bluuebunny/crossref_metadata_2025 huggingface dataset:
Abnormality of superior mesenteric artery blood flow responses in human sympathetic failure.
Authors: Chaudhuri K R , Thomaides T , Mathias C J
Published: December 2014

1. Systemic and regional haemodynamic responses, including superior mesenteric artery blood flow, were measured during stimuli which increase sympatho‐neural activity in age‐matched normal subjects (controls) and in two groups of patients with sympathetic failure (pure autonomic failure and multiple system atrophy). The stimuli included the pressor tests (mental arithmetic, cutaneous cold and isometric exercise) and head‐up tilt. 2. In the controls, the blood pressure did not rise in some during mental arithmetic, but rose in all subjects during cutaneous cold and isometric exercise and was maintained during head‐up tilt. In sympathetic failure patients, blood pressure was unchanged during each pressor test and fell during head‐up tilt. 3. In the controls, superior mesenteric artery blood flow did not fall significantly during mental arithmetic but fell (with a corresponding rise in calculated superior mesenteric artery vascular resistance), during cutaneous cold, isometric exercise and head‐up tilt. In sympathetic failure patients, there were no changes in superior mesenteric artery blood flow and vascular resistance during the pressor tests and head‐up tilt. 4. There were no changes in cardiac index or forearm blood flow during each pressor test in both controls and patients. Cardiac index fell and forearm vascular resistance rose during head‐up tilt in the controls only. 5. In conclusion, active constriction of the superior mesenteric artery occurs in normal subjects during sympatho‐neural activation induced by stimuli such as cutaneous cold, isometric exercise and head‐up tilt. This does not occur in patients with sympathetic failure and probably contributes to postural hypotension, emphasizing the role of the splanchnic vascular bed in overall blood pressure control. This study confirms the necessity of integrity of sympathetic pathways in the neural control of the splanchnic vascular bed.
Myofibrillar fatigue versus failure of activation during repetitive stimulation of frog muscle fibres.
Authors: Edman K A , Lou F
Published: December 2014

1. Single fibres isolated from the anterior tibialis muscle of Rana temporaria (temperature, 2‐5 degrees C; sarcomere length, 2.10 microns) were fatigued using two separate protocols that led to different degrees of depression of tetanic force. Under control conditions the fibre was stimulated to produce a 1 s fused isometric tetanus at 300 s intervals. A moderate degree of fatigue (tetanic force reduced to 70‐80% of the control value) was produced by decreasing the intervals between tetani to 15 s (‘fatiguing protocol 1’). A more pronounced depression of tetanic force (to 40‐50% of the control value) was produced by evoking a single twitch at 1‐2 s intervals (‘fatiguing protocol 2’). 2. Fatiguing protocol 1 reduced the contracture response to submaximal and supramaximal concentrations of caffeine (3‐15 mM) in proportion to the decrease in tetanic force. These results support the view that fatiguing stimulation according to protocol 1 leads to a true ‘myofibrillar fatigue’ with no failure of activation of the muscle fibre. 3. Fatiguing protocol 2 reduced the amplitudes of isometric twitch and tetanus to below 10 and 50% of the control values, respectively. By contrast, the maximal contracture response to caffeine (15 mM) was depressed by merely 2‐3% of its prefatigue value. 4. Force and instantaneous fibre stiffness were recorded simultaneously during twitch and tetanus as fatigue was induced by protocol 2. During the initial part of fatigue (tetanic force reduced by 25% of control) stiffness was reduced by merely 9% in accordance with previous measurements during fatigue induced by protocol 1. However, with further depression of twitch and tetanus by protocol 2 there was a marked reduction of fibre stiffness. These results, together with the findings reported under point 3, strongly suggest that at an advanced state of fatigue induced by protocol 2 the decrease in active force is largely due to failure of activation of the contractile system. 5. Muscle fibres were quickly frozen for electron microscopical examination after shortening below slack length (to approximately 1.6 microns sarcomere spacing) during tetanic stimulation. In non‐fatigued fibres, and in fibres fatigued according to protocol 1, the myofibrils exhibited a straight appearance throughout the preparation suggesting that the entire volume of the fibre was properly activated. In fibres fatigued by protocol 2, on the other hand, only the most peripheral layers of myofibrils remained straight after shortening, whereas the centre of the fibre showed marked waviness indicating failure of the inward spread of activation in this case.
Substrate influences rat osteoclast morphology and expression of potassium conductances.
Authors: Arkett S A , Dixon S J , Sims S M
Published: December 2014

1. We studied the electrophysiological properties of freshly isolated rat osteoclasts using the whole‐cell configuration of the patch‐clamp technique. Membrane currents were recorded from cells plated on three substates: dentine, type I collagen and glass. 2. Based on their morphology, we defined two categories of osteoclasts. ‘Rounded’ osteoclasts were dome‐shaped and lacked lamellipodia. ‘Spread’ osteoclasts were flattened and had lamellipodia. The proportion of ‘rounded’ osteoclasts was significantly greater when cells were plated on dentine or type I collagen than when cells were plated on glass. 3. ‘Spread’ osteoclasts expressed an inwardly rectifying K+ conductance regardless of the substrate on which they were plated. 4. ‘Rounded’ osteoclasts, on all substrates, expressed a transient, outwardly rectifying conductance that was selective for K+ based on: reversal of deactivation tail currents at ‐74 mV; a 60 mV shift in tail current reversal potential for 10‐fold change in [K+]o; and blockade of outward current by extracellular 4‐aminopyridine, charybdotoxin, and intracellular Cs+. The outward K+ current had an activation threshold of approximately ‐50 mV, with half‐activation at ‐29 mV. The current also exhibited voltage‐dependent inactivation, with half‐inactivation at approximately ‐40 mV. 5. Outward K+ current in ‘rounded’ osteoclasts was reduced when extracellular Ca2+ was removed and upon addition of Ni2+, but was unaffected by Cd2+ or nifedipine. 6. ‘Rounded’ osteoclasts had large whole‐cell capacitance for their apparent surface area. Capacitance was positively correlated with K+ conductance. The additional surface membrane we detected through capacitance measurements may be the ‘ruffled border’ of actively resorbing osteoclasts. 7. We conclude that substrate influences the expression of osteoclast phenotype, as defined by morphology and K+ conductances. ‘Rounded’ osteoclasts express an outwardly rectifying K+ conductance, with no apparent inwardly rectifying K+ conductance. In contrast, 'spread’ osteoclasts exhibit an inwardly rectifying K+ conductance with no outwardly rectifying K+ conductance. The 'spread’ phenotype may represent a motile phase, while the ‘rounded’ phenotype may represent a resorptive phase of osteoclastic activity.
NMDA receptor‐mediated rhythmic bursting activity in rat supraoptic nucleus neurones in vitro.
Authors: Hu B , Bourque C W
Published: December 2014

1. Intracellular recordings were obtained from 112 supraoptic nucleus magnocellular neurosecretory cells (MNCs) in superfused explants of rat hypothalamus maintained in vitro. The effects of glutamate receptor agonists and antagonists were examined at 32‐34 degrees C. 2. In control solutions, spontaneously active (> 5 Hz) phasic or continuous neurones showed interspike interval distributions slightly skewed toward short intervals, but did not feature pauses in the 0.4‐2 s range. Current injection to alter the rate of cell discharge shifted the histograms according to the mean firing rate, but failed to induce intermittent pauses in the 0.4‐2 s range. 3. Application of N‐methyl‐D‐aspartate (NMDA) induced a mode of firing in which bimodal interspike interval distributions reflected a high incidence of clusters of short interspike intervals (0.5‐1.5 s) recurring every 1‐3 s. In contrast, firing evoked by application of D,L‐alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxalone propionic acid (AMPA) was not associated with a clustering of impulse discharge. 4. The putative endogenous excitatory amino acid transmitters L‐glutamate, L‐aspartate and quinolinate all mimicked the effects of NMDA. Clustered spiking responses to these agents were reversibly blocked by D,L‐2‐amino‐5‐phosphono‐valerate (APV), but not by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX). In contrast, the non‐NMDA receptor ligands kainate and quisqualate caused CNQX‐sensitive increases in firing rate, but these responses were not associated with the appearance of clustered activity. 5. When applied to cells showing negative resting potentials (< ‐70 mV), or to neurones hyperpolarized by current injection, responses to NMDA consisted of rhythmic (approximately 1 Hz) voltage oscillations associated with bursts of spike discharge. In the presence of TTX, NMDA could induce subthreshold voltage oscillations in the absence of action potentials. 6. Application of a voltage clamp to potentials between ‐75 and ‐55 mV during rhythmic bursting responses failed to reveal any rhythmic oscillation of the membrane current. In all cases, rhythmic bursting activity resumed upon returning to the current‐clamp mode. 7. Rhythmic bursting responses to NMDA application were abolished in Mg(2+)‐free solutions, suggesting that the voltage dependence of NMDA channels served to promote regenerative voltage changes throughout the cycle. The NMDA‐induced current itself, however, did not appear to decrease with time, suggesting that a distinct, outward current, was necessary to initiate the repolarizing phase of each cycle.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of a transient K+ current in chemoreceptor cells of rabbit carotid body.
Authors: López‐López J R , De Luis D A , Gonzalez C
Published: December 2014

1. Adult rabbit carotid body chemoreceptor cells, enzymatically dispersed and short‐term cultured, exhibit an inactivating outward K+ current that is reversibly inhibited by low PO2. In the present work we have characterized the biophysical and pharmacological properties of this current using the whole‐cell voltage clamp recording technique. 2. Inactivating current was recorded after blockage of Ca2+ currents with extracellular Co2+, Cd2+, or after complete washing out of Ca2+ channels. 3. The threshold of activation of this inactivating current was about ‐40 mV. Current activated very quickly (mean rise time 4.8 +/‐ 0.42 ms at +60 mV) but inactivated more slowly. Inactivation was well fitted by two exponentials with time constants of 79.7 +/‐ 6.6 and 824 +/‐ 42.8 ms (at +40 mV). The inactivation process showed a little voltage dependence. 4. The steady‐state inactivation was well fitted by a Boltzman function. Inactivation was fully removed at potentials negative to ‐80 mV and was complete at voltages near ‐10 mV; 50% inactivation occurred at ‐41 mV. 5. Recovery from inactivation had several components and was voltage dependent. Initial recovery was fast, but full recovery, even at ‐100 mV, required more than 30 s. 6. Inactivating current was selectively blocked by 4‐aminopyridine (4‐AP), in a dose‐dependent manner (IC50, 0.2 mM). The duration of chemoreceptor cells action potentials was augmented by 1 mM 4‐AP from 2.3 +/‐ 0.36 to 7.0 +/‐ 0.25 ms at 0 mV. Tetraethylamonium (TEA), at concentrations above 5 mM, blocked inactivating and non‐inactivating components of the whole K+ current. 7. Inactivating current was modulated by cyclic AMP (cAMP). Bath application of 2 mM dibutyryl cAMP reduced peak amplitude by 18.7 +/‐ 2.9% (at +30 mV) and slowed down the rise time of the current. The effect was not voltage dependent. Forskolin (10‐20 microM) also affected inactivating current, by accelerating the inactivation process. In the same preparations neither dibutyryl cAMP nor forskolin affected Ca2+ currents. 8. It is concluded that modulation of K+ channels by cAMP might play a physiological role potentiating the low PO2 inhibition of K+ channels.
Correlations between myosin heavy chain isoforms and mechanical parameters in rat myometrium.
Authors: Hewett T E , Martin A F , Paul R J
Published: December 2014

1. The relations between mechanical parameters and myosin heavy chain isoforms were studied in myometrial smooth muscle from ovariectomized rats (O) and oestrogen‐treated, ovariectomized rats (E). 2. Treatment of the rats for three days with beta‐oestradiol (2 micrograms kg‐1 day‐1) 2‐4 weeks postsurgery, produced maximal changes in uterine mass and myosin content of approximately threefold. 3. Myosin heavy chain isoform SM1 (204 kDa) was increased from 65.5 +/‐ 0.8% to 72.9 +/‐ 0.6% of the total isoform species (P < 0.001, n = 24, O and E respectively) after oestrogen treatment. 4. To avoid complications associated with activation processes, mechanical parameters were measured in permeabilized myometrial fibre bundles activated at a calcium concentration of 12.6 microM. After oestrogen treatment the maximum velocity of shortening (Vmax) measured by the slack test increased from 0.044 +/‐ 0.006 of the reference length (Lo) s‐1 to 0.101 +/‐ 0.006 Lo s‐1, and maximal isometric force (Pmax) increased from 23.3 +/‐ 4.4 mN mm‐2 to 74.1 +/‐ 13.9 mN mm‐2 (P < 0.001, n = 24, respectively). Series elasticity and the half‐time to peak force were not significantly altered. 5. Both Vmax and Pmax correlated significantly with percentage SM1 in O and E fibre bundles (r = 0.61 and 0.56, n = 48 fibres; or r = 0.87 and 0.89, n = 8 grouped data per rat). Vmax, however, was only weakly correlated with Pmax (r = 0.39, n = 48). 6. To assess the relative significance of the correlation between Vmax and the percentage of SM1 and that between Vmax and Pmax, we used a multiple regression analysis with the model Vmax = intercept + beta 1 x % SM1 + beta 2 x Pmax, where intercept, beta 1 and beta 2 are regression parameters. This analysis (n = 48) indicated that Vmax was significantly dependent on the percentage of SM1 (P < 0.0002) but not on Pmax (P < 0.61). 7. There were no significant differences in the levels of myosin light chain phosphorylation between O and E fibre bundles, indicating that light chain phosphorylation is unlikely to be the basis for the differences in mechanical parameters demonstrated by these fibres.
Electrophysiology of guinea‐pig supraoptic neurones: role of a hyperpolarization‐activated cation current in phasic firing.
Authors: Erickson K R , Ronnekleiv O K , Kelly M J
Published: December 2014

1. Immunocytochemically identified magnocellular neurosecretory cells (MNCs) in the guinea‐pig supraoptic nucleus (SON) were studied using the in vitro intracellular recording technique. Cells were identified as containing arginine vasopressin (AVP) or oxytocin (OT) following recordings made with biocytin‐filled electrodes. Both AVP and OT MNCs demonstrated a fusiform or pyramidal shape (15‐20 microns by 26‐39 microns), with two to three processes. There were no significant differences in the proportion of AVP and OT cells in the retrochiasmatic (caudal) versus the rostral slices. 2. No significant differences in passive membrane properties were observed between AVP and OT cells, except that AVP cells exhibited a significantly broader action potential width (1.51 +/‐ 0.1 ms, n = 11) than did OT cells (1.01 +/‐ 0.08 ms, n = 7). 3. Firing patterns were recorded for 100 MNCs, 41% of which fired in a phasic manner (repeated clustering of action potentials into bursts). Of the seventy‐seven cells which were immunocytochemically identified, only AVP‐containing MNCs displayed phasic firing. Phasic firing occurred only in MNCs demonstrating a depolarizing potential which followed hyperpolarizing after‐potentials (HAPs). The presence of the depolarizing potential was not always associated with phasic firing, however, as both OT cells and non‐phasic AVP cells sometimes exhibited a depolarizing potential. 4. In 160 MNCs examined for the presence of the time‐dependent inward rectification (TDR in current clamp, or Ih in voltage clamp), a significant difference in the proportion of cells expressing the Ih was observed in the two cell types. The Ih was expressed in forty‐five of fifty‐four AVP MNCs (83%) and in six of fifteen OT MNCs (40%). No significant association was found with firing pattern. 5. The Ih exhibited properties similar to those found in other CNS and peripheral tissues. It appeared on steps to potentials more hyperpolarized than ‐65 mV. It was augmented by raising the extracellular potassium concentration, blocked by 2 mM CsCl, and insensitive to 100‐500 microM BaCl2. Activation followed a single exponential, and the time constant of activation was voltage dependent. 6. The adenylate cyclase activator forskolin increased the Ih and shifted its activation curve to more depolarized levels. In cells recorded for several hours, the Ih varied in amplitude, suggesting intrinsic modulation, possibly by intracellular second messenger systems. The Ih in guinea‐pig SON MNCs appears to serve an excitatory role, bringing cells closer to firing threshold.
Mechanisms underlying chemoreceptor inhibition induced by atrial natriuretic peptide in rabbit carotid body.
Authors: Wang W J , He L , Chen J , Dinger B , Fidone S
Published: December 2014

1. Previous studies in our laboratory revealed the presence of atrial natriuretic peptide (ANP) in preneural chemosensory type I cells of the cat carotid body, and demonstrated that submicromolar concentrations of the peptide inhibited carotid sinus nerve (CSN) activity evoked by hypoxia. In the present study, we have evaluated the role of the cyclic nucleotide second messenger, cyclic GMP (cGMP), and the involvement of type I cells in rabbit chemosensory inhibition. 2. Submicromolar concentrations of the potent ANP analogue, APIII, greatly elevated both the content and release of cGMP from the carotid body. Denervation experiments confirmed earlier immunocytochemical studies which suggested that APIII‐induced cGMP production occurs almost exclusively in type I cells; these experiments also indicate that both the sympathetic and sensory innervation to the carotid body exert a trophic influence on the metabolism of this second messenger. 3. Submicromolar concentrations of APIII inhibited the CSN activity evoked by hypoxia (79.8 +/‐ 3.2% (mean +/‐ S.E.M.) inhibition with 100 nM APIII) and nicotine (74.5 +/‐ 3.6% inhibition with 100 nM APIII), but did not affect basal CSN activity established in 100% O2‐equilibrated superfusion solutions. 4. The biologically inactive analogue of ANP, C‐ANP, failed to produce CSN inhibition; however, the inhibitory effects of APIII were mimicked by cell‐permeant analogues of cGMP (dibutyryl‐cGMP and 8‐bromo‐cGMP, 2 mM), which likewise did not alter basal CSN activity. Because we found that unmodified cGMP was an ineffective inhibitor of CSN activity, our data suggest that APIII inhibition is mediated intracellularly by cGMP produced within the type I cells. 5. APIII does not inhibit the CSN activity produced by 20 mM K+ (in zero Ca2+ media), which very probably results from direct depolarization of the sensory nerve terminals. 6. Catecholamine release from the carotid body evoked by hypoxia is likewise not altered by APIII (100 nM). 7. The data are consistent with the notion that APIII and analogues of cGMP alter the release of excitatory and/or inhibitory transmitters from chemosensory type I cells in the carotid body.
Ca2+ cycling between sarcoplasmic reticulum and mitochondria in rabbit cardiac myocytes.
Authors: Bassani J W , Bassani R A , Bers D M
Published: December 2014

1. Shortening and intracellular Ca2+ (Ca2+i) transients were measured in isolated rabbit ventricular myocytes during paired contractures induced by rapid application of 10 mM caffeine. 2. Caffeine‐induced contractures relax despite maintained presence of caffeine. In control solution, a second phasic caffeine contracture failed to appear, unless the sarcoplasmic reticulum (SR) was refilled by a series of electrically stimulated twitches during the interval between caffeine exposures. 3. The relaxation of caffeine‐induced contractures in 0 Na(+)‐0 Ca2+ solution has previously been shown to rely on mitochondrial Ca2+ uptake and sarcolemmal Ca2(+)‐ATPase. Thus, a second caffeine contracture (T2) while still in 0 Na(+)‐0 Ca2+ was greatly reduced compared to the first one (T1). However, the amplitude of T2 increased exponentially with the time interval, attaining a maximum of approximately 50% of T1 for an interval of 180‐300 s, with a time constant (tau) of 41.2 s. Similar results were found for Ca2+i transients (tau = 45 s). 4. Inhibition of the mitochondrial Ca2+ uptake by the oxidative phosphorylation uncoupler, FCCP during T1 dramatically depressed T2. On the other hand, inhibition of the sarcolemmal Ca2(+)‐ATPase (by increasing extracellular Ca2+ concentration, [Ca2+]o) resulted in increase of T2. Spermine inclusion during T1 also increased T2, possibly by an increase of mitochondrial Ca2+ uptake. 5. We conclude that Ca2+ taken up by mitochondria during the decline of T1 moves back to the SR after caffeine is removed, with a tau approximately 40 s. 6. Partial intracellular Na+ depletion by prolonged (3 min) perfusion with 0 Na(+)‐0 Ca2+ solution before T1 (a) accelerated relaxation and [Ca2+]i decline during T1, and (b) slowed, but did not abolish, the recovery of T2 as the interval was increased. This effect was particularly pronounced when choline was used instead of Li+ as the Na+ substitute. 7. We further conclude that the mitochondrial Na(+)‐Ca2+ antiporter influences the rate of net Ca2+ uptake by mitochondria and is also important in Ca2+ efflux from mitochondria during rest.
Confocal microfluorimetry of Ca2+ signals evoked in Xenopus oocytes by photoreleased inositol trisphosphate.
Authors: Parker I , Ivorra I
Published: December 2014

1. The subcellular characteristics of inositol 1,4,5‐trisphosphate (InsP3)‐induced Ca2+ liberation were studied in Xenopus oocytes by the use of confocal microfluorimetry to monitor Ca2+ signals from minutely localized region of the cell in response to photorelease of InsP3 from a caged precursor. 2. Photorelease of increasing amounts of InsP3 by progressively longer light flashes evoked transient Ca2+ responses that appeared abruptly at a certain threshold duration, and then grew steeply over a narrow range of flash durations to reach a maximum. Further lengthening of flash duration gave no increase in size of the Ca2+ signals, but their rate of rise continued to increase and their duration became longer. Simultaneous measurements of Ca(2+)‐activated Cl‐ currents showed a slightly higher threshold than the Ca2+ signal, and a more graded dependence upon flash duration. 3. The threshold flash durations required to evoke Ca2+ and membrane current signals grew by more than 100‐fold as the area of the oocyte exposed to photolysis light was reduced from a square of 140 microns to 5 microns. 4. Ca2+ signals evoked by photoreleased InsP3 began following a dose‐dependent latency that was as long as several seconds with low intensity light, but shortened to about 50 ms at maximum intensity. The extrapolated minimum latency with infinite photorelease of InsP3 was about 30 ms. 5. InsP3‐evoked membrane currents began 30 ms or longer after the corresponding Ca2+ signals, whereas currents evoked by photorelease of Ca2+ from a caged precursor began within 5 ms of the onset of the light flash. 6. No differences in duration of InsP3‐evoked Ca2+ signals were apparent when the confocal measuring spot was positioned close to the plasma membrane or about 10 microns more deeply into the oocyte. At both locations the Ca2+ signals were more prolonged than the associated membrane current signals. 7. Ca2+ signals to a test light flash were suppressed for about 2 s following a conditioning suprathreshold flash, but recovered almost completely after 6 s. The associated membrane current signals were facilitated at short intervals, suppressed at intervals between 0.5 and 3 s, and subsequently recovered more slowly than the Ca2+ signals. 8. Photorelease of InsP3 during 30 s exposures of low intensity evoked trains of repetitive Ca2+ spikes. The overall amplitudes of these responses changed little with increasing in frequency, and became smaller and superimposed on a more sustained elevation of Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes in contractile properties by androgen hormones in sexually dimorphic muscles of male frogs (Xenopus laevis).
Authors: Regnier M , Herrera A A
Published: December 2014

1. Male frogs (Xenopus laevis) were castrated then given either empty or testosterone‐filled implants to produce animals with low or high levels of circulating testosterone. Eight weeks later the contractile properties of an androgen‐sensitive forelimb flexor, the flexor carpi radialis muscle (FCR), were measured in vitro. Another forelimb flexor muscle, the coracoradialis, and a hindlimb muscle, the iliofibularis, were analysed similarly. 2. Plasma testosterone levels were 0.9 +/‐ 0.3 ng/ml (+/‐ S.E.M.) in castrated frogs with blank implants (C) and 61.3 +/‐ 4.7 ng/ml in castrates with testosterone implants (CT). Unoperated males, sampled at various times of the year, ranged between 10.8 and 51.0 ng/ml. 3. With direct electrical stimulation of the FCR, contraction time of the isometric twitch was not affected by testosterone levels. Relaxation times were affected, however. Half‐ and 90% relaxation times were 27 and 42% longer, respectively, for CT compared to C muscles. 4. Testosterone also had no effect on the contraction time of twitches elicited by stimulation of the FCR nerve. Half‐ and 90% relaxation times were 51 and 76% longer, respectively, for CT compared to C muscles. 5. Tetanus tension, elicited by direct stimulation of the FCR at 50 Hz, was 86% greater in CT compared to C muscles. The average cross‐sectional area of FCR muscle fibres was 84% greater in CT muscles. These results implied that testosterone treatment had no effect on specific muscle tension. 6. Stimulation of the FCR nerve at 50 Hz resulted in 53% less tension than the same stimulus applied directly to CT muscles. In C muscles the difference was only 14%. This suggested that testosterone treatment reduced synaptic efficacy. 7. In CT muscles, direct or nerve stimulation of fibres in the shoulder region of the FCR elicited twitches that contracted and relaxed more slowly than fibres in the elbow region. In C muscles there was no difference in contraction or relaxation time between fibres in the shoulder and elbow regions. 8. Testosterone treatment had little effect on contraction and relaxation times or tension levels of coracoradialis or iliofibularis muscles.
Ca(2+)‐dependent K+ channels of high conductance in smooth muscle cells isolated from rat cerebral arteries.
Authors: Wang Y , Mathers D A
Published: December 2014

1. Cerebrovascular smooth muscle cells (CVSMCs) were dispersed from cerebral arteries of adult rats using collagenase and trypsin. The extracellular patch clamp technique was used to study single calcium‐activated potassium channels, KCa+ channels, in these cells at 21‐23 degrees C. 2. Whole‐cell, current clamp recordings showed that isolated CVSMCs possessed a mean resting potential of ‐41 +/‐ 7.4 mV (n = 69), an input resistance of 3.2 +/‐ 0.49 G omega (n = 20) and a capacitance of 24 +/‐ 2.3 pF (n = 7). 3. Inside‐out patches displayed a calcium‐dependent potassium channel, KCa+ channel, of mean conductance 207 +/‐ 10 pS (n = 16) and potassium permeability 3.9 x 10(‐13) cm s‐1 (n = 16) in symmetrical 140 mM K+ solutions. No substate conductance level was evident. 4. This channel was highly selective for K+ over Na+ or Cs+ (permeability ratio PNa/PK < 0.05; PCs/PK < 0.05, n = 5 patches in each case). Cs+ caused a voltage‐dependent block of the open channel. 5. Channel openings were detected at a threshold level of free internal calcium, [Ca2+]i = 10(‐8) M, and channels were open half of the time at [Ca2+]i = 2.3 x 10(‐5) M (membrane potential, Vm = +40 mV, n = 5). Over the probable physiological range of [Ca2+]i, the open probability of the KCa+ channel increased with the second power of calcium concentration. 6. Open time distributions were well fitted by the sum of two exponential terms, showing the occurrence of at least two kinetically distinguishable open states. Raising [Ca2+]i increased the time constant of the slow exponential component, but had no effect on that of the fast component. 7. At [Ca2+]i < 5 x 10(‐5) M, a 14 mV depolarization in membrane potential resulted in an e‐fold increase in the probability of KCa+ channels adopting an open state (n = 5). The slow time constant of the open time distributions also increased on membrane depolarization. 8. Tetraethylammonium ions applied to the cytoplasmic membrane face caused a reversible, dose‐dependent reduction in current flow through the KCa+ channel. This block was characterized by a dissociation constant of 0.83 +/‐ 0.09 mM at Vm = +40 mV and [Ca2+]i = 10(‐4) M (n = 5). 9. The lower calcium sensitivity and higher sensitivity to tetraethylammonium block distinguish this from other large conductance KCa+ channels in smooth muscle cells.
Ca2+ and Sr2+ activation properties of skinned muscle fibres with different regulatory systems from crustacea and rat.
Authors: West J M , Stephenson D G
Published: December 2014

1. The contractile activation properties of long‐ (sarcomere length (SL) > 6 microns) and short‐ (SL < 4 microns) sarcomere fibres from the claw muscle of the yabby (freshwater crustacean, Cherax destructor) and the fast‐ and slow‐twitch fibres from the rat have been investigated using single skinned muscle fibres activated in solutions containing Ca2+ or Sr2+ or both Ca2+ and Sr2+. 2. Sr2+ could not fully activate the contractile apparatus of either the long‐ or the short‐sarcomere yabby preparations and the force‐pSr curves for both fibre types were biphasic in shape. 3. The long‐ and short‐sarcomere fibres from the yabby differed in their Ca(2+)‐ and Sr(2+)‐activation properties. Thus the long‐sarcomere fibres required a significantly lower [Ca2+] to produce 10% maximum force, had Ca(2+)‐activation curves which were significantly shallower, and had a significantly higher ratio between maximum Sr(2+)‐ and maximum Ca(2+)‐activated force than the short‐sarcomere fibres. 4. Simultaneous activation with Ca2+ and Sr2+ showed a synergistic effect in the rat muscle fibres where Sr2+ could fully replace Ca2+ in activation. In contrast the results with the long‐ and short‐sarcomere fibres from the yabby showed that in some functional states Sr2+ binds but cannot (or can only partially) activate the regulatory system while in others Sr2+ can fully replace Ca2+ in activating contraction. 5. The synergistic effect between Sr2+ and Ca2+ in mammalian muscle could be quantitatively explained if all regulatory sites involved in contractile activation have a similar value for the ratio between their affinity for Ca2+ and Sr2+. 6. Three distinguishable functional states (based on the fibre's ability to be activated by Sr2+ and Ca2+) were identified in the long‐sarcomere fibres from the yabby: one where both Ca2+ and Sr2+ were able to activate contraction and had a relatively high sensitivity to Sr2+; one where both Ca2+ and Sr2+ were able to activate contraction but where the sensitivity to Sr2+ was lower and was more sensitive to a decrease in ionic strength; and one where Sr2+ binding to the regulatory system could not activate contraction. Equivalent states of the three described for the long‐sarcomere fibres were also found in the short‐sarcomere preparations. However, the short‐sarcomere fibres had, in addition, a fourth state which was characterized by the ability of Sr2+ to activate contraction at reduced ionic strength but not at standard ionic strength.(ABSTRACT TRUNCATED AT 400 WORDS)
Selective block of specific K(+)‐conducting channels by diphenylamine‐2‐carboxylate in turtle colon epithelial cells.
Authors: Richards N W , Dawson D C
Published: December 2014

1. The conduction and gating properties of K(+)‐conducting channels were studied in isolated turtle colon cells in an attempt to identify the single channels responsible for specific components of the macroscopic conductance of the basolateral membrane. Three types of Ca(2+)‐activated channel were identified, two of which were selective for K+ over Na+ and a third which was selective for monovalent cations over anions, but did not discriminate between K+ and Na+. 2. One of the K(+)‐selective channels was a large‐conductance ‘maxi’ K+ channel. A second was characterized by a lower conductance and pronounced inward rectification. 3. The inward‐rectifying K+ channel was selectively blocked by diphenylamine‐2‐carboxylate (DPC). Neither the maxi K+ channel nor a previously identified K(+)‐selective channel thought to be activated by cell swelling was affected by this compound. DPC also blocked the non‐selective cation channel. 4. An inward‐rectifying, DPC‐sensitive current was prominent in whole cell‐recordings, and DPC blocked basolateral K+ currents in colonic cell layers apically permeabilized with amphotericin‐B. In addition, the compound blocked active Na+ absorption. 5. The selective block of a class of epithelial K+ channels by DPC may be a useful tool for determining the contribution of this specific subpopulation to macroscopic conductance and transepithelial salt transport.
Characterization of synaptically elicited GABAB responses using patch‐clamp recordings in rat hippocampal slices.
Authors: Otis T S , De Koninck Y , Mody I
Published: December 2014

1. Tight‐seal, whole‐cell voltage clamp recording techniques were used to characterize monosynaptically evoked GABAB currents in adult rat brain slices maintained at 34‐35 degrees C. Responses were recorded from granule cells of the dentate gyrus following the blockade of 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX)‐, D‐2‐amino‐5‐phosphonovaleric acid (D‐AP5)‐ and picrotoxin‐sensitive fast synaptic transmission, so that the remaining synaptic currents could be studied in isolation. 2. Under these conditions, stimulation in the molecular layer elicited a slow outward current which was blocked by the selective GABAB antagonist CGP 35348 in a concentration‐dependent manner (200‐800 microM). This current was absent in recordings made with pipettes containing 10‐15 mM of the lidocaine derivative QX‐314 or when caesium was substituted for K+. 3. Increasing the [K+]o e‐fold (from 2.5 to 6.8 mM) shifted the reversal potential of the GABAB current from ‐97.9 to ‐73.2 mV, as predicted by the Nernst equation. Peak conductance was constant, but in 6.8 mM [K+]o at voltages hyperpolarized to EK (equilibrium potential for potassium), a small outward rectification was evident. 4. The time course of the current could be described by fourth‐power exponential activation kinetics with double exponential inactivation. At 34‐35 degrees C, the average activation time constant (tau m) was 45.2 ms, while the two inactivation time constants (tau h1 and tau h2) were 110.2 and 516.2 ms, with corresponding weighting factors (wh1 and wh2) of 0.84 and 0.16, respectively. The Q10 (temperature coefficient) values for these time constants were between 1.82 and 2.31. Neither tau m, nor tau h1 and tau h2 were voltage dependent in the range from ‐45 to ‐95 mV. 5. Paired‐pulse depression of the GABAB current was studied by giving identical conditioning and test stimuli over a wide range (50‐5000 ms) of interstimulus intervals (ISIs). The maximal depression (48%) occurred at 200 ms ISI, and the depression lasted for over 5 s. The magnitude of paired‐pulse depression was not dependent on the postsynaptic membrane potential. 6. Application of the competitive antagonist CGP 35348 such that the peak current was diminished by approximately 50% had no effect on the activation or inactivation kinetics of the current. Similarly, during paired‐pulse depression the kinetics of test currents were identical to those of conditioning currents. These findings support the hypothesis that the mechanism responsible for paired‐pulse depression involves a reduction in neurotransmitter release without postsynaptic alterations in K+ channel activation/inactivation kinetics.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of the kidney in canine blood pressure control: direct assessment of the closed‐loop gain.
Authors: Persson P B , Ehmke H , Kirchheim H R , Lempinen M , Nafz B
Published: December 2014

1. The feedback control of arterial blood pressure by the kidney in the range of hours was investigated in resting, conscious foxhounds. 2. A servo‐control device (connected to an aortic occlusive cuff implanted above both renal arteries) was used to maintain a constant pressure difference of 20 mmHg between aortic pressure measured proximal (mean arterial blood pressure: MAP) and distal (renal artery pressure: RAP) to the aortic cuff. 3. Protocol 1 (n = 6) served as a 4 h time control without intervention, protocol 2 (n = 6) consisted of three periods: after a control of 20 min duration, the servo‐control device was activated for 180 min; this was followed by a recovery period of 40 min. Protocol 3 (n = 6) was as protocol 2, but during converting‐enzyme inhibition. 4. Servo‐control increased plasma renin activity (PRA) transiently from 0.5 ng angiotensin I (AI) ml‐1 h‐1 to a peak value of 2.4 ng AI ml‐1 h‐1, subsequently both RAP and MAP rose to reach a new steady state. During this increase in RAP, PRA declined to 1.4 ng AI ml‐1 h‐1. 5. On average, the compensation of the pressure decrease sensed by the kidney amounted to 63% of the error signal (closed‐loop gain of 0.63 +/‐ 0.1). 6. Converting‐enzyme inhibition reduced this closed‐loop gain significantly (protocol 2 vs. protocol 3, 0.63 +/‐ 0.1 vs. 0.15 +/‐ 0.1; P < 0.05). 7. It is concluded, that the kidney plays an important role in medium‐term blood pressure regulation, most probably via the renin‐angiotensin system.
Suppression of the slow K+ current by cholinergic agonists in cultured chick cochlear ganglion neurones.
Authors: Yamaguchi K , Ohmori H
Published: December 2014

1. Effects of cholinergic agonists on the cultured chick cochlear ganglion (CG) neurone were examined using the whole‐cell patch‐clamp method. 2. Acetylcholine (ACh, 0.1‐100 microM) and its non‐hydrolysable form, carbamylcholine (CCh, 0.1‐300 microM), suppressed the outward current. The CCh‐sensitive current was activated at membrane potentials more positive than ‐70 mV. 3. The CCh‐sensitive current slowly activated after step depolarization with a time constant from 20 to 150 ms. The activation time constant decreased monotonically with depolarization of the membrane. 4. The reversal potential of CCh‐sensitive current changed as a function of the external K+ concentration (‐79, ‐65 and ‐44 mV in 5, 10 and 25 mM, respectively) and was approximately equal to the potassium equilibrium potential (‐89, ‐71 and ‐48 mV in 5, 10 and 25 mM, respectively). The CCh‐sensitive current is concluded to be K+ selective. 5. The CCh‐sensitive current showed a sigmoid log dose vs. response relationship with an apparent dissociation constant (KD) of 1.4 microM and a Hill coefficient of 1.0. When ACh was applied, an apparent KD of 1.8 microM and a Hill coefficient of 1.0 was measured. 6. The suppression of K+ current by CCh was blocked by atropine (3 microM) and pirenzepine (3 microM), suggesting that the current is mediated by an M1 muscarinic receptor. 7. The CCh suppression of the K+ current was enhanced by GTP‐gamma‐S (0.1 mM), suggesting that a GTP‐binding protein is involved. 8. The CCh suppression of the K+ current was mimicked by protein kinase C activators, 1‐oleoyl‐2‐acetyl‐sn‐glycerol (OAG, 100 microM), phorbol dibutyrate (PDBu, 2 microM) and phorbol 12‐myristate 13‐acetate (PMA, 1 microM). The protein kinase inhibitor, staurosporine (0.2 microM) applied internally blocked the CCh suppression of the K+ current which suggests an involvement of protein kinase C.
Single‐channel study of the cyclic AMP‐regulated chloride current in guinea‐pig ventricular myocytes.
Authors: Ehara T , Matsuura H
Published: December 2014

1. Properties of the cyclic AMP‐regulated Cl‐ channel were studied in guinea‐pig ventricular myocytes with the patch clamp technique. Cell‐attached patch recordings were performed, while the cell was dialysed with a cyclic AMP (0.2‐0.5 mM)‐containing internal solution through a second patch pipette. The latter pipette was also used to monitor the whole‐cell Cl‐ conductance. 2. The whole cell showed a large Cl‐ conductance for 10‐15 min after the beginning of cell dialysis. The activity of single Cl‐ channels began to appear in some of the cell‐attached patches during this time. 3. The channels showed a high open probability (0.69 +/‐ 0.14, mean +/‐ S.D., n = 12) at the time of their appearance, and the open probability did not appreciably increase thereafter, even when the whole‐cell Cl‐ conductance increased further with time. 4. An increase in the number of active channels was observed in some patches with progression of the cell dialysis. In such cases, the newly activated channels also showed a high open probability. 5. The above results are consistent with the hypothesis that the cyclic AMP system makes the ‘latent’ Cl‐ channels available without influencing their own kinetic behaviour. The available channels may intrinsically exhibit a high open probability. 6. Chloride channel currents could also be recorded in the outside‐out patches excised from the cyclic AMP‐loaded cells. The I‐V relation of these currents showed outward rectification under the condition of symmetrical Cl‐ gradients, suggesting that the channel itself or a related structure has the property of rectifying current flow. 7. The channel seemed to have at least one open state and two closed states; the open‐time histograms showed one exponential component with the values of time constant scattering around 1 s, while the closed‐time histograms showed two exponential components with the values of time constant scattering around 0.2 and 1 s. These time constants showed no clear voltage dependence.
Nitric oxide‐related vasodilator responses to parasympathetic stimulation of the submandibular gland in the cat.
Authors: Edwards A V , Garrett J R
Published: December 2014

1. The extent to which parasympathetic vasodilator responses, in the submandibular gland of the cat, depend upon release of nitric oxide related (NO chi) or endothelium‐derived relaxing factor (EDRF) within the gland has been investigated in anesthetized cats given N omega‐nitro‐L‐arginine methyl ester (L‐NAME) which specifically blocks the synthesis of EDRF from arginine. 2. Close intra‐arterial infusions of L‐NAME (> or = 100 mg kg‐1) produced a steady and significant rise in mean aortic pressure together with a steady increase in basal submandibular vascular resistance over the next 20‐30 min, which persisted thereafter. 3. In cats pretreated with propranolol, to block beta‐adrenoceptor‐mediated vasodilatation, salivation and vasodilatation in response to stimulation of the chorda‐lingual nerve were reduced but not abolished by L‐NAME (> or = 100 mg kg‐1, I.A.). Subsequent administration of atropine (> or = 1 mg kg‐1 I.V.) completely suppressed the secretory response and virtually eliminated the vascular response. 4. In cats pretreated with atropine (> or = 1.0 mg kg‐1 I.V.) administration of L‐NAME (> or = 100 mg kg‐1 I.A.) effectively suppressed the vasodilator response to chorda‐lingual stimulation at 2 Hz continuously, or at 20 Hz for 1 s at 10 s intervals. 5. Administration of L‐NAME (> or = 100 mg kg‐1 I.A.) effectively suppressed the submandibular vasodilator response to infusions of VIP (10 and 20 ng I.A.) and significantly reduced, but did not abolish that to acetylcholine (100 ng min‐1 I.A.). 6. These results provide further support for the view that both acetylcholine and vasoactive intestinal polypeptide‐like immunoreactivity (VIP) are released from the postganglionic parasympathetic nerve terminals and produce effects on the blood vessels in submandibular glands of the cat. They also provide evidence for a direct vascular action of acetylcholine, independent of NO chi, but VIP appears to act indirectly via NO chi formation.
Saccade‐vestibulo‐ocular reflex co‐operation and eye‐head uncoupling during orientation to flashed target.
Authors: Ron S , Berthoz A , Gur S
Published: December 2014

1. Eye‐head co‐ordination in the horizontal plane was studied in four human subjects using two successive flashes in the same direction, either increasing in eccentricity (IE), or decreasing in eccentricity (DE). 2. Results showed that for both conditions, head movements preceded eye movements and were typically longer or followed by a slow gaze movement. This slow movement was due to a vestibulo‐ocular reflex gain of less than one. Gaze accuracy was achieved by small head movement adjustments. 3. Gaze movement to an IE stimulus had a staircase pattern, and to a DE stimulus, a pulse‐step pattern or one gaze saccade to the final flash eccentricity. 4. In some cases, however, in response to a DE stimulus, the eye and head movements were directed to different displacements (dissociation); i.e. the head movement started towards the first flash eccentricity with a concomitant eye saccade to the second flash eccentricity. When this occurred, gaze movement did not resemble a pulse‐step pattern. 5. It is suggested that non‐visually orienting gaze is driven mainly by head movement. Eye and head movements can be either tightly coupled or dissociated, depending on the stimulus pattern.
Influence of body position on pressure and airflow generation during hypoxia and hypercapnia in man.
Authors: Xie A , Takasaki Y , Popkin J , Orr D , Bradley T D
Published: December 2014

1. Inspiratory oesophageal pressure and ventilatory responses to hyperoxic, progressive hypercapnic rebreathing (HCVR) and isocapnic, progressive hypoxic rebreathing (HVR) were studied in five normal males in both supine and upright seated positions. 2. No significant differences were found in the ventilatory response to hypercapnia between the supine and upright position. The slopes of the relationship between minute ventilation (VI) and the increase of end tidal PCO2 (delta P(ET), CO2) were 3.27 +/‐ 0.23 and 2.76 +/‐ 0.24 1 min‐1 mmHg‐1 supine and upright, respectively. However, the change in oesophageal pressure from the end expiratory level observed during quiet breathing to that at peak inspiration (delta P(oes), I) in relationship to delta P(ET),CO2 was greater supine than upright (1.23 +/‐ 0.07 versus 0.79 +/‐ 0.11 cmH2O mmHg‐1, P < 0.01). 3. In contrast, during hypoxia‐stimulated breathing the slope of the minute ventilation versus oxyhaemoglobin saturation curve (VI‐Sa,O2) was flatter supine than upright (1.00 +/‐ 0.03 versus 1.75 +/‐ 0.05 l min‐1 (percentage fall in Sa,O2)‐1, P < 0.0001), but delta P(oes), I in relation to Sa,O2 during hypoxic rebreathing was similar supine and upright (0.38 +/‐ 0.03 versus 0.40 +/‐ 0.04 cmH2O (percentage fall in Sa,O2)‐1, respectively. 4. It is concluded that body position does not affect the ventilatory response to progressive hyperoxic hypercapnia but does affect the relationship between delta P(oes), I and delta P(ET),CO2. In contrast, body position affects the ventilatory response to isocapnic progressive hypoxia, but does not affect the relationship between delta P(oes), I and Sa,O2.