff, implanted chronically on the sciatic nerve, is useful to record ENGs of the afferent fibers from TA and GM muscles selectively and that the technique could be extended for human use in the field of rehabilitation for paralysis.

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It is unclear whether preceding repetitive brief ischemia causes any improvement in the energy efficiency of intracellular calcium cycling or crossbridge cycling that may lead to cardioprotection after subsequent sustained ischemia/reperfusion, a phenomenon called ischemic preconditioning. To address this issue, left ventricular (LV) contractility (E_max) and the relation between myocardial oxygen consumption (V^·O₂) and pressure-volume area (PVA, a measure of LV total mechanical energy) were assessed before (Control) and 20 min (Rep-20) and 60 min (Rep-60) after repetitive brief ischemia in 11 isolated, blood-perfused dog hearts. At Rep-20, E_max and PVA-independent V^·O₂ (nonmechanical energy expenditure) decreased by 23.0 ± 19.5 and 13.9 ± 18.0%, respectively (both p < 0.05). However, at Rep-60, both E_max and PVA-independent V^·O₂ recovered to their respective control levels. The oxygen cost of contractility (the slope of the PVA-independent V^·O₂-E_max relation during CaCl₂ loading) remained constant (Control 0.0019 ± 0.0009 vs. Rep-60 0.0018 ± 0.0013 ml O₂·ml·mmHg⁻¹·beat⁻¹·100 g⁻², ns), suggesting unchanged efficiency in Ca²⁺ cycling. Also, the contractile efficiency (the reciprocal of the slope of the V^·O₂-PVA relation, reflecting the efficiency of crossbridge cycling) was the same between the Control and Rep-60 (53.7 ± 16.7 vs. 55.4 ± 14.4%, ns). Basal metabolism V^·O₂ during KCl arrest was also similar to that in the normal heart. Nonmechanical energy expenditure was reduced in proportion to the decrease in LV contractility after repetitive brief ischemia, while both the contractile efficiency and oxygen cost of contractility remained constant. These results indicate that the heart, after repetitive brief ischemia but before sustained ischemia, has normal efficiencies of crossbridge cycling and Ca²⁺ cycling despite the transiently reduced contractility.

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To test the hypothesis that a complex of cyclin-dependent kinase 5 (Cdk5) and p35^nck5a plays an important role in sprouting in the kindling rat hippocampus, we studied the changes in kinase activity, expression level and subcellular localization during kindling progression. The kinase activity in kindling rats was significantly higher than that in normal rats. The changes in kinase activity coincided with those of the p35^nck5a expression in kindling rats. In contrast, the expression of Cdk5 was constant at all stages of kindling. Subcellular localization of Cdk5, however, changed markedly in the hippocampal neurons during kindling progression. Cdk5 translocated from axon to soma when the kinase activity was high. The phosphorylation level of tau protein was in good agreement with the Cdk5 kinase activity. In contrast, MAP kinase activity was not correlated with tau phosphorylation during kindling progression. These findings suggest that Cdk5/p35^nck5a plays an important role in synaptic reorganization, and the translocation of Cdk5 to soma from axons is a crucial regulatory mechanism of kinase activity.

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A novel experimental method was developed to study the contractility of single myofibrils of skeletal muscle. Single myofibrils (ca. 1 μm in diameter) prepared from glycerinated rabbit psoas muscle were suspended between rigid and flexible microneedles by the entwining method. The length changes of the preparations applied via the rigid microneedle by an actuator and the force produced were measured by photo-electrically detecting the nanometer deflections of the flexible microneedle. Single myofibril preparations maintained uniform sarcomere striations during contraction-relaxation cycles. The isometric force produced, the velocity of unloaded shortening, and the force-velocity relationship of single myofibrils were investigated at various MgATP concentrations. The contractility of single myofibrils thus obtained in the absence of ATP regenerative systems was essentially the same as that of skinned muscle fibers under comparable conditions in the presence of ATP regenerative systems. Thus, it was found that (1) the present experimental method is useful for studying the contractility of single myofibrils, and (2) in single myofibril preparations, the MgATP concentration at actomyosin sites is well equilibrated with that in bathing solutions.

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Whether 2,3-butanedione monoxime (BDM, ≤5 mmol/l) suppresses primarily crossbridge cycling or total Ca²⁺ handling in the blood-perfused whole heart remains controversial. Although BDM seems to suppress primarily total Ca²⁺ handling in canine hearts, more evidence is lacking. We therefore analyzed the cardiac mechanoenergetics, namely, E_max (contractility), PVA (total mechanical energy), and O₂ consumption of canine BDM-treated hearts by our recently developed integrative method to assess myocardial total Ca²⁺ handling. This method additionally required the internal Ca²⁺ recirculation fraction. We obtained this from the beat constant of the exponential decay component of the postextrasystolic potentiation. Our analysis indicated significant decreases in both internal Ca²⁺ recirculation fraction and total Ca²⁺ handling in the BDM-treated heart, but virtually no change in the reactivity of E_max to total Ca²⁺ handling. This result corroborates the view that BDM suppresses primarily total Ca²⁺ handling rather than crossbridge cycling in the canine blood-perfused heart.

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The fast Fourier transform (FFT) is a good method to estimate power spectral density (PSD), but the frequency resolution is limited to the sampling window, and thus the precise characteristics of PSD for short signals are not clear. To relax the limitation, a multiple band-pass filter was introduced to estimate the precise course of PSDs for flash visual evoked potentials (VEPs). Signals were recorded during −200 and 600 ms using balanced noncephalic electrodes, and sampled at 1,000 Hz in 12 bits. With 1 Hz and 10 ms resolutions, PSDs were estimated between 10 and 100 Hz. Background powers at the alpha- and beta-bands were high over the posterior scalp, and powers around 200 ms were evoked at the same bands over the same region, corresponding to P110 and N165 of VEPs. Normalized PSDs showed evoked powers around 200 ms and suppressed powers following the evoked powers over the posterior scalp. The evoked powers above the 20 Hz band were not statistically significant, however, the gamma band was significantly evoked intra-individually; details in the gamma bands were varied among the subjects. Details of PSDs were complicated even for a simple task such as watching flashes; both synchronization and desynchronization occurred with different distributions and different time courses.

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