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Biomedical subjects

H Acker

Publications and source records attributed to H Acker.

At least 109 records · Page 6Linked to original sources
PubMed1980

Relationship between tissue po2 and chemoreceptor activity of the carotid body in vitro.

Tissue pO2 (pgO2) and sinus nerve activity were recorded in the carotid body in vitro under hypoxic conditions produced either by interrupting the superfusion flow or by lowering the pO2 of the medium (pmO2). The pgO2 gradient is the steeper the higher pmO2 is. These findings point to a pO2-dependent oxygen consumption. Under hypoxia produced by interrupting the superfusion flow, pgO2 declines slowly down to final values and, concomitantly, the chemoreceptor discharge increases. Under hypoxia produced by lowering pmO2, pgO2 decreases rapidly down to values of about 3 torr, whereas the chemoreceptor discharge at first increases and then decreases, in spite of a maintained low pgO2. The pO2 threshold where the chemoreceptor starts firing under hypoxia, varies between 9 and 90 torr.

Animals↗
PubMed1980

Distribution of oxygen partial pressure in the carotid body region and in the carotid body (rabbit).

In the specific tissue of the rabbit carotid body as well as in the connective tissue surrounding the organ, pO2 distribution was measured with membrane-covered needle electrodes (tip diameter 1-2 microns). The histograms resulting from measurements in the specific tissue were shifted to low pO2 values as compared to other tissues. The oxygen blowing test, i.e. exposure of the carotid body to humidified 100% oxygen was employed to decide upon the site of measurement: pO2 increased when the electrode measured in the surrounding tissue (type 1 response); pO2 remained stable or slightly decreased when the electrode sampled in the specific carotid body tissue (type 2 response). After the experiment, the electrode track was reconstructed from histological serial sections and the type of reaction was related to the type of tissue. Low pO2 values were found to prevail in the specific carotid body tissue, which leads to the conclusion that the amount of low pO2 values determines the degree of chemoreceptor activity.

Animals↗
PubMed1980

The meaning of tissue pO2 and local blood flow for the chemoreceptive process of the carotid body.

The paper concentrates on measurements of tissue pO2 and local flow, which are both assumed to determine the nervous signal of the carotid body. The measurements were performed with needle electrodes. Inside the specific tissue of the carotid bodies of cat and rabbit, which is assumed to be surrounded by an oxygen barrier, pO2 values between 7 and 25 torr were recorded. From experiments on the fetal carotid body it was concluded that these low values are essential for the chemoreceptive process. Two types of blood flow were observed in the carotid body: high flow running through arteriovenous shunt vessels or flow-through channels (total flow), and low flow running through the capillaries supplying the specific tissue (local flow). Local flow decreases under hypoxia, whereas total flow follows the changes in blood pressure in any case. These pO2-dependent regulatory mechanisms influence the extracellular calcium activity, which determines the calcium uptake of type I cells under hypoxia and, consequently, (by vesicle release) the chemoreceptor discharge. Other mechanisms are assumed to be involved during hypercapnia, since under these conditions local flow does not change.

Animals↗
PubMed1980

Measurements of the partial pressure of oxygen in the carotid body of fetal sheep and newborn lambs.

The partial pressure of oxygen in chemoreceptors tissue of the carotid body was measured in parallel with arterial oxygen tension in eleven sheep fetuses exteriorized from 9 ewes anaesthetized with pentobarbitone, in 6 of these fetuses in the transitional period following occlusion of the umbilical cord and the start of artificial pulmonary ventilation and in 6 naturally born lambs, 10-36 h old. In the fetal carotid body, O2 gradients were very small and, in the majority of tests, the arterial-to-tissue O2 difference was small or negligible. During the transitional period, this difference increased as arterial PO2 rose and in the newborn lamb, this difference was as large as that reported in the adult carotid body. These results indicate that in the fetal carotid body, the levels of blood flow and metabolism are likely to be homogeneous and that the ratio of O2 supply and O2 consumption is high, that in the transitional period and in the newborn, either O2 supply falls or O2 consumption increases or both, and that these changes are both O2-dependent and persist although arterial PO2 in the newborn is reduced to or close to fetal levels. The possible mechanisms are discussed.

Aged↗
PubMed1980

Double-barrell ion-sensitive microelectrodes with extra thin tip diameters for intracellular measurements.

A method has been described by which double-barrel ion-sensitive microelectrodes for intracellular measurements can be produced with a mean tip diameter of 0.1 micron. Potassium, calcium and chloride activity could be measured with these electrodes by means of ion exchangers and neutral ion carriers. The mean steepness for the potassium electrode is 50.16 mV, for the calcium electrode 24.7 mV and for the chloride electrode 39 mV. the drift of the electrodes varies between 2-4%/h. The mean response time amounts for the potassium electrode to 170 ms, for the calcium electrode to 350 ms and for the chloride electrode to 250 ms. With these electrodes it is possible to measure intracellularly cell membrane potential and ion activity simultaneously.

Action Potentials↗
PubMed1979

A PCO2 surface electrode working on the principle of electrical conductivity.

A PCO2 electrode working on the principle of electrical conductivity is described. The calibration curve can be linearized according to the formula G = Go + b square root PCO2. This linearity has been tested in the PCO2 range of 0.93-9.33 kPa (7--70 Torr). For the experiments electrodes are used which have conductivity values of about 50 nS and drifts of maximally 5%/h at a PCO2 of 5.33 kPa (40 Torr). The response time (T90) is about 20 s. The temperature sensitivity is 2.4 nS/1 K between 298 K-310 K. The standard error of the measurements is sigma = 0.33 nS. With these electrodes tissue PCO2 can be measured on the surface of various organs.

Carbon Dioxide↗
PubMed1979

[Quantitative determination of the vascular volume of the cat carotid body under normoxia, hyperoxia, hypoxia and hypercapnia (author's transl)].

The ratio vascular volume to total volume was quantitatively analyzed in the cat's carotid body in dependence on the oxygen content of respired air and arterial pO2, respectively. Under hypoxia the vascular volume was 50% higher than under hyperoxia. This connection was ascertained after both perfusion fixation and immersion fixation.

Animals↗
PubMed1978

Measurements of potassium changes in the cat carotid body under hypoxia and hypercapnia.

With the aid of potassium-sensitive microelectrodes reinforced by bitumen (tip diameter, 1.5 micrometer), extracellular potassium activity ([K+]e) and DC potential were measured in the cat's carotid body. Under normoxic and normocapnic conditions, potassium values of 1--16 mM (mean value 7.2 mM, standard deviation 3.8 mM) and DC potential values of -11 mV to + 13 mV were recorded. With hypoxia, [K+5e increased by between 1 mM and 9 mM; DC potential was reduced by between 0.5 and 3 mV. With hypercapnia, [K+]e decreased by between 1 mM and 5 mM changes in DC potential were variable. The results suggest that, during hypoxia potassium influences the nervous structures in the carotid body whereas this influence is absent during hypercapnia.

Animals↗
PubMed1976

Oxygen transport capacity of the capillary blood within the carotid body.

Local deltaPo2 deltat in the carotid body after perfusion stop depends on the oxygen consumption of the tissue and the apparent O2 solubility coefficient alpha of the blood. Oxygen consumption of the carotid body tissue can be determined by measuring the local deltaPo2 deltat with Po2 needle electrodes after Krebs-Henseleit perfusion. Assuming the same deltaPo2 deltat for the blood-perfused carotid body the actual Po2 decrease can be used to estimate the hemoglobin content of the tissue. The influence of hemoglobin is described by the factor alpha/alpha. Control values measured in the Krebs-Henseleit-perfused carotid body yielded values of alpha/alpha = 0.8-3. In a series of 11 blood-perfused carotid body preparations with 105 perfusion stops the quotient alpha/alpha changed with arterial Po2. At Po2 values higher than 100 Torr alpha/alpha was between 0.8 and 2. This value thus was in the same range as the control values. Below 100 Torr higher values up to 11 were observed. Since a blood-perfused tissue (15 g% Hb) would have an alpha/alpha of about 128, we conclude that the carotid body is mainly perfused by plasma, and that with decreasing arterial Po2 more red cells flowed through the carotid body.

Animals↗
PubMed1976

[Glomus caroticum. A model to understand chemoreception].

To understand the chemoreceptive process of the carotid body we have investigated under which conditions the chemoreceptor is stimulated and which part is taken over by its different cell elements in this process. In this way it was possible to open the "black box" as Torrance called the carotid body to prove all the hypotheses and models about the chemoreception in the carotid body.

Animals↗