bluuebunny/crossref_metadata_2025 huggingface dataset:
Blood flow to and the metabolism of glucose and lactate by the liver in vivo in fetal, newborn and adult sheep.
Authors: Apatu R S , Barnes R J
Published: December 2014

1. The blood flow to the liver in fetuses near to term, in newborn and in adult sheep was measured in vivo by the Fick principle using radionuclide‐labelled plastic microspheres and timed withdrawal of reference organ blood samples. 2. There is a rapid flow of blood, 410.1 +/‐ 41.8 ml min‐1 (100 g liver)‐1, mean +/‐ S.E.M., to the liver in the fetus. Immediately after birth the blood flow is significantly less (172.5 +/‐ 27.5 ml min‐1 (100 g liver)‐1), reflecting the loss of the umbilical venous return to the liver following delivery and separation from the placenta. Arterial blood flow to the liver per unit weight of liver was small in the fetus (9.5 +/‐ 1.2 ml min‐1 (100 g liver)‐1), significantly greater in the immediate newborn (27.9 +/‐ 7.9 ml min‐1 (100 g)‐1) but appeared to decline with age after birth to 12.2 +/‐ 6.6 ml min‐1 (100 g)‐1 in lambs at 16 weeks of age. Portal blood flow to the liver, on a weight basis, changed little with age being 126 +/‐ 20.9 ml min‐1 (100 g liver)‐1 in the fetus, 144.7 +/‐ 21.1 ml min‐1 (100 g liver)‐1 in the immediate newborn and 203.2 +/‐ 27.8 ml min‐1 (100 g liver)‐1 in the adult. 3. Oxygen consumption and glucose and lactate fluxes across the sheep liver were determined from 132 days of gestation into adulthood. 4. The oxygen consumption by the fetal liver was 0.11 +/‐ 0.02 mmol min‐1 (100 g)‐1 which represents about 6% of the total fetal oxygen metabolism. Immediately after birth there was an apparent increase in liver oxygen consumption but the wide variation in the values recorded means that the change is not statistically significant. There were no significant changes in liver oxygen consumption with age after delivery, oxygen consumption by the adult liver was 0.16 +/‐ 0.05 mmol min‐1 (100 g)‐1. 5. The liver at all ages studied consumed lactate. Lactate consumption was particularly high in the fetus (0.13 +/‐ 0.04 mmol min‐1 (100 g)‐1 and could account for three times the oxygen consumed by the fetal liver, but the fate of this lactate is not yet known. 6. In the fetus the liver is in approximately zero glucose balance; in contrast postnatal animals release glucose from the liver at rest.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanisms underlying intracellular signal transduction of the slow IPSP in submucous neurones of the guinea‐pig caecum.
Authors: Mihara S , Hirai K , Katayama Y , Nishi S
Published: December 2014

1. Intracellular recordings were obtained from submucous plexus neurones of the guinea‐pig caecum. 2. The resting membrane conductance displayed two types of inward rectification: one which developed at potentials more negative than ‐70 mV, and another that occurred at potentials more negative than the potassium equilibrium potential. The former inward rectification was blocked by extracellular caesium (Cs+; 1‐2 mM) and the latter was blocked by Cs+ (1‐2 mM) or barium (Ba2+; 30‐100 microM). 3. The noradrenaline‐induced current measured by subtraction of the current‐voltage (I‐V) relation before and after adding the agonist also showed an inward rectification around the resting potential. Ba2+ (30‐100 microM) blocked both the outward and inward current induced by noradrenaline. The noradrenaline current was not affected by Cs+ (1‐2 mM). Both the slow IPSP and the slow IPSC (inhibitory postsynaptic current) were reduced by Ba2+, but not by Cs+. 4. During the intracellular injection of guanosine 5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S), multiple repetitive stimulation or repeated applications of noradrenaline produced irreversible membrane hyperpolarizations with a decreased membrane input resistance, until the membrane had approached the potassium equilibrium potential. 5. Pertussis toxin (1‐40 micrograms/ml) abolished both the slow IPSP and the noradrenaline hyperpolarization without affecting the nicotinic fast EPSP or the slow EPSP. 6. Superfusion with a Ca(2+)‐free, high‐Mg2+ (12 mM) solution caused a membrane depolarization associated with an increased input resistance. It eliminated the Ca2+ spikes, the slow after‐hyperpolarizations following the spikes, and the synaptic potentials within 3 min. Prolonged exposure (longer than 20 min) to this solution resulted in a progressive decline of the noradrenaline hyperpolarization. 7. Intracellular injection of ethylene glycol‐bis(beta‐aminoethylether)N,N,N',N'‐tetraacetic acid (EGTA) reduced the slow IPSP and the noradrenaline hyperpolarization. Superfusion with a membrane‐permeable Ca2+ chelator, 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid, tetraacetoxymethyl ester (BAPTA/AM; 10‐200 microM) reduced the noradrenaline hyperpolarization. 8. Procaine reversibly reduced the slow IPSP and noradrenaline hyperpolarization without affecting the fast EPSP or slow EPSP at concentrations up to 300 microM.(ABSTRACT TRUNCATED AT 400 WORDS)
Novel chloride conductance in the membrane of bovine chromaffin cells activated by intracellular GTP gamma S.
Authors: Doroshenko P , Penner R , Neher E
Published: December 2014

1. The effects of introducing the non‐hydrolysable GTP analogue guanosine 5'‐O‐(3‐thiotriphosphate) (GTP gamma S) into perfused bovine chromaffin cells were studied by a combination of the tight‐seal whole‐cell patch‐clamp technique and Fura‐2 fluorescence [Ca2+]i measurements. 2. GTP gamma S (5‐300 microM) induced a slowly developing transient current (inwardly directed at the holding potential ‐60 to ‐70 mV) and [Ca2+]i oscillations. The current activated with a 10‐50 s delay after the start of whole‐cell dialysis, peaked at 70‐120 s and decayed almost to its initial level during the next 150‐300 s. Calcium oscillations were observed within the first 100‐150 s of cell perfusion. 3. GTP competitively lowered the probability of current activation by GTP gamma S. At low GTP gamma S/GTP ratio (5 and 300 microM, respectively) activation of the current was observed only rarely. 4. The activation of the current was accompanied by an increase in conductance but not by changes in the current reversal potential. The changes in the conductance did not depend on the membrane potential; no time‐dependent relaxation of the current was induced by steps in the membrane voltage. 5. The current reversal potential was close to the Cl‐ equilibrium potential; changes in the extracellular Cl‐ concentration induced corresponding changes in the current amplitude and shifted its reversal potential. The permeability to larger anions‐‐aspartate, glutamate and isethionate‐‐was about one‐tenth of that for chloride. 6. Single‐channel conductance, estimated from the ratio of the mean current and its variance, was about 1‐2 pS. 7. The current could be reversibly blocked by 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonate (DIDS, 10 microM), chlorpromazine (5 microM) and tolbutamide (0.5‐5 mM). 8. It is suggested that the GTP gamma S‐induced increase in the permeability to Cl‐ ions is due to a G protein‐mediated production of an as yet unidentified second messenger.
On the mechanism of nucleotide diphosphate activation of the ATP‐sensitive K+ channel in ventricular cell of guinea‐pig.
Authors: Tung R T , Kurachi Y
Published: December 2014

1. Effects of intracellular nucleotide diphosphates (NDPs) on the ATP‐sensitive K+ channel (K+ATP channel) were examined in ventricular cells of guinea‐pig heart, using the inside‐out patch clamp technique. On formation of inside‐out patches in the ATP‐free internal solution, the K+ATP channel appeared and then ran down spontaneously. This run‐down of the K+ATP channel activity was probably due to dephosphorylation. 2. Millimolar concentrations of various NDPs, e.g. UDP (uridine diphosphate), IDP (inosine diphosphate), CDP (cytidine diphosphate) and GDP (guanosine diphosphate), applied to the internal side of the patch membrane, induced openings of the K+ATP channel after run‐down, i.e. in the dephosphorylated state. ADP opened the channel weakly at low concentrations (100 microM) but inhibited it at higher concentrations (1‐10 mM). 3. NDP‐induced openings of the channel were Mg2+ dependent and inhibited by ATP (100 microM) and glibenclamide (1 microM). None of nucleosides, nucleotide monophosphates nor nucleotide triphosphates induced openings of the channel. Thus, the K+ATP channel may have a Mg(2+)‐dependent NDP‐binding site, which induces openings of the dephosphorylated channel in ATP‐free solution, in addition to the Mg(2+)‐independent ATP‐binding inactivation site and phosphorylation site. 4. In inside‐out patches, pinacidil (a K+ATP channel opener) activated the K+ATP channel in the phosphorylated state but not in the dephosphorylated state. In the presence of NDPs (UDP, IDP, CDP, GDP), however, pinacidil (30 microM) enhanced openings of the dephosphorylated K+ATP channel prominently. 5. From the above results, we concluded that NDP‐binding to the specific site has similar effects to channel phosphorylation, i.e. it keeps the K+ATP channel in an operative state in ATP‐free solution and enhances the pinacidil‐induced channel openings.
Atropine‐resistant submandibular responses to stimulation of the parasympathetic innervation in the anaesthetized ferret.
Authors: Tobin G , Ekström J , Bloom S R , Edwards A V
Published: December 2014

1. Submandibular salivary and vascular responses to stimulation of the peripheral end of the chorda‐lingual nerve at 20 Hz continuously for 60 min were investigated in anaesthetized ferrets, in which the sympathetic innervation to the gland was cut, in the presence and absence of atropine (2.0 mg kg‐1). 2. Both the increase in submandibular salivary flow and protein output, which occurred in response to nerve stimulation, were substantially reduced following the administration of atropine, the latency was greatly increased thereby, and both responses were more transient but neither was abolished by atropine. The fall in submandibular vascular resistance was not significantly affected by atropine, either in respect of extent or duration. 3. Chorda‐lingual stimulation produced an increase in the output of vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin gene‐related peptide (CGRP) in the submandibular venous effluent blood. Each of these responses was maximal within the first 10 min after the onset of stimulation and declined thereafter. The time‐scales of both the CGRP and SP responses were similar to those of the atropine‐resistant secretory responses, both being quite short‐lived, whereas the output of VIP (like the atropine‐resistant vascular response) was significantly greater than the basal value throughout the whole of the 60 min period of stimulation. 4. The CGRP response was completely abolished by pre‐treatment with atropine, whereas the outputs of both VIP and SP were significantly enhanced thereby. Both the submandibular vascular and secretory responses to chorda‐lingual stimulation were almost completely suppressed following the administration of hexamethonium, and there was then no detectable release of peptidergic agonists from the gland. 5. The atropine‐resistant submandibular salivary secretory responses were completely abolished by pre‐treatment with a tachykinin inhibitor [( D‐Arg1, D‐Cl2 Phe5, Asn6, D‐Trp7,9, Nle11]‐SP; 0.75 mg kg‐1) without affecting the fall in submandibular vascular resistance. 6. Following pre‐treatment with hexamethonium, I.V. bolus injections of methacholine, SP and CGRP elicited increases in submandibular blood flow and secretion of saliva. VIP caused an increase in blood flow without overt secretion, although it is known to increase secretion of protein and to potentiate the secretory response to SP. Taken together, all these results are consistent with the contention that VIP contributes to the vasodilator response to stimulation of the para‐sympathetic innervation in this gland and that both SP and CGRP are likely to contribute to the secretory response.
Diastolic, systolic and sarcoplasmic reticulum [Ca2+] during inotropic interventions in isolated rat myocytes.
Authors: Frampton J E , Orchard C H , Boyett M R
Published: December 2014

1. The fluorescent indicator Fura‐2 has been used to monitor intracellular [Ca2+] (Ca2+i) in myocytes isolated from the ventricles of rat hearts. 2. The relationships between diastolic Ca2+i, systolic Ca2+i and the Ca2+ content of the sarcoplasmic reticulum (SR; assayed using caffeine) have been studied during changes of stimulation rate and bathing [Ca2+] (Ca2+o). 3. When stimulation rate was increased, there were increases in diastolic Ca2+i, systolic Ca2+i and the Ca2+ content of the SR. 4. The SR inhibitor ryanodine (1 mumol l‐1) decreased the size of the Ca2+i transient, and abolished the increase of Ca2+i produced by caffeine (10 mmol l‐1). In the presence of ryanodine, increasing stimulation rate increased diastolic Ca2+i but not systolic Ca2+i. 5. Increasing Ca2+o led to increases of diastolic Ca2+i, systolic Ca2+i and SR Ca2+ content similar to those observed during changes in stimulation rate. 6. Ryanodine altered the relationship between systolic and diastolic Ca2+i during changes of Ca2+o. 7. These results are consistent with a change of diastolic Ca2+i leading to an increase in the Ca2+ content of the SR, and hence an increase in the size of the Ca2+i transient during changes in stimulation rate and Ca2+o.
GTP and noradrenaline‐induced force in isolated toxin‐permeabilized rat anococcygeus and guinea‐pig portal vein.
Authors: Crichton C A , Smith G L
Published: December 2014

1. Strips of smooth muscle from rat anococcygeus and guinea‐pig portal vein were treated with solutions containing crude alpha‐toxin from the bacterium Staphylococcus aureus. This rendered the surface membrane permeable to small molecular weight substances, but left functional sarcolemmal adrenoceptors. Tension measurements from these preparations were used to investigate the effects of guanosine‐5'‐triphosphate (GTP) on the noradrenaline‐induced Ca2+ release from the sarcoplasmic reticulum (SR) of the smooth muscle of rat anococcygeus and guinea‐pig portal vein. 2. Under conditions of low Ca2+ buffering (0.2 mM‐EGTA), applying a maximal dose of noradrenaline (30 microM) to a toxin‐permeabilized strip of anococcygeus muscle and longitudinal muscle of guinea‐pig portal vein caused a transient contracture. Subsequent exposures to noradrenaline resulted in progressively smaller contractures. However, the rate of decline in the size of the noradrenaline‐induced contracture was greater in rat anococcygeus muscle than in guinea‐pig portal vein preparations. The decline in the size of the contracture in toxin‐permeabilized anococcygeus muscle was not due to a fall in the Ca2+ content of the SR or a reduced Ca2+ release from the SR in response to myo‐inositol 1,4,5‐trisphosphate (IP3). 3. The tension transients due to noradrenaline were enhanced and maintained in the presence of 100 microM‐GTP in toxin‐permeabilized guinea‐pig portal vein. Addition of 100 microM‐GTP caused a transient contracture in permeabilized rat anococcygeus muscle and only promoted the next noradrenaline response, thereafter the amplitude of the contractures decayed to zero. 4. Addition of guanosine‐5'‐O‐(2 thiodiphosphate) (GDP‐beta‐S, 100 microM) would be expected to cause a reversible reduction of the noradrenaline response by binding to the intermediary G‐protein. This was observed in toxin‐permeabilized portal vein, but in rat anococcygeus muscle, GDP‐beta‐S caused slowing of the response to noradrenaline, thereafter the response to noradrenaline was absent. The noradrenaline response did not recover when GDP‐beta‐S was removed. 5. The non‐metabolizable form of GTP, guanosine‐5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S, 100 microM), caused a transient contracture in both toxin‐permeabilized rat anococcygeus muscle and guinea‐pig portal vein. In both these tissues, the addition of GTP‐gamma‐S resulted in the irreversible inhibition of the response to noradrenaline. 6. In the presence of a high concentration (10 mM) of the Ca2+ buffer EGTA, GTP (100 microM) and noradrenaline (30 microM) increased Ca(2+)‐activated force in both tissues.(ABSTRACT TRUNCATED AT 400 WORDS)
Different types of glutamate receptors in isolated and identified neurones of the mollusc Planorbarius corneus.
Authors: Bolshakov V Yu , Gapon S A , Magazanik L G
Published: December 2014

1. The membrane currents evoked by glutamate agonists on isolated and identified neurones of molluscan pedal ganglia were investigated using the voltage clamp technique. 2. The fast chloride current (Er (reversal potential) = ‐41 mV) evoked in a Ped‐9 neurone by application of glutamate, quisqualate and ibotenic acid could be blocked by furosemide (0.1 mM). The slow potassium current (Er = ‐85 mV) evoked in Ped‐8 and Ped‐9 neurones by glutamate, quisqualate and kainate could be blocked by tetraethylammonium (50 microM). 3. N‐Methyl‐D‐aspartate (NMDA) and alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐proprionic acid (AMPA) failed to induce a response in neurones studies. 4. The spider venoms argiopine and argiopinine III (50‐500 nM) selectively inhibited quisqualate‐induced potassium current, but had no influence on glutamate‐, ibotenate‐ or quisqualate‐induced chloride and kainate‐induced potassium currents. Glutamate‐induced potassium current was partially inhibited by argiopine and argiopinine III. 5. The existence of several types of distinct glutamate receptors was confirmed in cross‐desensitization experiments, and a lack of interaction was observed between quisqualate and kainate. 6. Potassium currents induced both by quisqualate and kainate strongly depended on temperature and could be blocked by pertussis toxin. Intracellular injection of the calcium chelator, EGTA, did not affect quisqualate and kainate responses. 7. In neurones loaded with non‐hydrolysable GTP analogues, GTP‐gamma‐S (guanosine‐5'‐O‐(3‐thio)triphosphate) or GppNHp (5'‐guanylylimidodiphosphate), the potassium current was gradually induced in the absence of agonists. As this current progressed, the magnitude of the glutamate‐ or kainate‐evoked current transients became smaller and finally negligible. The GTP‐gamma‐S‐induced current was not inhibited by argiopine. 8. These data indicate that in the molluscan neurones studied there are at least three pharmacologically distinct glutamate receptors: (1) a receptor of quisqualate‐ibotenate type which directly controls chloride channel; (2) quisqualate and (3) kainate receptors which control in calcium‐independent manner the common potassium channel by activation of GTP‐binding protein.
Differential control of the inspiratory intercostal muscles during airway occlusion in the dog.
Authors: De Troyer A
Published: December 2014

1. The effect of airway occlusion on the electrical activity of the three groups of inspiratory intercostal muscles (external intercostal, levator costae, parasternal intercostal) situated in the cranial portion of the rib‐cage has been studied in thirty anaesthetized, spontaneously breathing dogs. 2. The three muscles were active during normal inspiration, and their activity was prolonged similarly during airway occlusion. However, a comparison of activity during occluded and unoccluded inspirations indicated that airway occlusion caused a facilitation of external intercostal and levator costae activities but an inhibition of parasternal intercostal activity. 3. The facilitation of external intercostal and levator costae activities was markedly reduced after section of the phrenic nerves and completely suppressed after section of the appropriate thoracic dorsal roots. 4. The inhibition of parasternal intercostal activity was not affected by section of the phrenic nerves or by section of the thoracic dorsal roots. This phenomenon, however, was abolished after bilateral cervical vagotomy. 5. Activation of the external intercostals and levator costae during inspiratory efforts are thus highly dependent on segmental reflexes arising in these muscles. In contrast, activation of the parasternal intercostals resembles that of the diaphragm in the sense that it depends primarily on the central respiratory drive.
Effects of vasoactive agonists on the membrane potential of cultured bovine aortic and guinea‐pig coronary endothelium.
Authors: Mehrke G , Pohl U , Daut J
Published: December 2014

1. The effects of bradykinin, ATP, adenosine, histamine and thrombin on the membrane potential of confluent monolayers of cultured bovine aortic endothelial cells (BAECs) and guinea‐pig coronary endothelial cells (GCECs) were studied at 37 degrees C using the whole‐cell mode of the patch‐clamp technique. 2. The amplitude histogram of the resting potentials of BAEC monolayers showed a bimodal distribution with one peak around ‐25 mV and another peak around ‐85 mV. Transitions from one potential level to the other were observed. The bistable membrane potential can be explained by an N‐shaped current‐voltage relation of the endothelial cell membrane. 3. When BAECs with a low resting potential (‐10 to ‐30 mV) were superfused with maximally effective concentrations of ATP (2‐10 microM) an initial hyperpolarization of ‐80 to ‐90 mV was observed which decayed to a plateau of about ‐60 mV within 1 min. When ATP was removed after 2‐3 min the membrane potential returned to control level within 1 min. This was followed by a second hyperpolarization of 10‐20 mV, which decayed within 15 min. 4. In the absence of extracellular calcium, ATP produced only a brief transient hyperpolarization in aortic endothelium. The plateau and the secondary hyperpolarization were abolished. These findings are consistent with the idea that the changes in membrane potential reflect changes in intracellular free Ca2+ and that the initial peak is due to release of Ca2+ from intracellular stores, whereas the plateau and the secondary hyperpolarization depend on transmembrane Ca2+ influx. 5. Bradykinin evoked potential changes similar to ATP in BAECs, except that the secondary hyperpolarization during wash‐out was absent. When the membrane potential was more negative than ‐80 mV, ATP and bradykinin induced only a small initial hyperpolarization followed by a depolarization of up to 20 mV. 6. In aortic endothelium, ADP (10 microM) evoked a much smaller response than ATP. Adenosine (10 microM), thrombin (2 units/ml), acetylcholine (10 microM) and histamine (10 microM) had only a very small effect on the membrane potential, if any. 7. The amplitude histogram of the membrane potential of GCECs showed only one peak around ‐35 mV. In coronary endothelium, application of bradykinin, ATP, histamine, thrombin, acetylcholine and adenosine all evoked a transient hyperpolarization of 10‐40 mV lasting 1 min or less, which then turned into a depolarization. 8. The K+ channel openers cromakalim (BRL 34915) and lemakalim (BRL 38227) did not affect the membrane potential of GCECs or BAECs.(ABSTRACT TRUNCATED AT 400 WORDS)
Development of calcium current subtypes in isolated rat hippocampal pyramidal cells.
Authors: Thompson S M , Wong R K
Published: December 2014

1. Patch‐clamp techniques were used to record from acutely dissociated rat hippocampal pyramidal cells of different postnatal ages to study the development, kinetics of activation and inactivation, and pharmacology of various components of whole‐cell calcium current. 2. In both adult and immature pyramidal cells, the threshold of activation for Ca2+ current from the holding potential of ‐50 mV was about ‐35 mV. The current was non‐inactivating near threshold, and slowly inactivating with stronger depolarizations. 3. In adult pyramidal cells, hyperpolarizing pre‐pulses (‐85 mV, 3 s) increased the peak amplitude of current, but had little effect on the amplitude of sustained current or on the threshold. In immature cells, hyperpolarizing pre‐pulses (‐85 mV, 3 s) revealed an additional component of Ca2+ current that had a threshold for activation around ‐60 mV, and inactivated rapidly and completely at potentials between ‐60 and ‐35 mV. This low‐threshold Ca2+ current was found in all cells less than 12 days of age, and in no cells older than 29 days of age. 4. No difference was observed between the Ca2+ currents elicited from CA3 or CA1 pyramidal cells. 5. The time course of decay for inactivating Ca2+ currents in adult cells at ‐20 mV was well fit with a single exponential of roughly 120 ms time constant. In immature cells, the addition of a second, faster time constant (roughly 25 ms) was required to describe the decay of the inactivating current adequately. The persistent Ca2+ current elicited from the holding potential of ‐50 mV decayed with a time constant of roughly 750 ms. The rate of inactivation for all Ca2+ current components was faster with stronger depolarizations. Inactivating Ca2+ currents contributed a significantly larger percentage of the total Ca2+ current in immature than adult cells. 6. Steady‐state inactivation of the low‐threshold Ca2+ current in immature cells was described by the Boltzmann equation with half maximal inactivation at ‐76 mV and a slope factor of 6.8. Recovery from inactivation was exponential, with a time constant of 820 ms (at ‐85 mV). Steady‐state inactivation of the high‐threshold inactivating Ca2+ current in adult cells was described by the Boltzmann equation with half maximal inactivation at ‐78 mV and a slope factor of 9.9. 7. The low‐threshold Ca2+ current in immature cells was blocked in a reversible and dose‐dependent manner by amiloride (100‐250 microM). Amiloride had no effect on high‐threshold Ca2+ currents.(ABSTRACT TRUNCATED AT 400 WORDS)
Time‐dependent changes in Ca2+ sensitivity during phasic contraction of canine antral smooth muscle.
Authors: Ozaki H , Gerthoffer W T , Publicover N G , Fusetani N , Sanders K M
Published: December 2014

1. Relationships between cytosolic Ca2+ concentration ([Ca2+]cyt), myosin light chain (MLC) phosphorylation and muscle tension were examined in circular smooth muscle of canine gastric antrum. 2. Electrical slow waves induced a transient increase in [Ca2+]cyt and muscle tension. [Ca2+]cyt increased before the initiation of contraction and reached a maximum before the peak of the phasic contractions. Following the first Ca2+ transient, a second rise in [Ca2+]cyt was often observed. The second Ca2+ transient was of similar magnitude to the first, but only in some cases was this increase in [Ca2+]cyt associated with a second phase of contraction. Relaxation occurred more rapidly than the restoration of resting levels of [Ca2+]cyt. 3. Acetylcholine (ACh; 3 x 10(‐7) M) increased the amplitude of Ca2+ transients, caused MLC phosphorylation and increased the force of contraction. The decay of contraction and MLC dephosphorylation preceded that of [Ca2+]cyt. 4. Increasing external K+ (to 25‐40 mM) caused a sustained increase in [Ca2+]cyt, but little change in resting tension. This suggests that the Ca2+ sensitivity decreased as [Ca2+]cyt increased. Increasing K+ to 59.5 mM further increased the level of [Ca2+]cyt, induced MLC phosphorylation and caused a transient contraction. When normal levels of K+ were restored, the rates of MLC dephosphorylation and relaxation exceeded the rate of decay in [Ca2+]cyt. 5. Removal of external Ca2+ in depolarized muscles decreased [Ca2+]cyt below the resting level without affecting resting tension. Readmission of Ca2+ to depolarized muscles caused force to develop at [Ca2+]cyt levels below the original resting level, suggesting that Ca2+ sensitivity was increased when the resting level of [Ca2+]cyt was decreased. 6. The phosphatase inhibitor, calyculin‐A (10(‐6) M), induced tonic contraction and MLC phosphorylation without an increase in [Ca2+]cyt. During these contractures, electrical activity caused transient increases in [Ca2+]cyt and phasic contractions which were superimposed upon the Ca(2+)‐independent contracture. In the presence of calyculin‐A, relaxation occurred in two phases. The initial, rapid phase of relaxation was not significantly affected by calyculin‐A, but the slow phase was significantly decreased. 7. These results suggest that the relationship between [Ca2+]cyt, MLC phosphorylation and contraction changes as a function of [Ca2+]cyt in canine antral muscles. This may be due to a Ca(2+)‐and time‐dependent phosphatase that regulates the level of myosin phosphorylation.
Evidence for a contribution of the motor cortex to the long‐latency stretch reflex of the human thumb.
Authors: Capaday C , Forget R , Fraser R , Lamarre Y
Published: December 2014

1. In normal subjects, transcranial magnetic stimulation of the hand region of the motor cortex evokes motor responses only in contralateral hand muscles at a latency of about 19‐24 ms. In contrast, stimulation of the motor cortex of three mirror movement subjects evoked, nearly simultaneously, motor responses in hand muscles on both sides of the body at latencies similar to those of normal subjects. In these subjects no other neuroanatomical pathways appear to be abnormally directed across the mid‐line. Thus, their mirror movements are probably due to a projection of the corticospinal tract to homologous motoneurone pools on each side of the body. 2. We reasoned that if the motor cortex contributes to the generation of long‐latency stretch reflex responses then in these mirror movement subjects stretching a muscle on one side of the body should produce long‐latency reflex responses in the ipsilateral and the homologous contralateral muscle. 3. To test this idea experiments were done on normal human subjects and on the subjects with mirror movements. The electromyographic (EMG) activity of the flexor pollicis longus muscle (FPL) on each side of the body was recorded. Stretch of the distal phalanx of the thumb of one hand produced a series of distinct reflex EMG responses in the ipsilateral FPL. The earliest response, when present, began at 25 ms (S.D. = 3.5 ms) and was followed by responses at 40 (S.D. = 3.9 ms) and 56 ms (S.D. = 4.3 ms). There was no difference, either in timing or intensity, between the ipsilateral FPL EMG responses of normal subjects and those of the mirror movement subjects. 4. No response of any kind was observed in the contralateral (unstretched) FPL of normal subjects. In contrast, we observed in all three mirror movement subjects EMG responses in the contralateral (unstretched) FPL beginning at 45‐50 ms. The latency of this response is considerably shorter than the fastest voluntary kinaesthetic reaction time, which was on average 130 ms (S.D. = 11 ms). The contralateral long‐latency EMG response observed in the mirror movement subjects was on average 30% (range 5‐60%) of that on the ipsilateral side. No short‐latency response (25 ms) was ever observed in the contralateral FPL of these subjects. 5. These observations are quite consistent with the idea that the long‐latency stretch reflex responses of hand and finger muscles are produced, at least in part, by the motor cortex.
Heat production in chemically skinned smooth muscle of guinea‐pig taenia coli.
Authors: Lönnbro P , Hellstrand P
Published: December 2014

1. The rate of heat production of chemically skinned guinea‐pig taenia coli smooth muscle at 25 degrees C was measured using microcalorimetric techniques. 2. Muscle strips were mounted isometrically and incubated in solutions containing MgATP (3.2 mM) and phosphocreatine (PCr, 12 mM), pH 6.9. Activation was obtained by the injection of Ca2+ into the sample compartment of the calorimeter. 3. The heat production rate of the resting preparation (pCa 9) was 0.40 +/‐ 0.03 mW g‐1 wet weight (n = 23). During maximal activation (pCa 4.8) the heat rate increased to 1.12 +/‐ 0.07 mW g‐1 (mean +/‐ S.E.M., n = 15). With stepwise increase in [Ca2+] from pCa 9 to 4.8 the energetic cost of force maintenance tended to increase at higher [Ca2+]. 4. After activation by Ca2+, the heat production rate reached its maximum while force was still increasing. 5. Changing ionic strength from 90 to 150 mM had no effect on either basal or activated heat rate. Oligomycin, amphotericin B and the adenylate kinase inhibitor Ap5A had no effect on the basal heat rate. 6. Exchanging ATP in the incubation medium for inosine triphosphate (ITP) reduced the force and heat production after injection of Ca2+. The basal heat production was not lowered when ATP was exchanged for ITP. 7. The observed enthalpy change for PCr splitting at 25 degrees C (pH 6.9, ionic strength 90 mM) was ‐28 +/‐ 3 kJ mol‐1 (mean +/‐ S.E.M., n = 9). After correction for the phosphate equilibrium, buffer reactions, and Mg2+ binding to PCr and HPO42‐, the net enthalpy change is calculated to be ‐39 +/‐ 3 kJ mol‐1. 8. Heat production in the skinned smooth muscle consists of one basal component present in relaxed muscle, and one component associated with contraction. The nature of the basal heat production is unclear but does not seem to involve turnover of phosphate on the myosin light chains. The increase in the energetic tension cost with increasing activation by Ca2+ has implications for the understanding of the contractile mechanism in smooth muscle.
Sodium‐calcium exchange in cultured bovine pulmonary artery endothelial cells.
Authors: Sage S O , van Breemen C , Cannell M B
Published: December 2014

1. Intracellular free calcium ([Ca2+]i) was measured in cultured bovine pulmonary artery endothelial cell monolayers loaded with the fluorescent calcium indicator Fura‐2. 2. Resting [Ca2+]i was 112 +/‐ 10 nM. Application of ouabain (20 microM) was without effect on [Ca2+]i for periods of up to 1 h. Monensin (10 microM) resting [Ca2+]i to 145 +/‐ 32 nM over approximately 2 min. In the presence of ouabain (20 microM), 10 microM‐monensin increased [Ca2+]i to 146 +/‐ 15 nM. 3. Removal of extracellular sodium was without effect in resting cells or cells exposed to ouabain alone. However, in the presence of monensin, replacement of extracellular Na+ with Li+ resulted in a prompt increase in [Ca2+]i to a peak of 280 +/‐ 37 nM, which then returned towards resting levels. When Na+ was removed in the presence of both ouabain and monensin, [Ca2+]i reached a peak of 585 +/‐ 53 nM. 4. When extracellular Na+ was replaced with K+, to achieve simultaneous Na+ removal and depolarization, [Ca2+]i reached a peak of 568 +/‐ 63 nM, compared with a peak of 462 +/‐ 38 nM when Li+ was used as a Na+ substitute in paired experiments. The transient increase in [Ca2+]i evoked by sodium removal peaked earlier when K+ was used as the sodium substitute, showing that depolarization increased the rate of calcium influx into the cell when sodium was removed from the bathing medium. 5. Removal of extracellular K+ had no effect on the low‐Na(+)‐evoked increase in [Ca2+]i. 6. Returning extracellular Na+ during the increase in [Ca2+]i resulting from Na+ removal increased the rate of return of [Ca2+]i towards basal levels. In the absence of Na+, [Ca2+]i took 41 +/‐ 5 s to decline from 400 to 200 nM, and this was reduced to 26 +/‐ 6 s (n = 4, S.E.M.) when Na+ was returned to the bathing solution. 7. These results indicate endothelial cells possess a voltage‐dependent Na(+) ‐Ca2+ exchange mechanism in the surface membrane. However, this mechanism does not appear to be of primary importance in the maintenance of resting [Ca2+]i since cells were able to restore a low [Ca2+]i in the absence of extracellular Na+. The evidence for the existence of a Na(+) ‐Ca2+ exchanger in the surface membrane of endothelial cells and the possibility that this mechanism may contribute to calcium entry and/or extrusion during agonist‐evoked responses is discussed.
ATP‐induced Ca2+ release and Cl‐ current in cultured smooth muscle cells from pig aorta.
Authors: Droogmans G , Callewaert G , Declerck I , Casteels R
Published: December 2014

1. The effect of exogenous ATP on transmembrane currents and on the cytoplasmic Ca2+ has been investigated in single cultured smooth muscle cells of pig aorta. 2. ATP applied to cells held at a potential of ‐50 mV evoked a transient inward current and a transient rise in [Ca2+]i. At a potential of +20 mV the ATP‐induced increase in [Ca2+]i was accompanied by an outward current. 3. At a potential of ‐50 mV, ATP evoked in Ca(2+)‐free solution an inward current which was similar to that in the presence of external Ca2+. A second application of ATP in Ca(2+)‐free solution induced a much smaller current. 4. ATP induced in Ca(2+)‐free solution a pronounced transient stimulation of the 45Ca2+ efflux from confluent smooth muscle monolayers. 5. The I‐V curve of the ATP‐activated current has a reversal potential close to 0 mV. A reduction of external Cl‐ shifts this reversal potential in accordance with the change of the Cl‐ equilibrium potential. 6. It is concluded that ATP causes a release of calcium from intracellular stores. The ensuing increase of [Ca2+]i activates a Cl‐ current, which can depolarize the cell membrane and thereby promote a voltage‐gated Ca2+ entry.
Excitation by geniculocortical synapses is not ‘vetoed’ at the level of dendritic spines in cat visual cortex.
Authors: Dehay C , Douglas R J , Martin K A , Nelson C
Published: December 2014

1. We used anatomical methods to examine whether the geniculocortical afferent input to dendritic spines could be gated or ‘vetoed’ by an inhibitory input to the same spine. 2. Physiologically identified X‐ and Y‐type afferents were injected intra‐axonally with horseradish peroxidase (HRP), processed, and drawn under the light microscope. Selected regions of the terminal arbors were then serially sectioned for examination under the electron microscope. 3. Three‐dimensional reconstructions of thirty‐nine HRP‐filled terminal boutons forming fifty asymmetric (type 1) synapses showed that thirty‐one synapses were on the heads of dendritic spines. Only two of thirty‐one spine heads received an additional symmetric (type 2) synapse, which is presumed to be inhibitory. 4. Examination of twenty‐three boutons from two clutch cells (a GABA (gamma‐aminobutyric acid)‐ergic smooth cell) that form symmetric (type 2) synapses on spines indicated that their preferred location was opposite the asymmetric synapse on the head of the spine. Synaptic input to the necks of spines appears rare. 5. We conclude that most of the excitation provided by the geniculocortical afferent input to the heads of spines cannot be gated or vetoed by inhibition at the level of the spine.
Inhibition of tubuloglomerular feedback by the D1 agonist fenoldopam in chronically salt‐loaded rats.
Authors: Häberle D A , Königbauer B
Published: December 2014

1. Chronic dietary NaCl loading in rats is paralleled by an increase of the dopamine concentration in the tubular fluid and humorally mediated inhibition of the tubuloglomerular feedback mechanism at the macula densa. Since these two phenomena are causally linked, the alterations in the tubuloglomerular feedback response by the luminal application of dopamine, the D1 agonist fenoldopam, the D2 agonist bromocriptine and the D1 and D2 antagonists SCH 23390 and metoclopramide were further investigated using the micropuncture technique. 2. Very similar, concentration‐dependent inhibition of the tubuloglomerular feedback response was observed for dopamine and fenoldopam. Half‐maximal inhibition was achieved at 10(‐11) M and the slope factors of the sigmoid concentration‐response curves were comparable. Bromocriptine was ineffective. 3. The inhibition of TGF by both agonists could be antagonized very similarly and concentration dependently by the D1 antagonist SCH 23390. At equimolar concentrations of 10(‐9) M the inhibition was reduced by approximately 50%. Raising the SCH 23390 concentration to 10(‐6) M completely abolished the TGF inhibition. In contrast, TGF inhibition by 10(‐9) M‐fenoldopam or dopamine was not significantly affected by an equimolar concentration of the D2 antagonist metoclopramide. Increasing metoclopramide concentration to 10(‐6) M attenuated tubuloglomerular feedback inhibition by approximately 55%. 4. It is concluded that the inhibition of tubuloglomerular feedback seen during chronic dietary salt loading can be ascribed to the binding of endogenous dopamine to luminal D1 receptors on the macula densa cells.
Parvalbumin content and Ca2+ and Mg2+ dissociation rates correlated with changes in relaxation rate of frog muscle fibres.
Authors: Hou T T , Johnson J D , Rall J A
Published: December 2014

1. Experiments were done to test the hypothesis that parvalbumin (PA) promotes relaxation in frog skeletal muscle. Single fibres and purified PA from Rana temporaria skeletal muscle were used to determine the relationship between PA concentration ( [PA] ), Ca2+ and Mg2+ dissociation rates from PA and changes in rate of relaxation as a function of tetanus duration at 0 degrees C. 2. Total [PA] in fibres from tibialis anterior muscles is 0.76 +/‐ 0.20 mmol PA l‐1 myoplasmic water (mean +/‐ S.D., n = 25) with 65% PA IVa and 35% PA IVb, where PA IVa and PA IVb are PA isoforms. 3. Relaxation rate from an isometric tetanus shows progressively as a function of tetanus duration with an exponential time course and a rate constant of 1.18 +/‐ 0.35 s‐1 (n = 17). Time course of recovery of relaxation rate after a prolonged tetanus is exponential with a rate constant of 0.12 +/‐ 0.02 s‐1 (n = 14). 4. The extent of recovery of relaxation rate after a prolonged tetanus was correlated with total [PA] in fibres (correlation coefficient (r) = 0.80, n = 7; P less than 0.05). 5. Dissociation rate constants for Mg2+ and Ca2+ from purified PA are 0.93 +/‐ 0.02 s‐1 (n = 5) and 0.19 +/‐ 0.01 s‐1 (n = 5), respectively. Dissociation rate constants were not significantly different for PA isoforms IVa and IVb. These rate constants are similar to the rate constants determined for the time courses of slowing and recovery of relaxation rate, respectively. 6. Results suggest that the time courses of slowing and recovery of relaxation rate may be controlled, to a large extent, by Mg2+ and Ca2+ dissociation from PA, respectively. This evidence supports a role for PA in facilitating relaxation during a tetanus in frog skeletal muscle at 0 degrees C.
Acetazolamide on the ventral medulla of the cat increases phrenic output and delays the ventilatory response to CO2.
Authors: Coates E L , Li A H , Nattie E E
Published: December 2014

1. Acetazolamide (0.1 mM) applied to the surface of the rostral ventrolateral medulla or microinjected beneath the medullary surface in chloralose‐urethane‐anaesthetized, vagotomized, carotid‐denervated, paralysed, servo‐ventilated cats produced a long‐lasting increase in integrated phrenic nerve activity. 2. Extracellular pH measured beneath the rostral ventrolateral medulla exhibited a long‐lasting decrease after surface acetazolamide but was not a good predictor, in each individual animal, of changes in phrenic activity. 3. Medullary carbonic anhydrase inhibition reduced the slope and the half‐time of the phrenic response to rapid step CO2 increases. Conversely, acetazolamide did not affect the phrenic response to steady‐state CO2 increases. 4. These data indicate that localized inhibition of medullary carbonic anhydrase causes a centrally mediated increase in ventilation that we attribute to medullary tissue hypercapnia and acidosis. In addition, these data indicate that medullary carbonic anhydrase may play a role in central CO2 chemotransduction.
Activation of inositol trisphosphate‐sensitive Ca2+ channels of sarcoplasmic reticulum from frog skeletal muscle.
Authors: Suárez‐Isla B A , Alcayaga C , Marengo J J , Bull R
Published: December 2014

1. The modulation by Ca2+ of the activation by inositol 1,4,5‐trisphosphate (IP3) of Ca2+ channels present in native sarcoplasmic reticulum membranes from frog skeletal muscle was studied after channel incorporation into planar phospholipid bilayers in the presence of Ca2+ or Ba2+ as current carrier species. 2. Channel activity expressed as fractional open time (Po) was low (less than or equal to 0.15) in the presence of varying free Ca2+ concentrations bathing the myoplasmic face of the channel (cis side), and did not increase significantly between 0.01 and 30 microM‐Ca2+. 3. Channel activation mediated by IP3 could be elicited from free Ca2+ levels similar to those of resting skeletal muscle (about 0.1 microM) and was found to be strongly regulated by the free Ca2+ concentration present at the myoplasmic moiety of the channel. 4. Channel activation by 10 microM‐IP3 depended on the Ca2+ concentration on the cis side. Po reached a maximum between pCa 7.0 and 6.0, but decreased at higher concentrations of free Ca2+. Thus, Ca2+ exerted a modulatory influence on IP3‐mediated activation in a concentration range where the channel was insensitive to Ca2+. 5. The results indicate that Ca2+ ions act as modulators of IP3 efficacy to open the channel. This could arise from an interaction of Ca2+ with the channel gating mechanism or with the agonist binding site.
Human peripheral spatial resolution for achromatic and chromatic stimuli: limits imposed by optical and retinal factors.
Authors: Anderson S J , Mullen K T , Hess R F
Published: December 2014

1. The aim of this study was to determine whether optical, receptoral or higher‐order neural properties limit spatial resolution (acuity) in human vision, especially in the peripheral regions of the visual field. 2. Both achromatic and chromatic stimuli were used, and measures were taken to ensure that the resolution estimates were not contaminated by the detection of spatial sampling artifacts. Spatial contrast sensitivity functions were measured at retinal locations from 0 to 55 deg along the naso‐temporal meridian for: (i) discriminating the direction of drift of luminance‐modulated (black‐white) sinusoidal stimuli drifting at 8 Hz (achromatic task); and (ii) for detecting isoluminant red‐green sinusoidal stimuli drifting at 0.4 Hz (chromatic task). Achromatic contrast sensitivity functions were also measured along the vertical meridian for eccentricities of 8 and 40 deg. Each achromatic function was extrapolated to a contrast sensitivity of one (100% contrast) to estimate achromatic acuity. Chromatic acuities were obtained by expressing chromatic contrast in terms of cone contrasts and using the same method of extrapolation. We compared the results with recent data on human optical properties and retinal anatomy. 3. Both achromatic and chromatic acuity decline with distance from the fovea, but at a faster rate than that dictated by the known optical and/or receptoral properties of the human eye. We conclude that, for stimuli of either achromatic or chromatic contrast, peripheral spatial resolution is limited by post‐receptoral mechanisms. Also, chromatic acuity declines more steeply than luminance acuity with eccentricity suggesting that there are additional post‐receptoral limitations on colour resolution in the periphery. 4. A clear naso‐temporal asymmetry is seen in the resolution whose dependence is qualitatively, but not quantitatively, similar to the Nyquist limits imposed by the asymmetric density of human retinal ganglion cells. We discuss the possibility that in peripheral vision (beyond the optic nerve head) the spacing of ganglion cells may pose a fundamental limit on the resolution of achromatic stimuli, but not chromatic stimuli.