For skeletal muscle, the physiological meaning of Hill's hyperbolic force-velocity equation and the factors affecting it, such as the active state, method of velocity measurement and mode of stimulation, have been discussed. After the development of the sliding filament theory, Hill's equation was generalized to all partially activated isometric tensions and the meaning of Hill's dynamic constants was interpreted from the kinetic analysis of the cross-bridge cycle. In cardiac muscle, determination of the precise force-velocity relation was almost impossible, but most difficulties were overcome by tetanizing the cardiac muscle. As a result, the force-velocity properties of cardiac muscle were confirmed to be very similar to those of skeletal muscle. The maximum shortening velocity under no load, v₀, was once used as an index of myocardial contractility which is insensitive to muscle length, but it is now believed that at least at shorter lengths, v₀ may vary with muscle length and degree of activation. As new approaches, studies on sarcomere dynamics by the laser diffraction method, observation of calcium transient and pressure-velocity measurement in whole ventricle have been introduced.

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The cat adrenal gland was retrogradely perfused with a medium lacking divalent cation, and the secretion of catecholamines was induced by Ca reintroduction with or without simultaneous removal of external Na. These responses were markedly reduced after prior exposure to a medium containing Mg (1mM) or lacking Na. The inhibition caused by Mg was reversed by ouabain treatment. Reversing the concentration gradient for Na alone by replacing external Na with Tris, choline, or Li did not stimulate catecholamine secretion when Ca²⁺ (0.1mM) was present in the external medium throughout the experiment. However, the treatment with ouabain reversed this inhibitory effect of Ca so that Na removal did induce marked secretion. Essentially similar results concerning secretion were obtained in the cultured bovine chromaffin cells. There was a reasonable correlation between secretion and ⁴⁵Ca uptake in these cells under various experimental manipulations, and alterations of these parameters were well correlated with the level of internal Na. Furthermore, the rate constant of ²²Na efflux was found to increase when Ca was reintroduced with the simultaneous removal of Na during exposure to a medium containing ouabain. These results are consistent with the view that the mechanism of internal Na-dependent Ca influx is activated to induce catecholamine secretion whenever internal Na is raised above a critical level. On the other hand, there were significant increases in the catecholamine secretion and ⁴⁵Ca uptake which were induced by substitution of NaCl with sucrose, even when the operation of the internal Na-dependent Ca influx mechanism was markedly restricted by various experimental manipulations. This suggests that other secretory mechanisms are involved under these conditions. This would account for the largest secretory effect of sucrose substitution under the condition in which internal Na-dependent Ca influx is activated.

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A method for the isolation of single smooth muscle cells from guinea pig taenia caeci is described. The single cells were prepared by digestion with 0.3% collagenase and 0.6% trypsin inhibitor in Ca²⁺-free solution. This procedure produced a high yield of intact cells. Most cells obtained by this procedure were relaxed and showed large contractile responses to excitatory stimulus. Maximal responses of the single cells to acetylcholine (ACh), histamine, and high K⁺ were attained within 20sec, and the per cent decrease in cell length was 30-40%. Times for maximal responses of the single cells were shorter than those of the muscle strips. Single cells exhibited a dose-dependent graded response to calcium under depolarized conditions, ACh, histamine, and high K⁺, and a voltage- and duration-dependent response to electrical stimulation. The ED₅₀s of ACh in the single cells and in the muscle strips were about 2×10^-8 and 1.5×10^-7M, respectively. The muscle strips had a lower sensitivity than the single cells to ACh. The generally smooth surface of the relaxed cell contrasted with the numerous evaginations present on the fully contracted cell. I believe that single smooth muscle cells isolated from guinea pig using my technique are, at present, better for physiological and pharmacological studies than are cells isolated using other techniques.

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Extracellular responses were recorded from neurons in the thalamic mediodorsal nucleus (MD) of the lightly anesthetized rabbit. Eighty-seven neurons responded to electrical stimulation of the lateral olfactory tract (LOT shocks). They were located in the medial portion of the MD. In the same portion, negative field potentials with a short latency were evoked by the electrical stimulation of the olfactory projection area in the neocortex (OPA shocks). Fifty-nine MD neurons responded both to LOT and to OPA shocks. Among them, 17 thalamocortical relay neurons (which responded antidromically to OPA shocks) were found to respond transsynaptically to LOT shocks. Of the 87 LOT-responsive MD neurons, 48 responded to the odors applied. Eight odor-sensitive neurons were found to be the thalamocortical relay neurons. Thus, it was proven for the first time that a portion of the olfactory input to the OPA is mediated via relay neurons in the MD. Characteristics of response of MD neurons to odor stimulation were compared with those of OPA neurons. MD neurons did not show a selectivity of response to odors of urine, feces, or dry food pellets, to which OPA neurons responded exclusively. These results were discussed in relation to the functional role of the MD-OPA projection system in the discrimination of specific odors.

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The thermal sensitivity of different parts of the body was investigated by heating large areas of the body surface while the mean skin temperature calculated from HARDY and DUBOIS' formula (1938) was always kept constant. The right arm sweating responses recorded under a local thermal clamp were related to changes in segmental skin temperatures of the different parts of the body. The results show that: 1) the various local peripheral signals are projected into integrating structures in the central nervous system; 2) the thermal sensitivity is greater for the head-and-trunk area in comparison with other parts of the body. For resting nude subjects, the formula of Hardy and DuBois remains a pertinent way for evaluating the role of skin thermal signals in the central drive for sweating. The peripheral contribution to the central sweating drive depends only on the skin temperature change and on the size of the stimulated area.

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Inhibitory junction potentials (i. j. p. s) evoked by field stimulation were recorded from the smooth muscle cells of the guinea-pig duodenum intracellularly. The membrane potential was -54.3mV. The parameters of the i. j. p. were as follows: latency, 71msec; time to peak, 146msec; amplitude, 15.5mV; rate of hyperpolarization, 107mV/sec; and half decay time of the i. j. p., 193msec. Met-enkephalin (10^-7-10^-6M) had no effect on the membrane potential and the i. j. p. The membrane potential was decreased by β-endorphin (1.7×10^-7-6.8×10^-7M). Increase in the latency and the time to peak and decrease in the amplitude and the rate of hyperpolarization of the i. j. p. were observed for β-endorphin. "Spontaneous" excitatory junction potentials (e. j. p. s) were generated by β-endorphin. Naloxone (3.1×10^-6-3.1×10^-4M) hyperpolarized the membrane of the muscle cells. At high concentrations of naloxone (3.1×10^-4 and 3.1×10^-3M), inhibition of the i. j. p. was observed. Levallorphan (2.3×10^-4M) prolonged the latency and the time to peak and reduced the amplitude of the i. j. p. The membrane potential was slightly decreased by levallorphan. "Spontaneous" e. j. p. s were generated by levallorphan in a certain population of the cells. It is concluded that Met-enkephalin does not contribute to the non-adrenergic inhibitory transmission and that β-endorphin acts as a modulator in the control mechanism of the intestinal motility. The effects of naloxone and levallorphan on the i. j. p. are discussed.

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The role of the sympathetic nervous system in 10-min cold (5°C)- or 2-min immobilization-induced thermogenesis in brown adipose tissue (BAT) was studied in warm(25°C)-acclimated rats. Both cold- and immobilization-stresses increased heat production (M), interscapular brown adipose tissue temperature (T_bat), and colonic temperature (T_col). Resulting from both stresses, the increase in T_bat was greater than that in T_col, the differences (ΔT_bat) becoming approximately 0.48 and 0.46°C by the cold exposure and the immobilization, respectively. After sympathectomy, T_bat and ΔT_bat did not change on immobilization but increased significantly on the cold exposure. ΔT_bat was 0.31°C in the sympathectomized rats at the end of the cold exposure period. Immobilization-induced BAT thermogenesis may be mainly controlled by the sympathetic nervous system. On the other hand cold-induced BAT thermogenesis seems to be controlled by certain hormonal factors as well as the sympathetic nervous system.

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Circular muscle strips of rat uterus were obtained in the morning on Days 21 and 22 of pregnancy, and on the first postpartum day. Changes in the effects of noradrenaline and isoprenaline due to pregnant stage and incubation period in vitro were investigated, taking the contractile response and membrane activity as indicators. Plateau potential was dominant in Day 21 and postpartum preparations, and spike potential on Day 22. Noradrenaline (3×10^-7, 10^-6 M) caused excitation in Day 21 and postpartum preparations, whereas it caused inhibition in Day 22 preparations during early exposure to Krebs solution. When contractile potentiation was caused, plateau potential was prolonged, and when contractile depression was caused the plateau potential was suppressed. By incubation in vitro with Krebs solution, a transformation of the effect of noradrenaline from excitation to inhibition was caused in Day 21 preparations, and from strong to weak inhibition in Day 22 preparations. Isoprenaline of 3×10^-10M concentration markedly depressed the contractile response in Day 22 preparations, whereas 10^-8M isoprenaline was not enough to suppress the spontaneous contractions in postpartum preparations.

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In the guinea-pig tracheal smooth muscle, tonic contraction, maintained in normal medium, was abolished by Ca removal or by indomethacin (10^-6M). Removal of Na produced a transient contraction followed by a gradual decrease in tension to a level lower than the control. When Na was readmitted, a rapid relaxation was observed. The degree of the relaxation was enhanced with the exposure time to Na-free solution, and with the concentration of Na readmitted. At 5.9mM K, the contraction produced by Ca readmission with simultaneous Na removal became smaller and slower as the external Na was reduced before Ca readmission, while at 40mM K, the Ca-induced contraction was less dependent on the Na concentration. The rate of relaxation on Ca removal was slower when the Na concentration was reduced both at 5.9 and 40mM K. Verapamil (10^-5M) had a weak suppressing effect in normal solution, but suppressed markedly in 40mM K medium. In the presence of verapamil, the difference between the effects of Na removal and of Na readmission on Ca-induced contraction was markedly potentiated, particularly at 40mM K. It was concluded that the Na-Ca exchange mechanism may contribute to the transient response on Na removal and to the relaxation phase following Na readmission. At 5.9mM K, removal of Na may increase the Ca conductance and also reduce the contribution of prostaglandins. On the other hand, when depolarized by excess K, the effect of Na is less significant; probably due to a high Ca conductance.

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Venous CO₂ loading and/or unloading using an artificial lung was performed on dogs to evaluate whether changes in the rate of carbon dioxide output (V_CO2) can be involved in the control of respiration. As the signal providing V_CO2 information, small fluctuations in arterial P_CO2 (ΔPa_CO2) which synchronized with the respiratory cycle were estimated from both the mean Pa_CO2 and the fluctuations in arterial pH (ΔpH) measured with a catheter tip ISFET (ion sensitive field-effect transistor) pH sensor inserted in the common carotid artery. The open-loop method was used to analyze the effects of various respiratory parameters such as V_CO2, tidal volume, and respiratory frequency on the changes in ΔpH and ΔPa_CO2. Findings are: (1) ΔPa_CO2 was linearly proportional to V_CO2 while the correlation between ΔpH and V_CO2 was less linear, (2) magnitude of ΔpH was dependent on the changes in tidal volume while ΔPa_CO2 was not, (3) both the amplitude and the positive slope of Pa_CO2 oscillation were functions of respiratory frequency. These results suggest the possibility that if V_CO2 itself takes part in the control of ventilation, it will be CO₂ oscillation which links ventilation with V_CO2.

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To correlate changes in pacemaker frequency with those of length and tension in mammalian atrial tissues, a strip of the sinoatrial (SA) nodal tissue (about 10mm in length and 4mm in width) isolated from the rabbit heart was subjected to constant-length and constant-load stretches, and the relation between the resulting pacemaker frequency changes and the segmental length changes of the preparation was examined by means of cinematographic recording of the preparation with carbon markers on its surface. The amount of stretch-induced length changes was larger in the perinodal tissue segments than in the SA nodal segments, indicating that the nodal area is less extensible than the perinodal area. The time course of stretch-induced length changes of one nodal segment (closer to the inferior versa cava) was found to roughly parallel that of pacemaker frequency changes, suggesting that the pacemaker frequency is primarily dependent on the length but not on the tension of the SA nodal area.

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Influence of amino acids upon pancreatic exocrine secretion has been investigated in the isolated perfused pancreas of rats. Arg produced significant and dose-related inhibition of pancreatic juice flow, protein output and amylase output evoked by CCK-PZ (1.25pM). The secretory response evoked by CCK-PZ was inhibited by other amino acids (Ala, Asp, Asn, Gly, Ile, Leu, Lys, Met, Phe, Pro, Thr, Trp, Val, in each 20mM). A similar inhibitory pattern was observed using 10 mixed amino acids of 2mM each (Pro, Phe, Thr, Met, Lys, Asp, Leu, Trp, Val, Gly). Gly at a concentration of 20mM produced significant inhibition of exocrine secretion evoked by ACh (50nM) or GRP (36 pM). The inhibitory response induced by amino acids could not be repeated by using exogenous insulin (1μM) and glucagon (280nM). The inhibitory response was also not changed by increased extracellular Ca (5 or 10mM). However, Gly (20mM) produced inhibition of exocrine secretion evoked by Ca reintroduction into a pancreas which was pretreated with A 23187. It was suggested that the inhibitory effects of some amino acids on exocrine secretion are mainly caused by suppression of Ca influx in a stimulus-secretion coupling process.

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A significant DC-potential was recorded from the axon of shrimp myelinated giant nerve fiber, using a dye-filled microelectrode. Tracing of the dye assured that the source of the potential was the axonal membrane. All-or-none action potentials were obtained in the same preparation from which the ends of the axon were removed except for the synaptic region. It was concluded that the functionally excitable membrane is localized only in the synaptic region.

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Ag⁺ produced two different types of transient tension development in single frog toe muscle fibers in which the Ca²⁺ channel had been blocked by pretreatment with 2mM Co²⁺. These contractions were never observed in detubulated fibers, indicating that the Ag⁺-induced contraction is produced through Ca²⁺ channels located on the T-tubular membrane.

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In 11 cordotomized (C₂) rats with the vagi cut, monopolar electrical stimulation at a current intensity of 73±21 (S.E.) μA (n=6) to the intermediate region of the solitary nucleus elicited an increase (p<0.05) in regional blood flow (iodoantipyrine technique) of 71% and 43% in the frontal cortex and caudate nucleus, respectively. The findings suggest that some of the cardio-pulmonary and Cardio-vascular reflex mechanisms are involved in the regulation of the blood vessels of the brain.

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Noradrenaline (NA) evoked a contraction which consisted of two components, an initial one associated with only depolarization and a second one with spike discharges. Both contractions were abolished in a Ca-free solution leaving only small depolarization. In a Na-free solution, the initial contraction was increased in keeping with the short term depolarization, while the second contraction was abolished. It is suggested that NA initially causes Ca influx which secondarily increases Na permeability.

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