摘要:

AbstractTwo types of chloride current response to a step‐wise hyperpolarization of the toad skin is demonstrated: (1) An “instantaneous” response observed immediately upon voltage change, and (2) a subsequent slow response, the time course of which is sigmoidal. The slow response is due to an increase of a transcellular conductance which is specific to chloride ions. The time constant of the conductance increase is dependent on the amplitude of the transepithelial voltage displacement, the smallest time constants are obtained for the highest amplitudes and are in the order of 30 s. The voltage dependences of the steady‐state conductance and the steady‐state chloride current reveal that the chloride pathway has maximum conductance for V≅‐80 mV (outside of the skin being negative) and approaches a non‐conducting state for V>0 mV. This strong outward going rectification is a steady‐state phenomenon: In skins hyperpolarized for a few minutes, the “instantaneous” I‐V curves show that the chloride pathway in the conducting state allows a large inward chloride current (outward chloride flux) to pass in the voltage range 40 mV>V>0 mV. Calculations based on a three‐compartment model indicate that the strong steady‐state chloride current rectification cannot be obtained if only the intracellular chloride concentration and the membrane potentials are allowed to vary (“Goldman‐rectification”). It is suggested, therefore, that the permeability of the chloride pathway varies reversibly with the transepithelial potential difference. The variable which controls the chloride permeability may be a membrane potential or the conc

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06041.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractSubstitution of chloride in the outside bathing medium of the toad skin with bromide, iodide, nitrate and sulphate leads to a reduction in the apparent exchange diffusion of chloride across this tissue, and also to a reduction of the chloride current recorded during hyperpolarization. A series of inhibitors (thiocyanate, furosemide, phloretin, and acetazolamide) also affects chloride exchange diffusion, hyperpolarization current as well as chloride influx during hyperpolarization. Although in some cases, effects on short circuit current were also observed, none of the effects on chloride transport systems could be explained as secondary effects due to a primary interaction with the sodium transport mechanisms. A correlation was found between the clamping current recorded during hyperpolarization and the efflux of chloride under short circuit conditions with chloride Ringer's on both sides. On the basis of these findings, and the results reported in the previous paper (Hviid Larsen and Kristensen 1977) it is considered probable that the membrane molecules responsible for chloride exchange diffusion under short circuit conditions, are rearranged under the influence of a hyperpolarizing clamping voltage, thereby forming channels allowing charge transferring transport of chloride.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06042.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe effects of pindolol and sotalol on neuromuscular transmission were tested using intracellular micro‐electrode recording of resting membrane potentials, miniature end‐plate potentials and end‐plate potentials, and recording of muscle contractions upon nerve stimulation of rat phrenic nerve‐hemidiaphragm preparations. Both pindolol and sotalol reduced the amplitudes of miniature end‐plate potentials and end‐plate potentials in a dose‐dependent manner without significantly affecting their time‐courses. Pindolol, but not sotalol, also increased the frequency of the miniature end‐plate potentials and decreased the number of acetylcholine quanta released by nerve impulses. Neither of the drugs significantly affected resting membrane potentials of the muscle fibres or excitability of the motor nerve to ele

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06043.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe arterial baroreceptors were denervated in 20 normotensive Wistar rats. 2 1/2 months after the operation their cardiovascular responses to “mental stress” were compared to those of matched control rats (NCR). At the time of investigation the blood pressure of the baroreceptor denervated rats (BDR) was increased some 15 per cent above that of the control group. There was, however, no difference in response to “mental stress” between groups, if anything the BDR responded with less pronounced tachycardia. Two months subsequent to the stress‐test the mean blood pressure of the BDR was still significantly above normal levels, but the BDR did not exhibit structural cardiovascular adaptation, which has been documented in most types of stable hypertension as a response to the increased mean blood pressure. The results imply that hypertension induced by baroreceptor denervation is not of a stable and persistent type in which case structural changes in the cardiovascular system would have developed within the observation period (approximately 4 months). Emotional stimuli, however, do not seem to contribute to periodic blood pressure increases at the time of measurement, as earlier

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06044.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe crude mitochondrial fraction P2and subfractions of P2were prepared from the brain stem, hemispheres and whole brain of 19‐day‐old fetal rats. Samples were fixed in glutaraldehyde‐osmium, NaMnO4or by Tranzer's triple fixation method (aldehyde‐chromate‐dichromate‐osmium) and examined by electron microscopy. The C‐fraction from whole brain was the main synaptosome fraction, containing 3.2 % presynaptic terminals as counted from all membrane bound particles. The brain stem showed more presynaptic terminals than the hemisphere (2.8% versus 0.9%) suggesting a caudal‐rostral maturation gradient for synaptogenesis. The maturity of the nerve endings obtained was very variable in contrast to the rather uniform synaptosomes derived from adult tissue. They varied from profiles without any substructures to mature synaptosomes displaying asymmetric synaptic junctions. Monoamine synaptosomes containing small granular vesicles were not detected in the present study, suggesting immaturity of the granular monoamine pool at this stage

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06045.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe effect of moderate hypoxia (50.5 kPa air) and severe hypoxia (40.8 kPa air)in vivoon liver and heart triglyceride concentration and mitochondrial respiration rates was studied. Liver triglyceride concentrations increased in severe hypoxia from 7.3 μmol/g wet weight to 23.3 μmol/g wet weight over 7 days. After the period of seven days in severe hypoxia, the palmitate, octanoate and palmitoylcarnitine oxidation rates of mitochondrial suspensions were significantly reduced when the citric acid cycle was operative. No decrease in the fatty acid, fatty acyl‐CoA or carnitine derivative oxidation was observed when only the β oxidation system was studied. Mitochondria isolated from the heart or liver after seven days in severe hypoxia showed reduced respiratory control ratios, the decrease being from the normal 4.9 to 1.9 in the liver mitochondria using succinate as substrate. The reduction in respiratory control was mainly due to lowered State 3 respiration rates. Some reduction in the ratio was also observed in the fasting controls, from 5.8 to 3.4 with succinate. The respiratory control ratio could be partially normalized by the addition of albumin to the isolation medium for the liver mitochondria after severe hypoxia. Under these conditions, however, the State 4 respiration of the mitochondria from the hypoxic animals was higher than that for the cont

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06046.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractAn equation of two exponential terms was found to adequately describe the efflux of phenylalanine and tryptophan from cerebral cortex slices of adult and 7‐day‐old rats. These exponential terms described two forms (components) of efflux taking place at different rates. The fast component of efflux was more prominent in the slices from young rats than in those from adults. In both age groups the contribution of the fast component increased with an increasing amino acid concentration in the superfusate, but there were no changes in the rate constants. The rate constants of the fast components were equal in all experimental conditions in both age groups. The rate constants for the slow components of both amino acids were lower in the slices from adult rats than in those from young rats. The reason for efflux occurring at two different rates is discussed. The fast component probably consisted of the amino acid originating from the extracellular space of the slices and of the intracellular amino acid released by exchange. The slow component consisted of the amino acid released from the cells by other mechanisms, e.g. by diffusion through the membranes or by some active efflux processes. The cerebral cortex slices from adult rats have greater ability to concentrate aromatic amino acids than the slices from young rats. This may partly be dependent on the more effective influx and partly on the slower efflux of amino acids in the slices from adu

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06047.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe participation of aortic nerve C fibres in the baroreflex was investigated by recording changes in renal nerve activity in response to acute increases in arterial pressure, in two experimental situations: with the A and C fibres of the left aortic nerve intact, and with the A fibres temporarily blocked by a hyperpolarizing current (anodal block). Pressure was increased by manual inflation of an intra‐aortic balloon, and interference from other baroreceptor areas was avoided by carotid occlusion and sectioning of the right aortic nerve. Rises in mean arterial pressure exceeding 20 mmHg, to levels above 110 mmHg, were needed to trigger sympathetic inhibition via C fibres. A rise of 45 mmHg caused 50% reduction in sympathetic activity, equal to that obtained by stimulation of aortic nerve C fibres at about 3 Hz. In contrast, a rise of 20–30 mmHg evoked more than 60% reduction in sympathetic activity when the A fibres were operative. Judged by these studies of peak reflex responses to brief pressure rises, baroreceptors with C fibres in the aortic nerve have a much higher threshold to pressure than their myelinated counterparts; the C fibres contribute to the baroreflex inhibition of sympathetic discharge only when pressure is increased well above normal resting levels.Preliminary presentations of this paper were given in June 1976 at the 7th European Congress of Cardiology, Amsterdam, The Netherlands, and at the 8th Nordic Hypertension Meeting, Marstrand, Sweden (Aars, Myhre and Haswell 19

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06048.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractA cryoscopic technique has been developed that makes it possible to determine tissue osmolality in the core of the intestinal villi. During absorption from an isotonic electrolyte solution containing glucose an osmolality gradient was demonstrated from tip to base of the villi in both the jejunum and the ileum. The tissue osmolality at the villous tips was measured to 1 000–1 200 mOsm/kg H2O while the osmolality at the villous bases was approximately isotonic with plasma. Increasing intestinal blood flow by i.a. administration of a vasodilator drug, or making the intestine ischemic by clamping the intestinal vascular supply while supplying the mucosa with oxygen, markedly decreased tissue osmolality. Substituting all sodium ions with choline in the luminal perfusate abolished almost completely the tissue hyperosmolality and the intestine became a secretory organ. These observations are consistent with the view that the observed villous tissue hyperosmolality was created by a countercurrent multiplication of sodium chloride. The physiological implications of this mechanism is discussed and it is, among other things, proposed that the hyperosmolar region represents the hyperosmotic compartment necessary for explaining intestinal water absorptio

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06049.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe single injection indicator diffusion method for estimation of capillary diffusion capacity (Crone 1963) has been developed to provide directly visualized, continuous colorimetric recordings of the venous time‐concentration curves by means of a two‐colour densitometer system. Cardio‐Green, bound to albumin, is used as the non‐permeant (“reference”) tracer and Cr‐EDTA as the permeant one. The artificially perfused hindquarter muscle vascular bed of rats is used. Highly reproducible curve recordings can be obtained every fourth minute. Accidental disturbances of the recordings are readily detected. Thus, compared to the fractional venous sampling technique, the present technique has the great advantage of allowing immediately controlled and frequently repeated determinations of capillary diffusion capacity. It is therefore easily used together with measurements of filtration‐absorption events,e.g.for frequent quantitative comparisons of capillary diffusion and filtration capacities over a wide range of induced changes in perfused capillary surface area and/or capillary permeability. The main limitation is that the employed permeant tracer necessitates the use of erythrocyte

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1978.tb06050.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY