Repetitive intermittent cold exposure (5°C, 6h/day, 4 weeks) (ICE) resulted in the same cold adaptability as assessed by an enhanced cold tolerance (less drop of colonic temperature at -5°C) and nonshivering thermogenesis (NST) (greater noradrenaline-induced heat production) as that elicited by continuous cold exposure (5°C, 4weeks) (CA) in rats. Although shorter intermittent (5°C, 2h/day, 4weeks) (ICE-2hr) as well as shorter continuous (5°C, 1 week) (CA-1wk) cold exposure effected an improved cold adaptability, the magnitude of cold tolerance and NST was smaller as compared with that in CA and ICE. The cold deacclimation process as reflected on the decreased NST did not differ between CA and ICE. Food intake was less in ICE than CA, while increase in body weight during the acclimation period was greater in the former. Increase in adrenal weight was greater in CA than ICE, but plasma corticosterone level did not differ among warm controls (WC), CA, and ICE in resting state (after 18-20h at warm control temperature of 25°C). Weights of interscapular and dorsocervical brown adipose tissue (BAT) increased to the same degree in CA and ICE. Plasma glucagon level in resting state did not differ among groups, while BAT glucagon levels significantly increased in CA and ICE, but they were higher in dorsocervical site than interscapular site in all acclimated states. Acute cold exposure (-5°C, 15min) caused increases in plasma corticosterone, glucagon levels, and in BAT glucagon levels in all acclimated groups. The extent of increase was significantly less for plasma glucagon in CA, while plasma corticosterone increased similarly in all groups. These results indicate that repetitive short-term cold exposure could elicit the same cold adaptability as that induced by continuous exposure, but requiring only one-fourth of the time of continuous cold exposure. Moreover, it is suggested that glucagon is involved in both CA and ICE, but the same extent of cold adaptability can be obtained in the less energy-requiring and less stressful state in ICE.

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Wood mice (Apodemus argenteus) were trapped live at three different altitudes (below 1, 000, 1, 900, and 2, 400m) during a 1-year period (Feb. 1984-Jan. 1985). After remaining at the trapped locations for 10-14 days, they were transferred into a climatic chamber at an altitude of 610m. Oxygen consumption (V_O2) and colonic temperature (T_co) were measured at chamber temperatures (T_a) of five steps (30, 20, 10, 0, and -10°C) in freely moving conditions. In response to T_a of 0°C for the mice trapped in winter when their mean local habitat temperature (T_e) were lower than 0°C, there was a significant inverse correlation between V_O2 and T_e (r=-0.70, p<0.001) whereas no significant correlation (r=0.23) was observed in the mice trapped in other seasons when T_e was higher than 0°C. The correlation between T_co and T_e was significant (r=-0.66, p<0.001) over the entire range of T_e. The pelt weight of the mice trapped at T_e higher than 0°C had a significant inverse correlation with T_e (r=-0.65, p<0.001), but not in the mice trapped at T_e lower than 0°C. After measurement of V_O2 and T_co at T_a of 0°C, the mice who had lived in colder habitats (below 0°C) showed 0% mortality, whereas the mortality of the populations which had lived in warmer habitats was 13%. These results suggest that, in wood mice, adaptation to severe cold is established by an enhanced thermogenesis and by an increased insulation of the pelt in moderate cold.

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Effects of Ca²⁺ -induced Ca²⁺ release blockers, ruthenium red (RR) and Mg²⁺, on Ag⁺-induced Ca²⁺ release were studied using skinned muscle fibers or fragmented heavy SR (HSR) prepared from frog muscle, and compared with those on caffeine-induced one. Exposure of the skinned fibers to 5μM Ag⁺ produced a rapid and large contraction in the presence of 0.043mM free Mg²⁺. When Mg²⁺ concentration was increased to 0.86mM, Ag⁺ led to a large transient contraction, combined with a small tonic one. The transient component was completely blocked by high Mg²⁺ (3.64mM), but the tonic one was not. Ca²⁺-ATPase activity was not stimulated by increase of Mg²⁺ from 0.86 to 3.64mM. Ag⁺ and caffeine induced a rapid Ca²⁺ efflux from HSR in a dose-dependent manner. RR over a range from 1 to 10μM dose-dependently inhibited the Ca²⁺ efflux induced by 10μM Ag⁺. Despite increase of RR to 30μM, however, further inhibition of the Ca²⁺ efflux was not produced any more (77.8±12.2% inhibition). A 10mM caffeine-induced efflux of Ca²⁺ was blocked slightly by only 0.5μM RR and almost completely by 3μM. A slight inhibition (about 28%) of the Ca²⁺-ATPase activity was observed in the presence of 10μM Ag⁺ in 0.5mg SR protein/ml of medium. RR and caffeine did not affect the enzyme activity. These results indicate that frog SR could induce a rapid release of Ca²⁺ upon Ag⁺ and caffeine, suggesting that Ag⁺ may have two different binding sites to release Ca²⁺; one is on Ca²⁺-induced Ca²⁺ release channel and the other on RR-insensitive site.

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Six males performed cycle ergometer exercise on two occasions in random order. Each exercise was preceded by a 2-h period in which matched capsules were administered orally, containing either starch (C) or NaHCO₃ (E) in a dose of a 0.2g•kg^-1 body wt; pre-exercise blood pH and [HCO₃^-] were 7.34±0.01 and 23.7±0.5mM (mean±S.E.) for the C study, and 7.41±0.01 and 28.6±1.3mM for the E study (p<0.001 and p<0.01, respectively). Exercise was continuous and maintained for 10min at 40% of maximal oxygen uptake (40% V_O2max), followed by 15min at 12W above the respiratory compensation threshold ([+RCT]) which was determined by the increase of the ventilatory equivalent for carbon dioxide (VE•V_CO2^-1), and for as long as possible at 95% V_O2max. Endurance time at 95% V_O2max was significantly longer in E than in C (2.98±0.64min vs. 2.00±0.44min, p<0.05). The rate of increase in arterialized venous lactate (LA) was higher in E than in C from rest to exercise at [+RCT], while there was no significant difference in the hydrogen ions ([H⁺]). Consequently, [H⁺]•LA^-1 (nM•mM^-1) was significantly lower in E than in C. The change of VE•V_CO2^-1 was shifted downward in E compared to C during exercise with the lowest value being observed at the same exercise stage. These results suggest that the respiratory responses to exercise are not affected by the higher level of [HCO₃^-] induced by NaHCO₃ ingestion, and appear to reflect the net change of plasma [HCO₃^-] or [H⁺]. Also, induced metabolic acidosis has little effect on [H⁺] appearance in blood.

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In order to examine the role of respiratory oscillation of Pa_CO2 (CO₂ oscillation) in the control of respiration, we performed veno-venous bypass using a membrane lung in 10 anesthetized paralyzed dogs, where the dog was put on fixed mechanical ventilation so that we could keep average Pa_CO2 and Pa_O2 constant by adjusting FI_CO2 and FI_O2 during CO₂ loading/unloading. By venous CO₂ loading/unloading we could widely change the CO₂ output from the lung (11-440% of the control) resulting in large changes in the arterial CO₂ oscillations (50-280% of the control for the maximum rate of rise of Pa_CO2 and 40-350% of the control for the maximum rate of fall of Pa_CO2), which was measured by a rapidly responding intra-arterial pH electrode. Despite such wide variations in CO₂ oscillations we did not find any consistent change in the respiratory center output (minute phrenic activity). This held true after compensating the changes in the minute phrenic activity for the CO₂ sensitivity of each individual dog. Thus, the present results may suggest that the CO₂ oscillation plays little role in the control of respiration in mild increase in V_CO2.

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Catecholamine (CA) secretion induced by Ca re-introduction or ouabain in the presence of Ca is markedly potentiated by Bay-K-8644 in the perfused cat adrenal. The mechanism of potentiation by this Ca agonist was investigated using perfused cat adrenal and isolated bovine chromaffin cells. The stimulatory effect of Bay-K-8644 on the response to Ca was very slight when cat adrenal was perfused with a Ca-deficient medium, in which 1mM Mg was added or the concentration of Na was lowered. The inhibitory effect of Mg was reversed by inhibition of the Na pump with K deprivation, ouabain, or KCN. The secretion induced by ouabain during maintained depolarization at a lowered concentration (0.25mM) of Ca, which is supposed to be due to Ca influx in exchange for Na efflux, was larger in the Bay-K-8644 treated adrenal than that in the untreated adrenal. The increase in secretion by the delayed addition of Bay-K-8644 during perfusion with a high K medium containing ouabain was larger when the concentration of Na in a high K medium was higher. When isolated chromaffin cells were stimulated with a Na-free (Tris) medium containing 0.5mM Ca, CA secretion from and ⁴⁵Ca uptake into the cells preincubated with a divalent cation-free medium were potentiated by Bay-K-8644. The stimulatory effect of Bay-K-8644 was not seen when a Ca-free treatment medium contained Mg or lacked Na, but the inhibitory effect of Mg was reversed by the addition of ouabain or KCN to the pretreatment medium. When isolated cells preloaded with ⁴⁵Ca were superfused with a Ca-free medium, Ca re-introduction increased the rate of Ca efflux only under conditions in which significant increases in CA secretion and ⁴⁵Ca uptake were previously observed under the static incubation system. Bay-K-8644 further increased this Ca efflux rate under these conditions. These results support the view that Ca influx linked with Na efflux is through a pathway with properties similar to those of voltage-dependent Ca channels, and suggest that this Ca pathway is activated by Bay-K-8644, which is an activator of voltage-dependent Ca channels.

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The effect of electromagnetic induction (EMI) on impulse conduction and muscle contraction was studied in isolated sciatic nervegastrocnemius muscle preparation of the frog. Electrical stimulation (ES) of the sciatic nerve, at 0.5Hz with 0.6V (supramaximal) and 1-ms pulse duration, produced twitch contractions (3.5±0.4g tension, mean±S.E., n=8 frogs), which were reduced or blocked by EMI, applied to the nerve via an induction coil, from a d.c. source of 1.5-4V, at a frequency of 100 min^-1, for 2- to 4-min duration. Recovery of the blocked twitches was obtained within 4-5min, after the cessation of the EMI and washing out the preparation in Ringer solution. The inhibition of the twitch tension by EMI was compared to that produced by an effective concentration of a local anaesthetic, lignocaine (1μM), which is known to block conduction, by blocking ionic fluxes across the nerve membrane. It is possible that EMI also interferes with the ionic fluxes, and in prolonged duration, may produce changes in the myelin sheath (or the Schwann cells) of the nerve membrane. A comparison of ES with EMI was made, and it was concluded that EMI inhibited electrically induced neuromuscular transmission at the frog neuromuscular junction.

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Brown adipose tissue (BAT) glucagon level was higher in cold-acclimated rats (CA) than in warm controls (WC). Noradrenaline (NA) injection increased BAT glucagon levels in both WC and CA with increases in plasma glucagon levels. The magnitude of increase was significantly greater in CA for plasma glucagon, while it did not differ for BAT between groups. However, BAT glucagon was kept at a higher level in CA after NA injection than in WC.

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A conjugate preparation of antibody (Fab) and tetramethylrhodamine (TMR) generally adsorbs free TMR which is very difficult to remove because of its strong hydrophobic binding. On the basis of criteria such as sodium dodecyl sulfate (SDS) gel electrophoresis and staining of the plasma membrane of live cells, we found that simple extraction with n-butyl alcohol or iso-amyl alcohol could remove the contaminating free dye. The procedure is especially useful when one needs to prepare conjugates with low nonspecific binding for the study of lateral diffusion of cell membrane-associated antigens.

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The lactate (LA) kinetics of the whole body in exercise was described using the two-compartment model in consideration of the underlying physiological mechanism, and LA kinetics during the ramp mode exercise was analyzed. The estimated pattern of the glycolytic energy supply showed the progressive increase concurrently with the onset of ramp mode exercise and this pattern was just like a ramp phenomenon. Based on this result, it is proposed that blood LA kinetics during ramp exercise should be described mathematically as a continuous model, called "2nd-order model."

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