bluuebunny/crossref_metadata_2025 huggingface dataset:
Ca2+ regulation of the contractile apparatus in canine gastric smooth muscle.
Authors: Ozaki H , Gerthoffer W T , Hori M , Karaki H , Sanders K M , Publicover N G
Published: December 2014

1. The relationships between cytosolic Ca2+ ([Ca2+]cyt; expressed as a fluorescence ratio at 400 nm and 500 nm using Indo‐1) and contractile force was examined in strips of circular smooth muscles of canine gastric antrum. Rhythmic increases in [Ca2+]cyt were observed and contractions were biphasic. 2. In most muscles (70%), the amplitude of the second phase of the Ca2+ transient was less than or equal to the first phase of the Ca2+ transient, but the second phase of the contraction was much smaller than the first phase, suggesting a decrease in Ca2+ sensitivity during the second contractile phase. In 30% of muscles, the amplitude of the second phase of the Ca2+ transient was 2‐ to 3‐fold greater than the first phase. In these muscles, the second phase of contraction was 10‐fold greater than the first phase of contraction. Thus, a non‐linear relationship between [Ca2+]cyt and force greatly amplifies force development when [Ca2+]cyt exceeds a threshold level. 3. Acetylcholine (ACh, 0.3‐1 microM) increased the amplitudes of Ca2+ transients and basal [Ca2+]cyt between phasic contractions. The increase in basal [Ca2+]cyt did not cause tone to develop. ACh increased the amplitude of Ca2+ transients 2‐ to 3‐fold and this was associated with a 15 to 20‐fold increase in the force of phasic contractions. Pentagastrin (0.5 nM) and cholecystokinin octapeptide (CCK, 40 nM) had similar effects on Ca2+ transients and phasic contractions. 4. Bay K 8644 (0.1 microM) and TEA (5 mM) also increased the amplitudes of Ca2+ transients by 2‐ to 3‐fold and phasic contractions by 15‐ to 30‐fold. There was no significant difference observed between the [Ca2+]cyt‐force relationships in the presence of agonists (i.e. ACh, pentagastrin and CCK) or when [Ca2+]cyt was increased by Bay K 8644 or TEA. These data suggest that agonist‐dependent increases in Ca2+ sensitivity may not significantly regulate the [Ca2+]cyt‐force relationship in antral muscles. 5. D600 (5 microM), added during stimulation with ACh (0.3 M), decreased [Ca2+]cyt and force without affecting the [Ca2+]cyt‐force relationship. 6. Mechanisms exist for agonist‐mediated enhancement of the Ca(2+)‐force relationship. In alpha‐toxin‐permeabilized antrum, ACh (10 microM) with GTP (100 microM) or GTP gamma S (100 microM) increased the Ca(2+)‐induced contraction at clamped levels of Ca2+. Phorbol 12,13‐dibutyrate (PDBu, 10 microM) also increased the contractile force at a given level of Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Involvement of intrahepatic innervation in caesium‐induced haemodynamic oscillations in the rat liver.
Authors: Hill C E , Myers J W , Pon D C
Published: December 2014

1. Cs+ was used to study the mechanisms involved in the induction of haemodynamic and metabolic oscillations in the isolated rat liver perfused by the portal vein. 2. Cs+ (2.25 mM) in K(+)‐free perfusate causes the appearance of periodic increases in portal pressure (3.87 +/‐ 0.6 mmHg, n = 24) and decreases in O2 uptake (111 +/‐ 26 microM) at a frequency of 0.013 +/‐ 0.002 Hz. A 19.8 +/‐ 1.2 min induction time occurs prior to the generation of periodicity. The oscillations are interspersed with low amplitude shoulders and peaks indicating multiple non‐phasic components. 3. Cs+ concentrations higher or lower than 2.25 mM decrease oscillation amplitude and render them aperiodic. No oscillations are observed with 0.5 or 12.5 mM Cs+. 4. The oscillations are reversibly blocked by 1 mM K+, 1 mM EGTA, 5 microM verapamil or 0.17 microM tetrodotoxin. One micromolar chlorpheniramine, 10 microM propranolol, 12 microM phentolamine or 35 microM atropine also maximally inhibit the Cs(+)‐induced vasoactivity. 5. The results show that the liver perfused by the portal vein has all of the components required to activate vascular synchrony including intrinsic neural input and responsive vasoactive cells.
The cutaneous vascular axon reflex in humans characterized by laser Doppler perfusion imaging.
Authors: Wårdell K , Naver H K , Nilsson G E , Wallin B G
Published: December 2014

1. Laser Doppler perfusion imaging was used to map the cutaneous vascular axon response induced by trains of electrical skin stimuli (1 ms, 2 Hz) on the dorsum of the hand, finger and foot in twenty‐four healthy subjects. Conduction anaesthesia was applied to nerves supplying the stimulated skin areas. Subtraction of images recorded before and after stimulation was used for data analysis of the intensity and area of the response. 2. The stimulation evoked a localized perfusion increase around the stimulating electrode which lasted approximately 30 min and increased in intensity and area with increasing stimulation strength to a maximum at 20 pulses and 20 mA. The intensity and area of the response was greater on the hand than on the foot. 3. Approximating the response area as a circle, the maximal perfusion increase in the hand extended 9 +/‐ 3 mm (mean +/‐ S.D.) outside the perimeter of the stimulating electrode. When stimulating within skin which had been subjected to surface anaesthesia, no response occurred, but when stimulating at the border of surface‐anaesthetized skin, the perfusion increase extended 2 +/‐ 1 mm (mean +/‐ S.D.) into anaesthetized skin. 4. The results show that the perfusion increase must have been due in part to impulse conduction to, and release of transmitters from, axon endings terminating in skin outside the contact area of the probe. It is concluded that the area of perfusion increase corresponds to the size of the receptive fields of afferent polymodal C fibres.
Electrical and integrative properties of rabbit sympathetic neurones re‐evaluated by patch clamping non‐dissociated cells.
Authors: Gola M , Niel J P
Published: December 2014

1. Voltage recordings were performed on non‐dissociated sympathetic neurones from rabbit coeliac ganglia using the whole‐cell configuration of the patch clamp technique. 2. Cells were classified depending on their firing pattern as silent cells (63%) producing either phasic (24%) or tonic (76%) spike discharge in response to depolarizing currents, and pacemaker cells (37%). 3. All the cells produced large overshooting spikes and prolonged postspike after‐hyperpolarization. The peak‐to‐peak spike amplitude was 113.8 +/‐ 1 mV. Spikes were shortened and the after‐hyperpolarization was suppressed when calcium channel blockers (Cd2+ and La3+) were added. 4. Silent cells have a resting potential of ‐58.8 +/‐ 1.5 mV. At potentials ranging from ‐50 to ‐90 mV, the input impedance was 490 +/‐ 27 M omega at 22‐24 degrees C and 426 +/‐ 47 M omega at 35‐36 degrees C. The time constant at voltages corresponding to the high input impedance region was 126 +/‐ 7 ms at 22‐24 degrees C and 86 +/‐ 7 ms at 35‐36 degrees C. 5. The firing frequency of the pacemaker cells was 3.2 +/‐ 0.5 Hz at 35‐36 degrees C in the presence of nicotinic blockers. Evidence is given that the firing did not result from cell injury but was induced by an intrinsic pacemaker mechanism. Input impedance of pacemaker neurones was 580 +/‐ 47 M omega at 22‐24 degrees C and 473 +/‐ 56 M omega at 35‐36 degrees C. 6. Most of the pacemaker cells (63%) were motoneurones, since they were antidromically fired by stimulating post‐ganglionic nerves. In addition, they received synaptic inputs from both preganglionic fibres (splanchnic nerves) and the periphery (postganglionic nerves). Long‐lasting depolarizations were induced in either silent or pacemaker cells by single shocks applied to pre‐ and postganglionic nerves. 7. Slowly rising voltage ramps revealed the presence of an N‐shaped current‐voltage relationship in voltage clamped pacemaker cells. The negative slope was located in a subthreshold voltage range, between ‐83.4 +/‐ 1.4 and ‐59.0 +/‐ 1.8 mV. It was induced by the activation of a low threshold persistent inward current. Although it was tiny (22 +/‐ 3 pA at its peak level) this current brought the null‐current voltage up to ‐41.0 +/‐ 1.4 mV, which resulted in continuous firing. 8. Due to the instability introduced by the N‐shaped I‐V relationship, pacemaker cells can display bistable behaviour characterized by hyperpolarizing responses.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of amiloride and ouabain on short‐chain fatty acid transport in guinea‐pig large intestine.
Authors: von Engelhardt W , Burmester M , Hansen K , Becker G , Rechkemmer G
Published: December 2014

1. Effects of H+ secreting mechanisms on unidirectional passage of the short‐chain fatty acids (SCFA) acetate, propionate and n‐butyrate across isolated guinea‐pig caecum, proximal and distal colon were studied under short‐circuit current conditions in Ussing chamber isotope flux experiments. 2. In the caecum and the proximal colon the serosal‐to‐mucosal fluxes (Jsm) were higher than the mucosal‐to‐serosal fluxes (Jms). Thus a net secretion of SCFA was present in the caecum and proximal colon. The higher Jsm appears to be coupled to the Na+ gradient established by the basolateral membrane Na(+)‐K(+)‐ATPase, whereas Jms is related to the operation of an apical membrane Na(+)‐H+ exchanger. Inhibition of Na(+)‐H+ exchange by amiloride (1 mM) added to the mucosal solution decreased Jms of SCFA in caecum and in proximal colon, but had no major effect in distal colon. 3. In distal colon Jms exceeds Jsm and thus a net absorption of SCFA was observed. Jms is Na+ independent and coupled to the activity of the apical membrane K(+)‐H(+)‐ATPase. Inhibition of the K(+)‐H(+)‐ATPase by addition of ouabain (0.1 mM) to the mucosal solution diminished Jms in the distal colon; in the caecum and proximal colon ouabain had no effect on Jms. 4. Neither amiloride nor ouabain caused major changes in Jsm in any of the large intestinal segments. 5. In conclusion, absorption of SCFA, e.g. Jms, in all large intestinal segments is related to the presence and activity of H+ secreting systems located in the apical membrane of colonocytes. In the caecum and proximal colon the predominant system appears to be Na(+)‐H+ exchange, and in the distal colon K(+)‐H(+)‐ATPase. Supply of H+ ions allows protonation of SCFA anions and subsequent permeation by non‐ionic diffusion across the apical membrane. These mechanisms account for 35, 40‐50 and 60‐80% of SCFA transport in the caecum, the proximal and the distal colon of guinea‐pig, respectively. The nature of the Na(+)‐dependent secretory pathway in the caecum and proximal colon remains to be determined.
Asynchronous increases in oxidative capacity and resistance to fatigue of electrostimulated muscles of rat and rabbit.
Authors: Simoneau J A , Kaufmann M , Pette D
Published: December 2014

1. The present study investigates to what extent increases in resistance to fatigue and aerobic oxidative capacity of energy metabolism are correlated in fast‐twitch tibialis anterior muscles of rat and rabbit subjected to chronic low‐frequency stimulation. 2. Changes in the aerobic oxidative capacity of the stimulated muscles were judged from increases in citrate synthase activity, representing the constant‐proportion enzyme group of the citric acid cycle. 3. Resistance to fatigue reached maximal values in both rat and rabbit tibialis anterior muscles after stimulation periods of 14 days, whereas citrate synthase activity continued to increase with longer stimulation periods. 4. Different time courses of the changes in resistance to fatigue and citrate synthase activity were observed not only with prolonged stimulation periods but also during the first week, when pronounced increases in resistance to fatigue were accompanied by only moderate elevations in citrate synthase activity. 5. The dissociation between the changes of the two parameters studied suggests that factors other than elevated aerobic oxidative capacity contribute to enhanced resistance to fatigue.
Spatial facilitation and depression within one motor nerve terminal of frogs.
Authors: Dudel J , Parnas I , Parnas H
Published: December 2014

1. Perfused macropatch electrodes were used to stimulate and simultaneously measure release from two sites on the same terminal of the frog cutaneous pectoris muscle. 2. It was found that release occurring at one site often affected release at an adjacent site 50 microns away, either enhancing it ('spatial facilitation') or depressing it ('spatial depression'). Spatial facilitation (or depression) was defined as the release produced by a test pulse at the second site (test electrode) when preceded by a pulse at the first site (prepulse electrode) divided by the release produced by the test pulse alone. 3. Spatial facilitation varied with the time interval between the prepulse and the test pulse. Peak spatial facilitation, which on the average was 2.14, occurred with an interval of 1‐3 ms. With longer intervals spatial facilitation decayed with a time constant between 3‐6 ms. When the time interval between the prepulse and the test pulse was zero (no delay), the release after the test pulse was always depressed. 4. When Ca2+ was omitted from the perfusate of the prepulse electrode, spatial facilitation was abolished. When a brief hyperpolarizing pulse followed the depolarizing prepulse with zero delay spatial facilitation was also abolished. 5. Electrotonic spread or Ca2+ diffusion within the axon terminal are excluded as coupling agents for spatial facilitation. It is suggested that the coupling agent may possibly be related to a hypothetical release‐promoting factor.
Small‐conductance Cl‐ channels in rabbit parietal cells activated by prostaglandin E2 and inhibited by GTP gamma S.
Authors: Sakai H , Takeguchi N
Published: December 2014

1. Small‐conductance, sub‐picosiemens (sub‐pS) Cl‐ channels in the basolateral membrane of non‐stimulated parietal cells in isolated rabbit gastric glands were studied by whole‐cell patch‐clamp and noise analysis techniques. 2. Voltage‐independent whole‐cell Cl‐ currents were recorded from parietal cells equilibrated with Cl(‐)‐containing solutions. Intracellular application of guanosine‐5'‐O‐(3‐thiotriphosphate) (GTP gamma S, 5‐200 microM) slowly decreased the whole‐cell Cl‐ current, and its steady‐state effect was observed about 6 min after the start of the dialysis. The half‐maximal inhibitory concentration of GTP gamma S was about 60 microM. 3. The single Cl‐ channel conductance was estimated to be 0.37 pS from the variance noise analysis during the GTP gamma S‐induced inhibitory process of the whole‐cell Cl‐ current. It is in agreement with the value obtained by a method of power spectrum analysis (0.47 pS). 4. The whole‐cell Cl‐ current was increased by prostaglandin E2 (10 microM). The increased Cl‐ current was reduced by the subsequent application of GTP gamma S (50 microM), whereas the GTP gamma S (50 microM)‐induced inhibition of the Cl‐ current was not reversed by the subsequent application of prostaglandin E2 (10 microM). 5. The combined intracellular application of GTP gamma S (50 microM) and GDP beta S (500 microM) markedly reduced the inhibitory effect of GTP gamma S, indicating that a GTP‐binding protein is involved in the regulation of the Cl‐ channel. 6. Treatment of parietal cells with pertussis toxin (PTX, 500 ng/ml) for 90‐140 min did not affect the GTP gamma S‐induced inhibition of the whole‐cell Cl‐ current. 7. Intracellular application of cyclic AMP‐dependent protein kinase inhibitor peptide (100 micrograms/ml) or 1,2‐bis(O‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA) (5 mM, pCa 8) did not affect the GTP gamma S‐induced inhibition of the whole‐cell Cl‐ current. 8. The present study has suggested that the opening of the sub‐pS Cl‐ channel is modulated negatively by a PTX‐insensitive GTP‐binding protein and positively by prostaglandin E2.
Ca(2+)‐dependent heat production by rat skeletal muscle in hypertonic media depends on Na(+)‐Cl‐ co‐transport stimulation.
Authors: Chinet A
Published: December 2014

1. The rate of energy dissipation (E) in isolated, superfused soleus muscles from young rats was continuously measured under normosmotic and 100‐mosM hyperosmotic conditions. The substantial increase of E with respect to basal level in hyperosmolarity (excess E), which is entirely dependent on the presence of extracellular sodium, was largely prevented or inhibited by bumetanide, a potent inhibitor of Na(+)‐Cl‐ co‐transport system, or by the removal of chloride from the superfusate (isethionate substitution). Bumetanide or the removal of chloride also acutely decreased basal E, by about 7%. 2. Bumetanide almost entirely suppressed the major, Ca(2+)‐dependent part of excess E in hyperosmolarity, as well as the concomitant increase of 45Ca2+ efflux and small increase in resting muscle tension; in contrast, the part of excess E associated with stimulation of Na(+)‐H+ exchange in hyperosmolarity was left unmodified. 3. Reduction of 22Na+ influx by bumetanide was more marked in hyperosmolarity than under control conditions, although stimulation of total 22Na+ influx by a 100‐mosM stress was not statistically significant. Inhibition of Ca2+ release into the sarcoplasm using dantrolene sodium did not prevent the stimulation of bumetanide‐sensitive 22Na+ influx, but rather increased it about fourfold. 4. It is concluded that the largest part of excess E in hyperosmolarity, which is Ca(2+)‐dependent energy expenditure, is suppressed when steady‐state stimulation of a Na(+)‐Cl‐ co‐transport system is inhibited either directly by bumetanide or the removal of extracellular chloride, or indirectly by the blocking of active Na(+)‐K+ transport. How the stimulation of Na(+)‐Cl‐ co‐transport, by as little as 1 nmol s‐1 (g wet muscle weight)‐1 during a 100‐mosM stress, enhances Ca(2+)‐dependent heat by as much as 2.5 mW (g wet muscle weight)‐1 remains to be clarified.
Interconversion between distinct gating pathways of the high threshold calcium channel in rat ventricular myocytes.
Authors: Richard S , Charnet P , Nerbonne J M
Published: December 2014

1. High‐voltage‐activated Ca2+ current (ICa) waveforms in adult rat ventricular myocytes comprise two components, referred to here as ICa(fc) and ICa(sc) to denote the fast and slow components, respectively, of ICa decay. At all test potentials, the two time constants of ICa decay, tau fc and tau sc, differ by approximately an order of magnitude. Neither tau fc nor tau sc varies appreciably with test potential, however, suggesting that current inactivation is not markedly voltage dependent. 2. Current activation at all test potentials follows a sigmoidal time course and is best described by a power function with n = 4. Deactivation of the currents, examined following variable length depolarizations to various test potentials, however, follows a single exponential time course. In addition, the kinetics of activation and deactivation of ICa(fc) and ICa(sc) are indistinguishable. 3. Although both begin to activate at approximately ‐30 mV, the voltage dependences of ICa(fc) and ICa(sc) are distinct: ICa(fc) peaks at ‐10 mV and ICa(sc) peaks at +10 mV. 4. The relative amplitudes of ICa(fc) and ICa(sc) vary with the holding potential from which the currents are evoked and with the frequency of current activation: hyperpolarized holding potentials and low stimulation frequencies reveal preferential activation of ICa(fc), whereas depolarized holding potentials and high stimulation frequencies potentiate ICa(sc). In addition, the observed voltage‐ and frequency‐dependent changes in ICa(fc) and ICa(sc) amplitudes are reciprocal. 5. The apparent voltage dependences of steady‐state inactivation of ICa(fc) and ICa(sc) are also distinct. ICa(fc) is reduced to approximately 50% of its maximal amplitude at ‐45 mV, whereas ICa(sc) is approximately 50% inactivated at ‐30 mV. 6. Recovery of ICa(peak) from steady‐state inactivation follows a complex time course. Following inactivation at ‐10 mV, ICa(peak) recovers at ‐90 mV to its maximal value over a biexponential time course; ICa(peak) then decreases over the next several seconds to a steady‐state level. 7. The time course of recovery from steady‐state inactivation of ICa(fc) at ‐90 mV is best described by the sum of two exponentials; the two time constants of recovery differ by approximately a factor of 25. ICa(sc), in contrast, recovers rapidly and over a single exponential time course to its maximal value. When the recovery time at ‐90 mV is increased, however, ICa(sc) amplitude decreases slowly and over a single exponential time course to a steady‐state level.(ABSTRACT TRUNCATED AT 400 WORDS)
Cyclic AMP mediates inhibition of the Na(+)‐K+ electrogenic pump by serotonin in tactile sensory neurones of the leech.
Authors: Catarsi S , Scuri R , Brunelli M
Published: December 2014

1. Serotonin (5‐HT) reduced the after‐hyperpolarization (AHP) amplitude in tactile sensory neurones (T) but not in pressor (P) or nociceptive (N) cells of the leech. 2. Adenylate cyclase activators, phosphodiesterase inhibitors and membrane permeant analogues of cyclic adenosine monophosphate (cyclic AMP) mimicked the effect of 5‐HT in reducing the AHP amplitude in T neurones. 3. Ionophoretic injection of cyclic AMP in T cells reduced the AHP amplitude, while cyclic guanosine monophosphate (cyclic GMP) or adenosine‐5'‐monophosphate (AMP) were without effect. 4. Inhibition of adenylate cyclase by the drug RMI 12330A (also known as MDL 12330A) suggested that 5‐HT reduced the AHP amplitude through cyclic AMP. 5. 8‐Bromoadenosine‐3'‐5'‐cyclic monophosphate (8‐Br‐cyclic AMP) was still able to reduce the AHP amplitude after blocking the Ca(2+)‐activated K+ conductance with CdCl2 and converted the normal hyperpolarization which follows the intracellular injection of Na+ into a depolarization. In addition, the cyclic AMP analogue slowed down and reduced the repolarization usually induced by CsCl after perfusion with K(+)‐free solution. It is proposed that, in T sensory neurones, cyclic AMP mediates the inhibition of the Na(+)‐K+ electrogenic pump induced by 5‐HT application.
Effects of memory from vagal feedback on short‐term potentiation of ventilation in conscious dogs.
Authors: Xi L , Smith C A , Saupe K W , Dempsey J A
Published: December 2014

1. We assessed short‐term potentiation of ventilation in response to brief systemic normocapnic hypoxaemia in conscious dogs. Four recumbent dogs were exposed to Pa, O2 35‐55 mmHg with Pa, CO2 maintained normocapnic for forty to fifty seconds and then abruptly returned to normoxia. Minute ventilation (VI) increased 4‐ to 5‐fold during hypoxia due to both increased tidal volume (VT) and frequency (f). Several trials of hypoxic exposure with normoxic restoration were conducted with animals intact and following bilateral cold blockade of the cervical vagus nerves sufficient to block completely the Hering‐Breuer reflex. 2. In the vagally intact dog, when normoxia was restored immediately following normocapnic hypoxia (PET, O2 = 40 Torr), expiratory time (TE) was prolonged to 190 +/‐ 68% of control (mean +/‐ S.E.M., range 53‐350%) on the second or third breath and then returned slowly to control values on subsequent breaths. The prolongation of TE following removal of the hypoxic stimulus was positively correlated with the magnitude of the peak VT reached during hypoxic exposure. However, VT and VI remained significantly greater than control over a twenty second or four‐breath period following hypoxia. 3. In the vagally blocked dog, no prolongation of TE was observed following isocapnic hypoxia; nor was TE following hypoxia correlated with the magnitude of the VT during hypoxia. The time constants of decay of VI, VT and f back to control, following hypoxia averaged 16, 19 and 9 s, respectively. 4. We conclude that short‐term potentiation of ventilatory output following peripheral chemoreceptor hypoxic stimulation does exist in the awake dog, but the stimulatory after‐effect is masked and TE is prolonged by a ‘memory’ of inhibitory vagal feedback. The magnitude of this inhibitory after‐effect on TE prolongation increases in proportion to the increase in tidal volume achieved during the hypoxaemia. 5. This inhibitory effect of vagal memory may contribute to instability of breathing pattern and apnoea following transient disturbances in ventilatory output.
Guanine nucleotide binding proteins mediate D2 dopamine receptor activation of a potassium channel in rat lactotrophs.
Authors: Einhorn L C , Oxford G S
Published: December 2014

1. The involvement of guanine nucleotide binding proteins in the coupling of D2 dopamine (DA) receptors to single potassium channels was examined in rat pituitary lactotrophs. 2. Lactotrophs were unambiguously identified by the reverse haemolytic plaque assay (RHPA) and membrane potentials, whole‐cell and single channel currents recorded using patch electrode methods. 3. DA or the D2 selective agonist, quinpirole, induced the opening of single K+ channels in cell‐attached patches underlying robust hyperpolarizations of membrane potential in single cells. 4. Both whole‐cell and single channel responses were independent of Ca2+ or cAMP concentrations. 5. Pertussis toxin (PTX) pretreatment (50‐250 ng/ml, 6‐12 h) blocked the action of DA on lactotroph membrane potential and uncoupled D2 receptors from single K+ channels in cell‐attached patches. 6. Internal dialysis with GDP beta S (guanosine 5'‐O‐(2‐thiodiphosphate) greatly reduced whole‐cell responses to DA in a dose‐dependent manner. 7. Internal dialysis of lactotrophs with GTP gamma S (guanosine 5'‐O‐(3‐thiotriphosphate) potentiated DA responses in a dose‐dependent manner while rendering the responses irreversible at higher doses. 8. DA (100 nM) or quinpirole (10 microM) activated K+ channels in excised outside‐out membrane patches that were identical to those identified in cell‐attached patches in terms of conductance and gating kinetics. 9. It is proposed that D2 receptors are coupled to non‐voltage‐dependent K+ channels by G proteins of the Gi/Go class and that this coupling is via a direct, membrane delimited pathway.
Metabotropic glutamate receptors mediate a post‐tetanic excitation of guinea‐pig hippocampal inhibitory neurones.
Authors: Miles R , Poncer J C
Published: December 2014

1. Inhibitory cell activity and inhibitory postsynaptic potentials impinging spontaneously on pyramidal cells were recorded in the CA3 region of hippocampal slices from guinea‐pig. We compared the effects on synaptic inhibition, of tetanic stimuli in the presence of antagonists of ionotropic excitatory amino acid receptors, and of application of agonists of metabotropic glutamate receptors. 2. Tetanic stimulation of afferent fibres caused an increase, of duration 0.5‐2.5 min, in the frequency of spontaneous Cl(‐)‐mediated IPSPs. Inhibitory cell firing increased due to a depolarization and a reduction of after‐hyperpolarizing potentials. 3. Tetanic stimulation induced, in some experiments, rhythmic bursts of IPSPs and transformed the firing pattern of some inhibitory cells from a discharge of single action potentials to rhythmic bursts of three to five action potentials. 4. Application of the metabotropic glutamate receptor agonist, trans‐1‐amino‐cyclopentane‐1,3‐dicarboxylic acid (tACPD), at concentrations from 3‐10 microM increased the frequency of spontaneous IPSPs. In some slices tACPD caused IPSPs to occur rhythmically. IPSP frequency did not continue to increase with concentrations of tACPD above 20 microM. 5. tACPD depolarized inhibitory cells and reduced after‐hyperpolarizing potentials. High concentrations (50‐100 microM) of tACPD excited inhibitory cells to potentials at which they no longer discharged fast action potentials. 6. Both tetanic stimulation and tACPD led to the appearance in pyramidal cell pairs of simultaneous IPSPs which were not previously observed, suggesting that the same group of inhibitory cells was excited in both cases. 7. Low concentrations of tACPD (3‐10 microM) enhanced IPSP responses to tetanic stimuli, while the effects of tetanic stimuli were occluded in the presence of high concentrations (20‐30 microM) of tACPD. 8. We suggest that activation of metabotropic glutamate receptors during tetanic stimulation leads to a post‐tetanic excitation of inhibitory cells that mediate Cl(‐)‐dependent IPSPs.
Inhibitory effects of histamine and bradykinin on calcium current in smooth muscle cells isolated from guinea‐pig ileum.
Authors: Beech D J
Published: December 2014

1. Single smooth muscle cells were isolated from the longitudinal muscle layer of the guinea‐pig ileum and within 10 h Ca(2+)‐currents (ICa) were recorded using the whole‐cell patch clamp technique. 2. Histamine (10 microMs) and bradykinin (BK, 1 microM) suppressed ICa; the effect had two phases: a rapid and transient suppression of ICa followed by a sustained suppression. Acetylcholine and substance P appeared to have similar effects but these were not investigated in detail. 3. The effects of histamine and BK on ICa were established by high intracellular concentrations of the Ca2+ buffer EGTA (30 mM) or 1,2‐bis(O‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA) (5 mM) in the absence of Ca2+ added to the pipette solution. When [Ca2+]i was strongly buffered to 125 or 190 nM by BAPTA‐Ca2+ mixtures in the pipette the transient suppression of ICa was blocked but the sustained effect still occurred. This indicated that the transient effect was caused by a rise in [Ca2+]i. The sustained effect, in contrast, did not seem to be caused by a rise in [Ca2+]i but did show Ca2+ dependence because it did not occur if [Ca2+]i was abnormally low. 4. Application of caffeine (10 mM) to deplete stored Ca2+ or intracellular heparin (1 mM) to block the action of D‐myo‐inositol 1,4,5‐trisphosphate (IP3) to release stored Ca2+ prevented the transient but not the sustained suppression of ICa. Heparin also blocked the transient Ca(2+)‐activated K+ current in response to histamine or BK. Both transient and sustained suppressions of Ca2+ channel activity were observed in the absence of extracellular Ca2+ when current was carried mostly by Na+ ions. 5. Intracellular guanosine 5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S; 10 or 100 microM) induced a gradual decline of ICa upon which transient decreases of current were superimposed. Histamine caused a larger than normal inhibition of ICa and no recovery occurred on wash‐out. Intracellular guanosine 5'‐O‐(2‐thiodiphosphate) (GDP‐beta‐S; 1 mM) abolished the effects of histamine and BK on ICa.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of hormones on potential difference and liquid balance across explants from proximal and distal fetal rat lung.
Authors: Krochmal‐Mokrzan E M , Barker P M , Gatzy J T
Published: December 2014

1. Fetal rat tracheas and lung buds form liquid‐filled cysts in submersion culture. The volume that accumulates in cysts is driven by active Cl‐ secretion. 2. We examined the effects, on these explants, of hormones that induce liquid absorption by fetal sheep lung in vivo. Explants were impaled with microelectrodes to measure potential difference (PD). Liquid was estimated from explant weight. 3. Water/dry weight ratio of lung buds and tracheas after 8 days in culture averaged 12 and 22. Exposure of triiodothyronine (T3) and hydrocortisone (HC) followed by a physiological dose of adrenaline on day 7 for 24 h or by a maximal dose of terbutaline on day 8 for 4 h induced a 35% decrease in water/dry weight ratio of distal buds but not tracheas. No hormone, or combination of two hormones, affected the ratio for tracheas or lung buds. 4. Basal PDs of tracheas (18.9 mV) and lung buds (3.7 mV) were increased about 50% by terbutaline. The terbutaline response was inhibited by bumetanide, but not by amiloride injected into the cysts. 5. T3 and HC pretreatment reduced basal PD by one‐third. Subsequent exposure to terbutaline raised the PD of hormone‐pretreated lung buds by more than 150%, a response that was blocked by amiloride, but was antagonized minimally by bumetanide. Responses of hormone‐pretreated tracheas were not different from those of untreated tracheas. 6. We conclude that: (a) absorption of liquid from lung buds is driven by an amiloride‐sensitive process (active Na+ transport?) and (b) only distal lung contributes to the adrenaline‐sensitive reabsorptive process required for perinatal adaptation to air breathing.
Calcium transients and calcium release in rat fast‐twitch skeletal muscle fibres.
Authors: Garcia J , Schneider M F
Published: December 2014

1. Calcium transients were recorded from cut segments of fast‐twitch rat skeletal muscle fibres stretched to 3.7‐4.0 microns per sarcomere and voltage clamped at a holding potential of ‐80 mV using the double Vaseline‐gap technique. Calcium transients were monitored simultaneously with the two calcium indicators antipyrylazo III (AP III) and fura‐2. AP III was used to record the calcium changes in response to 10‐200 ms depolarizing pulses to different membrane potentials while fura‐2 monitored the slow decay of the transient (during 16‐20 s) and the resting calcium concentration. Experiments were performed at 14‐17 degrees C. 2. For 50‐100 ms depolarizing pulses calcium transients were first detected between ‐30 and ‐20 mV in a total of twenty‐one fibres. The transients recorded with AP III showed a plateau for small pulses (‐20 mV) and a steady increase during stronger pulses (‐10 mV and more positive). Upon repolarization the transients decayed towards the baseline. The signal recorded simultaneously with fura‐2 showed a continuous increase of the transient during the pulses at all membrane potentials. The amplitude of the calcium transients for the large pulses could not be followed with fura‐2 due to saturation of the dye. 3. The signals obtained with both dyes were used to determine the kinetics of the calcium‐fura‐2 reaction inside the fibres. The mean values of the kinetic parameters were: the on rate constant (kon) = 5.1 x 10(8) M‐1s‐1, the off rate constant (koff) = 26 s‐1, and koff/kon (KD) = 69.7 nM. 4. The fast phase of decay of the calcium transients after the pulses was studied from the records obtained with AP III. For depolarizing pulses of the same duration, the rate of decay of the transients after the pulse was slower the stronger the depolarization. For pulses to the same membrane potential, the rate of decay was slower the longer the pulse duration. Both stimulating patterns indicated saturation of the removal system in the muscle fibres due to occupancy of slowly equilibrating myoplasmic calcium binding sites by released calcium. 5. The fast phase of decay of the signals obtained with AP III was well fitted with a model of the system for removing calcium from the myofilament space. 6. The rate of calcium release (Rrel) from the sarcoplasmic reticulum was calculated once the removal system was characterized in the same fibre.(ABSTRACT TRUNCATED AT 400 WORDS)
Observations on human tactile directional sensibility.
Authors: Olausson H , Norrsell U
Published: December 2014

1. The ability to tell the direction of a motion across the skin deserve attention for being an easily observed function which provides a sensitive test for disturbances of the peripheral and central nervous systems. The mode of operation, on the other hand, of this tactile directional sensibility is still uncertain. 2. The dependence of directional sensibility on the contact load and distance of movement of a blunt metal tip, has now been determined for the skin of the forearm of normal subjects with the two‐alternative forced‐choice method. The testing was done under two conditions: elbow bent or straight. Straightening of the arm always reduced the accuracy of the directional sensibility. It also caused measurable changes of cutaneous mechanical properties, which presumably decreased the reliability of afferent information about lateral distension. 3. The average accuracy of the directional sensibility was found to be correlated linearly to the logarithm of the contact load, and straightening of the arm decreased the accuracy for each load by corresponding amounts. Similar relationships were found between the accuracy and the distance of movement. 4. Straightening of the arm did not cause any significant average reduction of the contact threshold for point stimulation of the same receptive field. A consistently lowered contact sensitivity, however, was observed for some of the subjects, which may have contributed to the reduction of the directional sensibility in these cases. 5. Correct directional estimations of the movement of the metal tip were obtained for a distance which was a fifth of the shortest distance for a corresponding estimation of the movement of a frictionless stimulus. The findings thus indicated that the friction between a moving object and the underlying skin, which can be mediated via stretch‐sensitive cutaneous receptors, is critical for the determination of its direction of motion. 6. The present observations and previous observations by various authors are suggested to indicate that typical tactile directional sensibility depends on parallel processing of direction‐selective data, and spatial data expressed as a function of time.
ATP‐sensitive K+ channel modification by metabolic inhibition in isolated guinea‐pig ventricular myocytes.
Authors: Deutsch N , Weiss J N
Published: December 2014

1. ATP‐sensitive K+ (K+ATP) channels are believed to make an important contribution to the increased cellular K+ efflux and shortening of the action potential duration (APD) during metabolic inhibition, hypoxia, and ischaemia in the heart. The mechanisms by which the activity of the K+ATP channel is regulated during conditions of metabolic impairment are not completely clear. Extrinsic factors such as increased [ADP]i, acidosis, and stimulation of adenosine receptors appear to decrease the K+ATP channel's sensitivity to closure by [ATP]i. The purpose of this study was to determine whether the K+ATP channel itself is intrinsically altered by the processes associated with metabolic impairment. 2. Isolated guinea‐pig ventricular myocytes were metabolically inhibited in glucose‐free 1.8 mM Ca2+ Tyrode solution containing 9 microM rotenone and 0.9 microM carbonyl cyanide‐p‐trifluoromethoxyphenylhydrazone (FCCP) while recording unitary currents through K+ATP channels in cell‐attached patches. When K+ATP channel activity became maximal, the patch was excised (inside‐out) into 150 mM K+ bath solution containing different ATP concentrations. The Kd for suppression by [ATP]i ([ATP]i causing half‐maximal suppression of current through K+ATP channels) was markedly increased to 305 microM (n = 9) compared to patches excised from control myocytes not exposed to metabolic inhibitors (Kd = 46 microM, n = 28). 3. A [Ca2+]i‐dependent process was involved in K+ATP channel modification during metabolic inhibition. Removal of extracellular Ca2+ during metabolic inhibition led to an intermediate decrease in the ATP sensitivity of the K+ATP channels (Kd = 120 microM, n = 6). In myocytes that were pretreated with 10 microM ryanodine in addition to removing extracellular Ca2+, the reduction in ATP sensitivity was completely prevented (Kd = 23 microM, n = 6). 4. In inside‐out membrane patches excised from control non‐metabolically inhibited myocytes, elevated free [Ca2+]i (2 microM) did not alter the sensitivity of the K+ATP channel to closure by [ATP]i, suggesting that in metabolically inhibited myocytes elevated [Ca2+]i acted indirectly. K+ATP channel run‐down was found to increase the sensitivity of K+ATP channels to closure to [ATP]i (Kd = 16 microM, n = 13). 5. Inside‐out membrane patches excised from control non‐metabolically inhibited myocytes were also exposed to various proteases, phospholipases and other reagents that may be activated during metabolic inhibition. Trypsin and chymotrypsin treatment increased the Kd from 39 to 213 microM (n = 8) and 110 microM (n = 5), respectively. Calpain I had no apparent effect on the Kd.(ABSTRACT TRUNCATED AT 400 WORDS)
Cell volume regulation in rat thymocytes.
Authors: Arrazola A , Rota R , Hannaert P , Soler A , Garay R P
Published: December 2014

1. DIOA (dihydroindenyl‐oxy‐alkanoic acid), a potent inhibitor of the K(+)‐Cl‐ co‐transport system, fully blocked regulatory volume decrease (RVD) in swelled rat thymocytes, with an IC50 of 2.2 +/‐ 0.5 x 10(‐5) mol l‐1 (mean +/‐ S.D., n = 4). Conversely, RVD was resistant to quinine, quinidine, apamin, cetiedil, amiloride, bumetanide and DIDS (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonate). 2. DIOA‐sensitive RVD followed mono‐exponential kinetics, with t1/2 (half‐lifetime) of 1‐3 min and maximal capacity (Cmax) of about 55% of the initial cell swelling. Cmax and the initial rate of RVD (Vo) were both linear functions of the increase in cell volume. 3. RVD was: (i) slightly increased by replacing external Cl‐ by NO3‐, (ii) reversed by replacing external Na+ by K+ (in the presence of external Cl‐) and (iii) inhibited by cell K+ depletion. All these phenomena were blocked by DIOA (86 mumol l‐1). 4. Increased membrane potassium permeability by valinomycin was unable to accelerate RVD or RVD reversal. 5. In the presence of DIOA, thymocytes responded like osmometers (the relative cell volume was a linear function of the reciprocal of the relative osmolality) in a large range of osmolalities. 6. The results strongly suggest that RVD in rat thymocytes is mediated by the K(+)‐Cl‐ co‐transport system.
A possible role for endogenous peripheral corticotrophin‐releasing factor‐41 in the febrile response of conscious rabbits.
Authors: Milton N G , Hillhouse E W , Milton A S
Published: December 2014

1. The actions of peripheral corticotrophin‐releasing factor‐41 (CRF‐41) on the febrile responses of conscious rabbits induced by peripherally administered polyinosinic.polycytidylic acid (poly(I).poly(C)) have been studied using a CRF‐41 receptor antagonist (alpha‐helical CRF(9‐41) and anti‐CRF‐41 monoclonal antibodies. 2. Temperature responses were monitored continuously using rectal thermistor probes. Test substances were administered intravenously (i.v.), or for central CRF‐41 antagonism experiments, via an indwelling third ventricle cannula (I.C.V.). Blood samples were taken at time intervals from a marginal ear vein and plasma cortisol levels determined by radioimmunoassay. 3. Poly(I).poly(C) (2.5 micrograms/kg) stimulated a reproducible biphasic rise in body temperature with a lag phase of 45‐60 min and peaks at 90 and 225 min. 4. The febrile response to poly(I).poly(C) (2.5 micrograms/kg I.V.) was antagonized by blockade of peripheral CRF‐41 actions using either monoclonal anti‐CRF‐41 antibodies (2.5 mg/kg i.v.) or the CRF‐41 receptor antagonist (alpha‐helical CRF(9‐41); 25 micrograms/kg i.v.) administered 5 min prior to the pyrogen. 5. Centrally administered CRF‐41 receptor antagonist (2.5 micrograms/kg I.C.V.) failed to affect the febrile response to poly(I).poly(C) (2.5 micrograms/kg i.v.). 6. CRF‐41 immunoneutralization after the onset of temperature rises caused an immediate and significant defervescence. 7. In conclusion, these results suggest a modulatory pro‐pyretic role for endogenous peripheral CRF‐41 in the febrile responses to poly(I).poly(C).
Dual regulation of cation‐selective channels by muscarinic and alpha 1‐adrenergic receptors in the rabbit portal vein.
Authors: Inoue R , Kuriyama H
Published: December 2014

1. The excitatory actions of phenylephrine (Phe) and acetylcholine (ACh) on the smooth muscle of rabbit portal vein were investigated and compared by using whole‐cell and single channel configurations of the patch clamp technique, in combination with a modified concentration jump method. 2. At negative holding potentials with KCl (0.1 mM EGTA) electrodes, rapid applications of Phe (> 1 microM) and ACh (> 10 microM) both resulted in biphasic responses consisting of fast outward or inward currents and a long‐lasting inward current with an increased noise level. 3. The slow inward current was still recorded when the cell was dialysed with caesium aspartate solution complemented with 10 mM EGTA, in order to eliminate contributions of calcium‐dependent conductances (K+ and Cl‐ currents). Phe was more potent at activating the current than ACh. Ion replacement experiments revealed that both the Phe‐ and ACh‐induced slow inward currents are cation‐selective conductances (CS currents). 4. The I‐V relationships of the Phe‐ or ACh‐induced CS currents were similar both for the instantaneous peak and the steady state. The tail current analysis over a wide range of membrane potentials (‐150 to +100 mV) showed that depolarizations to very positive potentials (> +50 mV) from near the resting membrane potential (‐40 mV) can produce a several‐fold increase in the steady‐state activation of the CS currents, but the maximal activations were in most cases not observed even at +100 mV. 5. Externally applied Cd2+ produced a quick and reversible inhibition of both the Phe‐ and ACh‐induced CS currents. This inhibition seemed almost voltage independent and the concentrations of half‐inhibition were 100 and 129 microM for Phe and ACh, respectively. 6. Single channel activities were recorded in the presence of Phe or ACh using the outside‐out membrane patches. The unitary conductances and reversal potentials of the Phe‐ and ACh‐activated channels were 23 pS, +5.2 mV and 25 pS, +4.1 mV, respectively, and the open lifetimes evaluated for 50 microM Phe and 500 microM ACh were of similar order (the longer open times at ‐60 mV for Phe and ACh were 4.3 and 4.4 ms, respectively). In addition, the relative open probability (Po,rel) was no more than 0.2 in the voltage range of ‐100 to ‐30 mV for both 50 microM Phe and 500 microM ACh, suggesting low open probabilities of the Phe‐ and ACh‐activated CS channels near the resting membrane potential.(ABSTRACT TRUNCATED AT 400 WORDS)
Food stimulation of histidine decarboxylase messenger RNA abundance in rat gastric fundus.
Authors: Dimaline R , Sandvik A K , Evans D , Forster E R , Dockray G J
Published: December 2014

1. Histidine decarboxylase in the enterochromaffin‐like cells of the gastric corpus mucosa converts histidine to histamine which in turn stimulates gastric acid secretion. The control of histidine decarboxylase activity is poorly understood. We have examined how fasting and refeeding influence the abundance of the messenger RNA encoding histidine decarboxylase in the gastric corpus of the rat. 2. The polymerase chain reaction was used to generate a probe for detection of histidine decarboxylase messenger RNA in Northern and slot blots of total RNA from the gastric corpus of rats fasted for up to 48 h, or fasted and then refed. A gastrin monoclonal antibody was used to neutralize the action of endogenous gastrin. 3. Fasting progressively reduced histidine decarboxylase messenger RNA abundance by 3‐ to 4‐fold after 48 h. Refeeding induced a rapid increase in histidine decarboxylase messenger RNA abundance which was detectable after 30 min. 4. There was a significant correlation between histidine decarboxylase messenger RNA abundance and plasma gastrin. Administration of gastrin antibody inhibited the increase in histidine decarboxylase activity after 6 h refeeding, but not after refeeding for 30 min. 5. The results suggest that histamine‐mediated changes in postprandial acid secretion depend on control of histidine decarboxylase mRNA levels, and that gastrin regulates production of this enzyme in the rat over periods of a few hours.