Technical note about simultaneous recording of oxygen partial pressure and neuronal activity in cat cortex.

A method is described for simultaneous measurements of pO2 and action potentials with microelectrodes using prefabricated gold wires. The construction and measuring with such gold electrodes is easier than with traditionally used platinum electrodes. Single electrodes recording is done with a specially adapted electronic circuit, allowing the separation of both signals (pO2 and action potentials. A measurement in cat brain illustrates this procedure.     

Eine sauerstoffundurchlässige Zone in der Wand der Arteria carotis der Katze

Summary By means of local pO₂ measurements with Pt-needle electrodes an oxygen impermeable zone in the arteria carotis of the cat has been found.     

Is there a critical tissue oxygen tension for bioenergetic status and cellular pH regulation in solid tumors?

Bioenergetic and metabolic status have been correlated with tissue oxygenation in murine fibrosarcomas (FSaII) of varying sizes (44–600 mm³). Ratios of -nucleoside triphosphates to inorganic phosphate (NTP/P_i) and phosphocreatine to inorganic phosphate (PCr/P_i) ratios derived from³¹P nuclear magnetic resonance spectroscopy (NMR) were positively correlated to median tissue O₂ tension (pO₂) values using O₂-sensitive needle electrodes. pH declined during growth with intracellular acidosis being evident in tumors >350 mm³. Whereas lactic acid formation greatly contributed to this decline in small and medium-sized tumors, adenosine triphosphate (ATP) hydrolysis and slowing down of the activities of pumps involved in cellular pH regulation seem to be major factors responsible for intracellular acidification in bulky tumors. PCr levels decreased at an early growth stage, whilst ATP concentrations dropped in bulky malignancies only, coinciding with a decrease in adenylate energy charge and a substantial rise in the levels of total P_i On average, median pO₂ values of ca. 10 mmHg represent a critical threshold for energy metabolism. At higher median O₂ tensions, levels of ATP, phosphomonoester (PME) and total P_i were relatively constant. This coincided with intracellular alkalosis or neutrality and stable adenylate ratios. On average, median pO₂ values <10 mmHg coincided with intracellular acidosis, ATP depletion, a drop in energy charge and rising P_i levels.     

Phosphocreatine and ATP concentrations increase during flow-stimulated metabolism in a non-contracting muscle

The gracilis muscle was excised from cold-acclimated rats, placed in vitro, and simultaneously perfused via its artery by high pO₂ medium and superfused by low pO₂ medium. With a doubling of the perfusion rate (from 50 to 100 μl/min) phosphocreatine and ATP increased by 39% and 44%, respectively.     

Corrélations électriques auriculo-ventriculaires dans le cœur ouvert en suspension de Grenouille

Summary (1) When in air, a quasi-dielectric medium, the frog's heart, opened in extension, emits auricular potentials which are detected on the ventricular track and conversely. (2) Polarographic tests for pO₂ changes in such a preparation, enclosed in a special moist box, show no variations; predominant anaerobiosis in heart or size of the box has to be considered.

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Travail réalisé sous contrat de la Délégation générale à la Recherche scientifique et technique (Convention 63-FR-071).     

Zur wirkung hypertoner Lösungen auf die markhaltige Nervenfaser

Summary The effect of hypertonic solutions on the action potential of single myelinated nerve fibres is described. Hypertonicity mainly changes the duration of the action potential: Short action potentials obtained in normal Ringer's solution at room temperature are prolonged, long action potentials due to 0.1–1.0 mM NiCl₂-Ringer's solution and low temperature are shortened by hypertonicity. The changes in action potential duration are accompanied by small changes in action potential amplitude. In addition, hypertonicity reduces the depolarization produced by 20 mM KCl; inactivation of the sodium-carrying system under cathodal polarization is enhanced.

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Die Untersuchungen wurden mit Unterstützung der Deutschen Forschungsgemeinschaft ausgeführt.     

Evaluation of O2 availability during glucose transport in everted sacs of rat small intestine

Riassunto Misurando il consumo di O₂ in funzione della pO₂ nel mezzo di incubazione è stato dimostrato che i sacchetti di intestino tenue rovesciato di ratto si trovano in condizione di parziale anaerobiosi nel corso dell'incubazione in liquido fisiologico contenente glucoso. Ciò viene posto in relazione con la notevole produzione di acido lattico da parte dell'intestino isolato mantenuto in tali condizioni.     

Calcium ionophore plus excision induce a large conductance chloride channel in membrane patches of human colon carcinoma cells HT-29cl.19A

In excised inside-out membrane patches of the human colon carcinoma HT-29cl.19A cells a large conductance (373±10 pS) chloride channel was found. Channel activity could only be observed after excision of patches from cells incubated with calcium ionophore. The channel was never observed in cell-attached patches. The channel was strongly voltage dependent, being open only between +30 and –30 mV clamp potentials. The selectivity sequence among anions, deduced from reversal potentials, was I>Br>Cl>F>gluconate. The P_Na/P_Cl was 0.09. Although a similar type of channel, has been described earlier, this is the first report stating its appearance in patches of intestinal epithelial cells requiring the combined action of Ca²⁺ ionophore and excision, suggesting its control by an intracellular compound.     

The response of Ca-mediated action potentials and contractile activity in mammalian ventricular myocardium towards alkalosis

Summary Alkalosis (pH 7.8) produced by reduction of CO₂ concentration augmented both upstroke velocity of Ca action potentials and isometric contractile force of mammalian heart muscle. If the increase of pH to 7.8 was achieved by a raise of HCO₃ concentration (with simultaneous reduction of CO₂ concentration), the positive inotropic response was not accompanied by an augmented Ca current. Obviously, the well-known positive inotropic effect of alkalosis does not only depend upon the enhancement of transmembrane Ca influx during excitation, but can be mediated alone by affecting intracellular Ca movements as well.     

Zinc antagonizes the effect of botulinum type A toxin at the mouse neuromuscular junction

Summary Zn²⁺ (10–100 M) elevated the frequency of miniature end-plate potentials (MEPPs) in the mouse diaphragm. The effect did not depend on external Ca²⁺. Botulinum type A toxin (BTX_A, 50 ng/ml) abolished MEPPs almost completely within 30 min. Zn²⁺ (100 M) restored MEPPs and increased their frequency after they had been abolished by BTX_A in Ca²⁺-free solutions. The antagonistic effect of Zn²⁺ in the Ca²⁺-free solution was reduced by exposing the diaphragm to the toxin in the Ca²⁺-free solutions containing high K⁺. Thus, the action of BTX_A is probably enhanced by depolarization of the motor nerve terminals.     

Frequency-dependent effect of verapamil on rat soleus muscle

Summary In the presence of verapamil (0.1 mM) rat soleus muscle fibers failed to generate action potentials with overshoots. In fibers with their V_m set to a local level of –90 mV, verapamil produces a gradual reduction in the amplitude of the repetitive action potentials; this effect is more pronounced at high rates of stimulation (100 Hz). Our results suggest a local anesthetic action of this drug that could contribute with its calcium channel blocking effect to the diminished mechanical tension observed in the presence of the drug.Acknowledgments. We thank A. Losavio and M. Stefanolo for technical assistance. This work was supported by grants from CONICET and SUBCYT, Buenos Aires, Argentina and Muscular Dystrophy Association, USA.     

Action de l'eau oxygénée sur un anaérobie strict

Summary A quantitative study on the action of H₂O₂ uponCl. saccharobutyricum shows that the primary action is produced upon a first substance X, very likely an enzyme, following a mechanism such as one equivalent of oxygen gives a reversible combination, and two equivalents an irreversible combination.     

Sodium and calcium action potentials in human anterior pituitary cells

Summary Human anterior pituitary cells derived from a somatotropin-secreting adenoma were capable of generating action potentials with Ca²⁺ and tetrodotoxin-sensitive Na⁺ components. A major fraction of the action current was carried by Na ions.We wish to thank Dr O. Sand for correcting the English and Miss Michiko Takano for technical assistance. We also acknowledge the collaboration of Dr S. Miyazaki in the electron microscope.     

Ionic mechanisms in pancreatic β cell signaling

The function and survival of pancreatic β cells critically rely on complex electrical signaling systems composed of a series of ionic events, namely fluxes of K⁺, Na⁺, Ca²⁺ and Cl^? across the β cell membranes. These electrical signaling systems not only sense events occurring in the extracellular space and intracellular milieu of pancreatic islet cells, but also control different β cell activities, most notably glucose-stimulated insulin secretion. Three major ion fluxes including K⁺ efflux through ATP-sensitive K⁺ (K_ATP) channels, the voltage-gated Ca²⁺ (Ca_V) channel-mediated Ca²⁺ influx and K⁺ efflux through voltage-gated K⁺ (K_V) channels operate in the β cell. These ion fluxes set the resting membrane potential and the shape, rate and pattern of firing of action potentials under different metabolic conditions. The K_ATP channel-mediated K⁺ efflux determines the resting membrane potential and keeps the excitability of the β cell at low levels. Ca²⁺ influx through Ca_V1 channels, a major type of β cell Ca_V channels, causes the upstroke or depolarization phase of the action potential and regulates a wide range of β cell functions including the most elementary β cell function, insulin secretion. K⁺ efflux mediated by K_V2.1 delayed rectifier K⁺ channels, a predominant form of β cell K_V channels, brings about the downstroke or repolarization phase of the action potential, which acts as a brake for insulin secretion owing to shutting down the Ca_V channel-mediated Ca²⁺ entry. These three ion channel-mediated ion fluxes are the most important ionic events in β cell signaling. This review concisely discusses various ionic mechanisms in β cell signaling and highlights K_ATP channel-, Ca_V1 channel- and K_V2.1 channel-mediated ion fluxes.     

The action of the peptidoleukotriene LTD4 on intracellular calcium in rat mesangial cells

The dose-dependent effect of CGP 45715A on the LTD₄-induced Ca²⁺ response of glomerular mesangial cells has been studied. Our results demonstrate that the LTD₄-dependent increase in the cytosolic Ca²⁺ concentration primarily involves an InsP₃-mediated release of Ca²⁺ from intracellular storage sites and to a minor extent an enhanced influx of Ca²⁺ through receptor-operated Ca²⁺ channels located in the plasma membrane. The action of CGP 45715A on the Ca²⁺ response is an inhibitory one and is convincingly explained by a displacement of LTD₄ from its receptor site(s). The contractile effect of LTD₄ on pulmonary smooth muscle is proposed to be mainly caused by a receptor-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate.     

Electrical uncoupling by Sr action potentials in cardiac muscle

Summary Sr action potentials elicited in guinea-pig papillary muscle under Na-free conditions decreased the space constant and increased the input resistance. It suggests that Sr current induced intercellular uncoupling by increasing [Sr]_i.Supported by grant from Japanese Ministry of Education and from Japan Heart Foundation Research Grant for 1976 contributed by Tokyo Marine and Fire Insurance Co., Ltd.     

Effect of platelet activating factor on guinea-pig papillary muscle

Summary Platelet activating factor (PAF) induces a biphasic effect on guinea-pig papillary muscle: 1. a transient positive inotropic effect preceded by an increase in action potential duration (APD); 2. a marked negative effect on inotropism and on APD. Since Ca⁺⁺ slow action potentials were initially enhanced by PAF and then markedly depressed, it is suggested that PAF specifically interferes with the Ca⁺⁺ slow channel.     

Electrophysiological actions of chlorimipramine on guinea-pig ventricular fibres

Summary Chlorimipramine (CMI, 1×10^–5M to 7×10^–5M) decreased the amplitude, overshoot and rate of rise of ventricular action potentials and abolished the Ca-mediated action potentials elicited in guinea-pig papillary muscles. These results indicates that CMI inhibits the rise in sodium and calcium conductances during the cardiac action potential.     

The dimeric and co-operative myoglobin ofNassa mutabilis. A peculiar case

The myoglobin present in the radular muscle of the Prosobranchia sea snailNassa mutabilis is a peculiar case among myoglobins. It is a dimer showing co-operative oxygen binding equilibrium curves with pO_{2 1/2}=4.7 mmHg, invariant with pH, and n=1.6. Although the globin is composed of 147 amino acid residues, corresponding to a molecular mass of 15760 D, gel filtration chromatography of the native myoglobin indicate Mr=26000±2000 D. Similarly, acrylamide electrophoretic analyses in SDS and velocity sedimentation indicate a molecular mass of about 13000 D for the denatured globin. The molecule is highly unstable and forms slowly a chromogen when aged or immediately upon oxidation to the ferric state. The visible region of the absorption spectrum of the O₂ or CO liganded myoglobin derivatives indicate an altered heme environment. Circular dichroism analyses confirm this indication showing negative Cotton effects in all regions of the heme absorption spectra of the MbO₂ and MbCO derivatives. Interestingly, the CD spectrum of the oxidised met-form shows a positive band almost symmetrical with respect to that of the MbO₂ derivative. This is similar to what reported for the monomeric hemoglobin ofGlycera dibranchiata for which a reversed heme orientation was proposed. Detailed resonance Raman spectroscopic studies have permitted a more direct investigation of the interactions between the heme and the protein. The proximal Fe-Im bond shows a stretching mode frequency down shifted by 5 cm^–1 with respect to the corresponding band of horse heart myoglobin, in good correlation with the much higher instability ofNassa m. myoglobin and its much lower oxygen affinity. The unusual bond instability finds additional support in a kinetic study in which the myoblogin is mixed with CO in buffered solutions at different pH values. This approach gives evidence that the Fe-Im bond is broken upon lowering the pH, with a pK of 4.0±0.2, the highest among those of deoxy hemoproteins. The rupture of the proximal bond appears to occur with a proton-linked transition showing n=1.8±0.1, again indicating cooperativity between the two subunits. The vinyl and propionate heme substituents show resonance Raman spectroscopic bands indicating different modes of interaction with their environment with respect to other myoglobins. Most interestingly, the vinyl stretching mode frequency, typically a single band, appears split in two bands inNassa m. myoglobin. This splitting is evident in all the investigated derivatives of the myoglobin, indicating that vinyl 2 and 4 are not equivalent in this molecule. A similar splitting has been found so far only inChironomus t.t. hemoglobin.     

Über die Wirkung blutzuckersenkender Sulfonylharnstoffe auf das isolierte Rattenzwerchfell

Summary The action of blood sugar depressing sulfonylureas on glucose and oxygen uptake, as well as on glycogen content and formation of C¹⁴O₂ from uniformly labelled C¹⁴-glucose was investigated in rat hemidiaphragms incubated in phosphate buffer. The following results were obtained: (1) Tolbutamide and Carbutamide increased the glucose uptake. (2) Tolbutamide decreased the glycogen-content. (3) Oxygen uptake as well as formation of C¹⁴O₂ were increased by Tolbutamide. (4) The action of Tolbutamide and insuline was equal with respect to glucose uptake but different as regarding the glycogen content, oxygen uptake and CO₂-formation.It is concluded that sulfonylureas increase glucose oxidation in the rat hemidiaphragm probably without increasing insulin sensitivity. To our knowledge this mechanism of action has hitherto not been described.