bluuebunny/crossref_metadata_2025 huggingface dataset:
Relation between Na+‐K+ pump, Na+ activity and force in strophanthidin inotropy in sheep cardiac Purkinje fibres.
Authors: Abete P , Vassalle M
Published: December 2014

1. The effects of different concentrations of strophanthidin on intracellular sodium activity (aiNa), membrane potential and contractile force have been studied in cardiac sheep Purkinje fibres under conditions (overdrive) that stimulate Na+‐K+ pump activity. 2. In fibres driven at 1 Hz, a 5 min overdrive at 2 Hz in the steady state increased force by +74.2%, aiNa by +10.9% and the maximum diastolic potential (Emax) by 3.32 +/‐ 0.52 mV. 3. During the recovery from overdrive (the fibres being driven again at 1 Hz), both contractile force and aiNa transiently undershot the control value by ‐10.5 and ‐3.7%, respectively. When the fibres were quiescent during the recovery from overdrive, no aiNa undershoot was present. 4. During overdrive, force and aiNa were closely correlated when plotted either on linear (correlation coefficient, R = 0.98) or logarithmic (R = 0.98) co‐ordinates. 5. A low concentration of strophanthidin (0.01 microM) decreased force (‐31.7%) and aiNa (‐7.2%): overdrive increased force and Emax more and aiNa less than in the absence of strophanthidin. During the recovery, the undershoot in force (‐12.9%) and aiNa (‐5.4%) was larger and longer than in the absence of strophanthidin. 6. An intermediate concentration of strophanthidin (0.05 microM) increased force (+43.5%) and aiNa (+6.4%): overdrive increased force and aiNa as usual, but during the recovery the force remained above the value prior to overdrive and there was no aiNa undershoot. 7. A high concentration of strophanthidin (0.1 microM) increased force (+91.4%) and aiNa (+11.7%): overdrive further increased force and aiNa more than in control but there was no increase in Emax. During the recovery, both force and aiNa remained well above the values prior to overdrive. 8. Force and aiNa were closely correlated whether aiNa decreased in 0.01 microM‐strophanthidin (R = 0.99 both on linear and logarithmic co‐ordinates) or increased in 0.05‐microM‐ (R = 1.00 on both co‐ordinates) and in 0.1 microM‐ (R = 0.98 and 0.99, respectively) strophanthidin. The two parameters were well correlated also during overdrive in the three strophanthidin solutions. However, the slope of the relation was less steep in the low‐ than in the higher‐strophanthidin solutions. 9. For a 1 mM change in aiNa, force decreased less in the low‐ than it increased in the intermediate‐strophanthidin solution. Also, in low‐strophanthidin solution, at the end of overdrive the aNao/aNai ratio was similar to that in Tyrode solution but force was well above control (+73.2%).(ABSTRACT TRUNCATED AT 400 WORDS)
Prolonged noxious mechanical stimulation of the rat's tail: responses and encoding properties of dorsal horn neurones.
Authors: Cervero F , Handwerker H O , Laird J M
Published: December 2014

1. Single‐unit electrical activity has been recorded from dorsal horn neurones in the sacral (S1‐S2) segments of the spinal cord of barbiturate‐anaesthetized rats. Fifty‐two neurones responding to a manually applied pinch of their receptive fields in the tail were selected. They were subsequently tested for their responses to four successive 2 min pinches at noxious intensities delivered by a feed‐back‐controlled mechanical device. 2. Neurones were tested with both innocuous (i.e. brushing and stroking) and noxious (i.e. pinching, pin‐prick, and in some cases heating about 45 degrees C) stimulation of their cutaneous receptive fields. Three of the tested cells were driven exclusively by innocuous skin stimulation (mechanoreceptive or class 1), thirty‐six were driven by both innocuous and noxious skin stimulation (multireceptive or class 2) and thirteen were driven exclusively by noxious skin stimulation (nocireceptive or class 3). 3. All of the multireceptive and nocireceptive neurones responded to the 2 min noxious pinch with an initial phasic discharge followed by sustained firing that showed little evidence of adaptation throughout the stimulus period. The three mechanoreceptive neurones responded to the 2 min noxious pinch with a short discharge at the stimulus onset, but were silent for the remainder of the stimulus period. 4. Thirty‐one cells were tested with successive 2 min pinches of 4, 6 and 8 N (and in some cases, a further 4 N pinch) applied at 10 min intervals. Different encoding properties were observed during the sustained part of the neuronal response according to: (i) the afferent fibre input characteristics of the cell; (ii) whether or not the tail had received a test series of pinches earlier in the same experiment. 5. None of the multireceptive cells with only an A‐fibre afferent input encoded the stimulus strength. However, the multireceptive cells with both an A‐ and a C‐fibre afferent input and all nocireceptive cells did encode the stimulus strength, providing that no previous noxious test stimuli had been applied to the tail. The encoding nocireceptive neurones had in general a steeper stimulus‐response curve than the encoding multireceptive neurones, though the two groups overlapped to some extent. 6. Three encoding cells (two multireceptive and one nocireceptive) were tested with a second series of pinches (4, 6, 8 and 4 N), 40 min subsequent to the initial test series. These cells did not encode this second test series, but were more excitable, producing a greater response to a given test force.(ABSTRACT TRUNCATED AT 400 WORDS)
Transmission of burst responses through slices of rat cerebral cortex.
Authors: Boakes R J , Burns B D , Webb A C
Published: December 2014

1. Slices of rat's forebrain, 400 micron thick, have been cut and maintained in a bath perfused with warm oxygenated Krebs solution. Records were made with extracellular micropipettes of the neural responses to local stimulation of the cortex itself or the underlying white matter. 2. Single stimuli at either of these sites could produce an all‐or‐nothing burst response among nearby neurones. This response usually lasted 0.2‐0.5 s during which repetitively discharging cortical units could be recorded at all cortical depths. 3. This burst response was transmitted from the stimulated point across the cortex in all directions with a velocity of roughly 0.1 m s‐1. 4. Complete recovery of excitability among neurones generating the burst response took about 10 s. 5. Removal of Ca2+ from the perfusate prevented transmission of this response, as did a high concentration of Mg2+ or 160 mg/100 ml of ethanol. 6. Propagation of the burst response was not dependent upon the integrity of the underlying white matter; it required only that any 20% of the cortical thickness was intact and undamaged. 7. In coronal sections of brain the response could be transmitted from one hemisphere to the other provided that the corpus callosum was intact.
An analysis of the depolarization produced in guinea‐pig hippocampus by cholinergic receptor stimulation.
Authors: Benson D M , Blitzer R D , Landau E M
Published: December 2014

1. The effects of carbachol on hippocampal pyramidal neurones were studied in tissue slices in vitro with intracellular microelectrodes, employing current clamp and voltage clamp methods. 2. The calcium‐dependent potassium current, IAHP, and the voltage‐dependent potassium current, IM, were both reversibly blocked by the application of carbachol (5‐10 microM). 3. Carbachol (1‐10 microM) induced a steady inward current under circumstances in which both IAHP and IM were inactive. This inward current was sometimes difficult to reverse upon carbachol wash‐out, an effect possibly related to receptor desensitization. 4. The depolarizing effect of carbachol was reversed by 0.1 microM‐atropine, and exhibited an apparent dissociation coefficient of 1.2 microM for carbachol and 18 nM for pirenzepine, indicating that it is mediated by activation of an M1 muscarinic receptor. 5. The depolarizing effect or inward current induced by carbachol was completely blocked by the potassium channel blockers caesium, tetraethylammonium and barium. 6. The slope of the current‐voltage (I‐V) plots in carbachol was reduced in the majority of cells, and crossed the control I‐V plots at a negative membrane potential. The reversal potentials in carbachol shifted in a positive direction when bathing potassium concentration was increased. 7. In a number of cells, the I‐V curves in carbachol were parallel to or converged positively with the control I‐V curves. 8. The effects of carbachol were compared to those of serotonin, which increases a ‘pure’ potassium conductance. Serotonin (10 microM) produced an increase in the slope of the I‐V curve, with a reversal potential sensitive to changes in bathing potassium concentration. The carbachol reversal potential values were negative to those of serotonin at 5 and 10 mM‐potassium. The equilibrium potentials for carbachol and serotonin were equal at 25 mM‐potassium. 9. The negative values of the reversal potential at 5 and 10 mM‐potassium and the occurrence of non‐crossing I‐V characteristics in carbachol could be explained by postulating a second effect of carbachol: namely, a non‐specific conductance increase in the dendrites. 10. It is concluded that carbachol depolarizes pyramidal cells in the hippocampus by blocking a voltage‐insensitive potassium leak channel and does so by activating M1 muscarinic receptors. In addition, carbachol may also activate a second conductance in the dendrites, which could account for the anomalous I‐V characteristics sometimes seen in response to carbachol in these cells.
Membrane ionic mechanisms activated by noradrenaline in cells isolated from the rabbit portal vein.
Authors: Byrne N G , Large W A
Published: December 2014

1. Membrane currents were recorded in cells freshly dispersed from the rabbit portal vein with patch pipette techniques in the whole‐cell configuration of recording. In potassium‐containing solutions at a holding potential of ‐50 mV noradrenaline usually evoked an inward current and enhanced greatly the outward current evoked by depolarizing voltage steps. 2. The ionic mechanism of the inward current was investigated in potassium‐free solutions in which the inward current elicited by noradrenaline was produced by an increase in membrane conductance. 3. In the first series of experiments NaCl was the main salt in the patch pipette solution (representing the intracellular milieu) and the ionic composition of the bathing solution was altered. In these conditions the reversal potential of the noradrenaline‐induced current was close to the chloride equilibrium potential (ECl). 4. When sodium glutamate was the major salt in the pipette solution the reversal potential of the noradrenaline‐evoked current was influenced by the cation rather than the anion gradient. 5. With 89 mM‐BaCl2 in the external solution (and sodium glutamate in the pipette) noradrenaline produced a membrane current with a reversal potential which was much more positive than ECl or ENa. These results indicate that noradrenaline opens a chloride‐selective channel and a cation channel which is permeable to monovalent and divalent cations. 6. Bath application of 10 mM‐caffeine evoked a membrane current with a reversal potential close to ECl with either NaCl or sodium glutamate in the pipette. This is interpreted to mean that the increase in membrane chloride conductance can occur as a consequence of a rise in intracellular calcium concentration. It is less evident that the cation channel is calcium activated.
The dynamics of the cat retinal Y cell subunit.
Authors: Victor J D
Published: December 2014

1. The dynamics of the subunit mechanism of individual cat Y retinal ganglion cells are investigated. In order to isolate the response of the non‐linear subunit mechanism, the visual stimuli were sine gratings of a spatial frequency sufficiently high so that contrast reversal of the grating elicited no fundamental response in any spatial phase. For study of the non‐linear subunit mechanism, the contrast of the spatial spine grating was varied in time by a temporal modulation signal, consisting of either a square wave or a sum of sinusoids. 2. The responses of twenty‐three Y ganglion cells (sixteen on‐centre, seven off‐centre) to these two stimulus types were measured at a range of contrasts. Responses to the sum‐of‐sinusoids signal were characterized by the second‐order frequency kernel. The overall size of the second‐order frequency kernel was approximately proportional to contrast. The deviation from proportionality suggested a power‐law scaling, with a power in the range 0.8‐0.9. 3. Square‐wave responses, as characterized by the post‐stimulus histogram, demonstrated identical responses at both reversals of the grating. A similar contrast dependence was observed in the overall size of the square‐wave responses. 4. In order to attempt to predict the square‐wave responses from the sum‐of‐sinusoids responses, the second‐order frequency kernel measured at each contrast level was fitted with a lumped linear‐static non‐linear‐linear model. In eighteen of twenty‐three cells (eleven on‐centre, seven off‐centre), this model provided an adequate description of the response to the sum‐of‐sinusoids stimulus. In these cells, the linear‐static non‐linear‐linear model accurately reproduced the square‐wave response. 5. In the remaining five ganglion cells (all on‐centre), the second‐order frequency kernel could not be fitted by a linear‐static non‐linear‐linear model. This diversity of dynamical properties among Y cells was not apparent from the responses of these Y cells to the square‐wave temporal stimulus. 6. In the eighteen Y ganglion cells that were fitted well with the linear‐static non‐linear‐linear model, substantial variation of the dynamical parameters was found. However, there were systematic differences between the dynamics of the typical on‐centre and off‐centre ganglion cells. These differences relate to both linear stages of the model, and are not merely consequences of the lower firing rate of the off‐centre cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Cortical contrast gain control in human spatial vision.
Authors: Bobak P , Bodis‐Wollner I , Marx M S
Published: December 2014

1. We evaluated human visual cortical contrast gain using visual evoked potential (VEP) measurements. The steady‐state VEP was elicited by 7.5 Hz contrast modulation of a 6 cycles/deg sinusoidal grating. The stimulus may be regarded as the sum of a steady grating (C) and a counterphase grating of the same spatial frequency (delta C). The counterphase grating is modulated sinusoidally in time. 2. The VEP was measured to combinations of different modulation contrasts (delta C) and different mean levels of grating contrast (C) which produced stimuli with contrast modulation depths (delta C/C) ranging from 0.0625 to 1.0 (‘on‐off’). 3. The VEP signals were Fourier analysed and the amplitude and phase of the first (7.5 Hz) and second (15 Hz) harmonic frequency components were examined. The monocular VEP to a contrast‐modulated grating contains significant first and second harmonic frequency components. 4. The amplitude and phase of the monocular VEP was plotted as a function of delta C for each mean level of contrast explored. The amplitudes of both the first and second harmonic frequency components grow with increasing delta C. However, the slope of each function depends on the mean contrast (C): with higher levels of C, the slope of the function is more shallow. Furthermore, at each level of C the amplitude of the first harmonic frequency saturates at a lower delta C than does the second harmonic frequency component. VEP amplitude is therefore not determined by the absolute contrast change (delta C) alone. The VEP phase of the first harmonic frequency shows less dependence on either modulation or on mean contrast; the phase of the second harmonic frequency component is strongly dependent on mean contrast (C) but not on delta C. 5. When the second harmonic amplitude component of the VEP response (R) is expressed as Ractual/Rmax, where Rmax is the response to C = delta C (i.e. ‘on‐off’), all second harmonic VEP functions can be well fitted with a power function. This is not the case for the function of the first harmonic amplitude data. 6. A dichoptic VEP was obtained by presenting the steady and counterphase gratings to opposite eyes. The dichoptic VEP, in distinction to the monocular VEP, contains only a second harmonic frequency component. The amplitude of the second harmonic frequency component grows with increasing delta C, similar to the function seen for the monocular VEP.(ABSTRACT TRUNCATED AT 400 WORDS)
Muscarinic control of the hyperpolarization‐activated current (if) in rabbit sino‐atrial node myocytes.
Authors: DiFrancesco D , Tromba C
Published: December 2014

1. The mechanism by which acetylcholine (ACh), by stimulation of muscarinic receptors, acts to inhibit activation of the hyperpolarization‐activated ‘pacemaker’ current, if was investigated in isolated rabbit sino‐atrial (SA) node myocytes. 2. Intracellular loading with GTP gamma S, a non‐hydrolysable analogue of GTP, did not impair the ACh action on if, but made it irreversible. On the other hand, the ACh action on if disappeared after a few minutes of cell loading with GDP beta S, a GDP analogue known to bind to G‐proteins and prevent their receptor‐stimulated action. Furthermore, incubation of cells in a solution containing pertussis toxin (PTX) led to abolition of the if response to ACh. These results indicate that the inhibitory effect of ACh on if is mediated by G‐proteins activated by muscarinic receptors. 3. Intracellular loading with phosphodiesterase (PDE) increased the rate of if current run‐down, but did not abolish the inhibitory action of ACh on if. 4. Extracellular perfusion with isobutylmethylxanthine (IBMX), a PDE inhibitor, increased if activation by shifting the current activation range to more positive voltages, as inferred by a three‐pulse protocol analysis; in the presence of IBMX, the inhibition of if by ACh was not abolished. 5. The ACh‐induced if depression persisted also in cells loaded with cyclic GMP. In these cells, as in those loaded with PDE, the if run‐down was fast. 6. Oxotremorine, a muscarinic agonist coupled to adenylate cyclase but not to phosphoinositide turnover in cardiac cells, simulated ACh in its inhibitory action on if. The above results rule against the ACh action being mediated by PDE or by phosphoinositide turnover. 7. To investigate the possible involvement of cyclic AMP as a second messenger in the ACh action on if, we loaded cells with cyclic AMP and IBMX; under these conditions the action of ACh disappeared within a few minutes of whole‐cell recording. 8. In cells where the slow inward Ca2+ current (isi) was measured together with if, ACh was seen to depress both currents. 9. In cells superfused with forskolin, the if amplitude on stepping to the half‐activation voltage range was enhanced as a consequence of a depolarizing shift of the activation curve; ACh was not effective on if following stimulation by forskolin, but strongly depressed in the same cell the if current stimulated to a similar degree by isoprenaline.(ABSTRACT TRUNCATED AT 400 WORDS)
Glutamate receptors of ganglion cells in the rabbit retina: evidence for glutamate as a bipolar cell transmitter.
Authors: Massey S C , Miller R F
Published: December 2014

1. Intracellular and extracellular recordings were obtained from ganglion cells in the rabbit retina. The effects of glutamate analogues and antagonists were studied using a perfusion method for drug application. 2. Kainate (KA) excited all ganglion cells directly and caused a large increase in firing rate. N‐Methyl‐DL‐aspartate (NMDLA) also excited ganglion cells but it was less potent and caused burst firing. 3. Quisqualate (QQ) and (RS)‐2‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionic acid (AMPA) excited many ganglion cells and were approximately as potent as KA. Less frequently, QQ and AMPA had inhibitory effects possibly due to polysynaptic action. 4. General glutamate antagonists such as cis‐2,3‐piperidine dicarboxylic acid (PDA) and kynurenic acid blocked the light input to all ganglion cells. PDA and kynurenic acid blocked the effects of KA and NMDLA, but not carbachol, indicating that they act as glutamate antagonists in the rabbit retina. Kynurenic acid did not block the excitatory action of QQ, even though light responses were abolished. 5. Amacrine cells were depolarized by KA or QQ and less potently by NMDLA. Their light‐evoked responses were blocked by PDA. 6. We conclude that the light input to ganglion cells in the rabbit retina is predominantly mediated by KA receptors. This is consistent with the idea that ‘on’ and ‘off’ bipolar cells are excitatory and release glutamate.
The modulation of the ionic selectivity of the light‐sensitive current in isolated rods of the tiger salamander.
Authors: Cervetto L , Menini A , Rispoli G , Torre V
Published: December 2014

1. By using the method of Hodgkin, McNaughton & Nunn (1985) for rapidly changing the extracellular medium, we analysed the effect of the organic compound IBMX (3‐isobutyl‐1‐methylxanthine) on the movement of divalent cations through the light‐sensitive channels of isolated retinal rods of the tiger salamander. 2. When the rod is treated with 0.5 mM‐IBMX it is possible to observe photocurrents larger than 50 pA carried by Ba2+, Sr2+, Ca2+, Mg2+ and Mn2+. Under these conditions Ca2+, Mg2+ and Mn2+ carry photocurrents of similar amplitude, while Ba2+ and Sr2+ usually carry larger photocurrents. 3. The movement of Mn2+ through the light‐sensitive channel, which is hardly detected under normal conditions, can also be observed after treating the rod for a few seconds with a solution containing 35 mM[Na+]o and 10(‐7) M[Ca2+]o. Under these conditions the photocurrent carried by Mn2+ is fully saturated in the presence of 1 mM‐extracellular Mn2+. 4. When the rod is pre‐treated with an extracellular solution containing 0.5 mM‐IBMX the maximal photocurrent which can be carried by 10 mM [Ca2+]o increases from about 10 pA to approximately 200 pA. In these conditions the half‐activation of the Ca2+ current is between 1 and 10 mM, that is 20‐50 times higher than in normal conditions (Menini, Rispoli & Torre, 1988). 5. When the rod is pre‐treated with an extracellular solution containing 0.5 mM‐IBMX the half‐activation of the photocurrent which can be carried by Mg2+, Ba2+ and Sr2+ is equivalent to or greater than 10 mM. In the absence of pre‐treatment with IBMX the half‐activation of the photocurrent carried by Mg2+, Ba2+ and Sr2+ is less than 5 mM. 6. We conclude that the light‐sensitive channel can exist in at least two distinct open states. The selectivity of the channel in the first open state is as described in a previous paper (Menini et al. 1988). Mn2+, which is hardly permeable through the light‐sensitive channel in the first open state, can move through the light‐sensitive channel in the second open state. Ca2+, Mg2+, Ba2+ and Sr2+ permeate more freely through the light‐sensitive channel in the second open state, probably because the electrostatic interactions between these ions and the channel are less strong.
Spontaneous release of multiquantal miniature excitatory junction potentials induced by a Drosophila mutant.
Authors: Ikeda K , Koenig J H
Published: December 2014

1. Intracellular recordings were made from muscle fibre No. 6 of the dorsal longitudinal flight muscle (DLM) of Drosophila melanogaster in both wild‐type flies and the temperature‐sensitive paralytic mutant, shibirets‐1 (shi). 2. Continuous recordings of the miniature excitatory junction potentials (MEJPs) in this fibre were made as the temperature was changed from 19 to 29 degrees C, and back to 19 degrees C. In shi flies, synapses become depleted of vesicles at 29 degrees C due to a temperature‐dependent blockage in the recycling process, while transmitter release proceeds normally. When the temperature is lowered to 19 degrees C, recycling is allowed to proceed and recovery of the full complement of synaptic vesicles gradually occurs in about 20 min. 3. It was observed that the MEJP amplitude distribution in shi flies was unimodal at 19 degrees C prior to heating (as was wild‐type), but during recovery from 8 min exposure to 29 degrees C became multimodal, with peaks at roughly integral multiples of the original peak prior to heating. This effect was never seen in wild‐type flies. 4. Also, during recovery, the MEJP did not occur randomly, but rather occurred in a clustered fashion. 5. It is concluded that during recovery from depletion in shi neuromuscular junctions, a condition exists which causes the synchronization of spontaneous release, causing multiquantal MEJPs or clustering of MEJPs, depending on the degree of synchronization. 6. The possible role of Ca2+ in this phenomenon is discussed.
Measurement of myoglobin diffusivity in the myoplasm of frog skeletal muscle fibres.
Authors: Baylor S M , Pape P C
Published: December 2014

1. Experiments were carried out on intact, single skeletal muscle fibres from frog in order to estimate the apparent diffusion constant of myoglobin (denoted DAPP) in the myoplasm of living muscle cells. An optical technique was employed to measure myoglobin concentration along the fibre axis following injection of metmyoglobin (denoted metMb) at a point source. The concentration profiles were fitted by the one‐dimensional diffusion equation to give estimates of DAPP. The method relied on the fact that myoglobin is normally absent from these frog fibres, thus permitting resolution of the myoglobin‐related absorbance above the intrinsic absorbance of the fibre. 2. One complication in the method was that metMb became significantly reduced to oxymyoglobin (denoted MbO2) during the elapsed time before measurement of the concentration profile. The rate of reduction was evaluated by fitting myoglobin‐related absorbance spectra, measured at different times following injection of metMb, with in vitro absorbance spectra of metMb and MbO2. Results from four experiments indicated that reduction could be described by a first‐order, irreversible reaction having an average rate constant of 0.0164 min‐1 (22 degrees C). The effect of reduction on the fitting of DAPP was taken into account. 3. DAPP was determined under three fibre conditions: (1) long sarcomere spacing (3.6‐3.8 microns) at 16 degrees C, (2) long sarcomere spacing at 22 degrees C, and (3) normal sarcomere spacing (2.4‐2.7 microns) at 22 degrees C. The average values for DAPP under these conditions were: (1) 0.12 (n = 5); (2) 0.17 (n = 5); and (3) 0.15 (n = 7) x 10(‐6) cm2 s‐1. The average value at 22 degrees C, 0.16 x 10(‐6) cm2 s‐1, is about 4 times smaller than values for myoglobin diffusivity at 20 degrees C commonly assumed in models of facilitated transport of oxygen by myoglobin. 4. In order to test the possibility that the unexpectedly low value of DAPP found in intact fibres might be due to the binding of myoglobin to relatively immobile sites in myoplasm, experiments were carried out in a cut‐fibre preparation using a technique described by Maylie, Irving, Sizto & Chandler (1987 b) for determining the diffusion constants and degree of myoplasmic binding of absorbance dyes. Values for DAPP and the factor (denoted 1 + beta) by which the total myoglobin concentration exceeded the free myoglobin concentration were obtained by fitting the absorbance data by solutions of the one‐dimensional diffusion equation.(ABSTRACT TRUNCATED AT 400 WORDS)
Two inhibitory postsynaptic potentials, and GABAA and GABAB receptor‐mediated responses in neocortex of rat and cat.
Authors: Connors B W , Malenka R C , Silva L R
Published: December 2014

1. Pyramidal neurones from layers II and III of the rat primary somatosensory cortex and cat primary visual cortex were studied in vitro. Inhibitory postsynaptic potentials (IPSPs) and responses to exogenously applied gamma‐aminobutyric acid (GABA) and its analogue baclofen were characterized. The results from rats and cats were very similar. 2. Single electrical stimuli to deep cortical layers evoked a sequence of PSPs in the resting neurone: (a) an initial, brief excitation (EPSP), (b) a short‐latency, fast inhibition (the f‐IPSP) and (c) a long‐latency, more prolonged inhibition (the l‐IPSP). The f‐IPSP was accompanied by a large conductance increase (about 70‐90 nS) and reversed polarity at ‐75 mV; the l‐IPSP displayed a relatively small conductance increase (about 10‐20 nS) and reversed at greater than ‐90 mV. 3. Focal application of GABA near the soma evoked a triphasic response when measured near the threshold voltage for action potentials: (a) the GABAhf (hyperpolarizing, fast) phase was very brief and was generated by a large conductance increase with a reversal potential of ‐78 mV, (b) the GABAd (depolarizing) phase also had a high conductance but reversed at ‐51 mV, (c) the GABAhl (hyperpolarizing, long‐lasting) phase had a relatively low conductance and reversed at ‐70 mV. The GABAhf response was specifically localized to the soma, whereas the apical or basilar dendrites generated predominantly GABAd responses. 4. Baclofen, a selective GABAB receptor agonist, caused a small (about 2 mV), slow hyperpolarization of the resting potential, which reversed at ‐90 mV. Saturating baclofen doses increased membrane conductance by a maximum of about 12 nS. Baclofen depressed the amplitude and conductance of PSPs; when baclofen was focally applied near the soma. IPSPs were selectively depressed. 5. The GABAA receptor antagonists bicuculline methiodide or picrotoxin (10 microM) greatly depressed f‐IPSPs, but either enhanced or did not affect l‐IPSPs. Concomitantly, GABAhf and GABAd responses were antagonized, leaving a more prominent GABAhl response that reversed polarity at a more negative level of ‐87 mV. Baclofen responses were unaffected by bicuculline and picrotoxin. Extracellular barium abolished the baclofen response, and shifted the reversal potentials of the GABAd and GABAhl responses in the positive direction; the GABAhf response was unaffected. 6. Both focal GABA and f‐IPSPs strongly depressed the intrinsic excitability of pyramidal neurones. Each greatly increased spike threshold and abolished or vastly reduced the capacity of the cells to fire repetitively during intense stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
The absence of cardiovascular and respiratory responses to changes in right ventricular pressure in anaesthetized dogs.
Authors: Crisp A J , Hainsworth R , Tutt S M
Published: December 2014

1. This study was undertaken to determine whether physiological changes in pressure localized to the right ventricle result in reflex cardiovascular or respiratory responses. 2. Right ventricular systolic pressure was changed using a preparation in which right atrial and carotid sinus pressures were held constant. The pulmonary and hence the systemic circulation were perfused at constant flow. Vascular resistance and respiratory activity were assessed from the systemic arterial pressure and the phrenic electroneurogram. 3. Changes in right ventricular systolic pressure did not result in any consistent changes in heart rate, systemic arterial blood pressure or phrenic nerve activity. 4. Expected responses occurred to changes in the stimuli to carotid baroreceptors and chemoreceptors, distension of pulmonary arterial baroreceptors, and injections of veratridine into the left ventricle and pulmonary circulation. This suggests that the absence of responses to right ventricular distension was unlikely to have been due to damage to nervous pathways. 5. These results indicate that it is unlikely that there are reflexes arising from the right ventricle which have a major role in cardiovascular or respiratory control.
Phosphorus nuclear magnetic resonance studies on the effect of duration of contraction in bull‐frog skeletal muscles.
Authors: Kawano Y , Tanokura M , Yamada K
Published: December 2014

1. Contraction and recovery of bull‐frog skeletal muscles were studied using 31P nuclear magnetic resonance (NMR), with a time resolution of 16 s, at 4 degrees C. The muscles were stimulated tetanically for various periods (0.2‐10 s) at a sarcomere length of 2.4 microns. Changes in the concentrations of inorganic phosphate (Pi), phosphocreatine (PCr) and other metabolites were studied for repeated cycles of contraction and recovery. 2. In resting muscles, bathed in a solution gassed with 95% O2 and 5% CO2, the concentration of Pi was 1.15 +/‐ 0.21 mmol kg‐1 wet weight (mean +/‐ one S.D., n = 12), that of ATP was 3.32 +/‐ 0.15 mmol kg‐1 (mean +/‐ one S.D., n = 12) and that of sugar phosphates was less than 0.5 mmol kg‐1. The intracellular pH (pHi) was 7.22 +/‐ 0.01 (mean +/‐ one S.D., n = 12). These results are averages for fibres which probably have different values. 3. On stimulating the muscles pHi shifted in the alkaline direction and subsequently recovered. The extent of the alkaline shift was linearly related to the contraction duration (0.2‐10 s) with a rate of 0.01 pH unit s‐1. 4. The increase in Pi with stimulus duration was biphasic, consisting of an early burst, 0.38 +/‐ 0.10 mmol kg‐1 (+/‐ 1 S.D., n = 5), complete within about 0.2‐0.5 s, followed by a slower steady‐state increase. The steady‐state rate of Pi increase was 0.33 +/‐ 0.02 mmol kg‐1 s‐1 (+/‐ 1 S.D., n = 5) in agreement with the results of previous studies involving chemical analyses. 5. The time course of Pi recovery was well described by a single exponential. Intensities of ATP, sugar phosphates and the peaks in the phosphodiester region did not change during a 2 s tetanus. 6. The amount of PCr hydrolysed (‐delta PCr), associated with contractions of various durations, coincided well with Pi increase (delta Pi). This was found during the whole recovery period except for the initial few minutes following relaxation when ‐delta PCr was significantly smaller than delta Pi. The difference was 0.35 +/‐ 0.03 mmol kg‐1 (mean +/‐ 1 S.D., n = 3) immediately after a 2 s tetanus. 7. In contractions of 2 s or longer, the extent of the temporal separation between delta Pi and ‐delta PCr was almost the same, but in contractions of less than 2 s it was significantly reduced.(ABSTRACT TRUNCATED AT 400 WORDS)
Prolonged depolarization in turtle cones evoked by current injection and stimulation of the receptive field surround.
Authors: Burkhardt D A , Gottesman J , Thoreson W B
Published: December 2014

1. Responses evoked by stimulation of the receptive field surround were recorded intracellularly from cone photoreceptors in the retina of the turtle (Pseudemys scripta elegans). 2. A distinctive depolarizing response was evoked by flashing an annulus of light while steadily illuminating the centre of the receptive field. The response, here called ‘the prolonged depolarization’, was found in 67% of a sample of 125 cones and could reach some 20 mV in amplitude. 3. The prolonged depolarization is characterized by a set of properties which include: the capacity to persist up to 17 s after the flash, a stereotypical waveform, a long period of temporal facilitation, a very narrow dynamic range, and a long refractory period (30‐45 s). 4. Depolarizing current pulses (0.01‐0.1 nA) evoke a prolonged depolarization which is similar to and functionally interchangeable with that evoked by light. The prolonged depolarization is thus apparently generated by a voltage‐sensitive mechanism intrinsic to the cone. 5. Brief depolarizing spikes were recorded in a small fraction of cones. The spikes appear to be dissociable from the prolonged depolarization although both might arise for similar regenerative mechanisms. 6. The prolonged depolarization is typically preceded by a graded, stimulus‐locked depolarization which can also be recorded in isolation by flashing annuli of low intensity. The graded depolarization is probably a manifestation of the depolarizing influence arising from synaptic feed‐back from horizontal cells first described by Baylor, Fuortes & O'Bryan (1971). 7. It is suggested that the graded depolarization triggers the prolonged depolarization and that complex responses arise from the interaction of these disparate components.
Characteristics of acidic, basic and neutral amino acid transport in the perfused rat hindlimb.
Authors: Hundal H S , Rennie M J , Watt P W
Published: December 2014

1. We have employed a paired‐tracer isotope dilution technique in a perfused rat hindlimb preparation to obtain information on the kinetics of transport across the sarcolemmal membranes of acidic, neutral and basic amino acids. 2. We have defined the characteristics of the saturable transport of amino acids normally regarded as paradigm substrates for the A, ASC, L, y+(basic) and the dicarboxylic amino acid transport systems. Their maximal transport capacities (Vmax, nmol min‐1 (g muscle)‐1 and substrate concentrations for half‐maximal transport (Km, mM) of representative amino acid substrates are as follows: 2‐aminoisobutyrate (AIB), Vmax = 15 +/‐ 7, Km = 1.26 +/‐ 0.6; alanine, Vmax = 332 +/‐ 53, Km = 3.9 +/‐ 0.9; serine, Vmax = 410 +/‐ 61, Km 3.4 +/‐ 0.5; leucine, Vmax = 2800 +/‐ 420, Km = 20 +/‐ 2; lysine, Vmax = 136 +/‐ 46, Km = 2.1 +/‐ 1.3; glutamate, Vmax = 86 +/‐ 6, Km = 1.05 +/‐ 0.05; proline, Vmax = 196 +/‐ 48, Km = 4.1 +/‐ 0.6. 3. Glycine uptake was faster than expected on the basis of diffusion but was not saturable and showed uptake that could be best described by a first‐order rate constant of 0.07 +/‐ 0.003 min‐1. 4. We have attempted to discriminate kinetically between possible routes of entry for an amino acid on the basis of competitive and non‐competitive interaction between substrates potentially sharing common routes. On this basis, the major routes of alanine entry appear to be via the ASC and L systems with the A system playing a quantitatively minor role. Glutamate and aspartate appear to be transported exclusively by a dicarboxylate amino acid carrier. The branched‐chain amino acids (BCAA) and the aromatic amino acid, phenylalanine, are almost equivalent substrates for an L‐like system. 5. Insulin had no detectable effect on the uptake of paradigm substrates for ASC, L, y+, the dicarboxylic amino acid or glycine transport systems. 6. Transport of serine and lysine was Na+ dependent. Lysine transport apparently occurred with a stoichiometry of 2 Na+: 1 lysine. With the exception of alanine, whose transport was partially Na+ dependent, all other amino acids examined in the present study were transported in a Na+‐independent manner.
Dynamics of coronary adjustment to a change in heart rate in the anaesthetized goat.
Authors: Dankelman J , Spaan J A , Stassen H G , Vergroesen I
Published: December 2014

1. We have previously shown that steady‐state coronary flow during auto‐regulation and metabolic rate changes is predicted by a mathematically expressed theory which assigns control of coronary vascular resistance to tissue PO2. Our present purpose was to test the applicability of this theory to the non‐steady state as exemplified by a sudden step change in heart rate. 2. The theory predicted that the response time of change of resistance in these circumstances would be slower with constant‐flow perfusion of the coronary bed than with constant‐pressure perfusion, and that with constant‐pressure perfusion only, the rate of adaption of resistance would be dependent on the level of pressure used. 3. These predictions were tested in open‐chest goats with cannulation of the left main coronary artery and perfusion with alternately constant pressure or constant flow. Sudden step changes in heart rate were induced by pacing to induce rapid transients in myocardial metabolic rate. 4. The half‐time of subsequent change in perfusion pressure‐flow ratio, which in the dynamical state is not equal to resistance, was 15.7 +/‐ 0.4 s (mean +/‐ S.E.M.), which was statistically shorter than for constant flow (22.2 +/‐ 0.5 s, P less than 0.001). 5. The half‐time of subsequent change in perfusion pressure‐flow ratio with constant‐pressure perfusion was 14.4 +/‐ 0.6 s at low pressure and 17.0 +/‐ 0.6 s at high pressure (P less than 0.001). 6. The results differed from those predicted by the theory, in that the changes described above were preceded by a rapid (5 s) step change in pressure‐flow ratio, up with an increase in heart rate and down with a decrease in heart rate. We postulated that this was a mechanical effect due to greater compression of the coronary microvasculature with more frequent contractions. 7. To test this hypothesis, we measured changes in coronary blood volume by integrating the difference between arterial inflow and venous outflow. These experiments showed a decrease in coronary blood volume with heart rate increase and vice versa. 8. Abolition of autoregulation and metabolic regulation was achieved with maximum vasodilatation of the coronary bed with adenosine. A sudden switch in heart rate then produced the initial step change in pressure‐flow ratio, but not the subsequent adaptation over 13‐25 s. This confirmed that the former effect is attributable to a passive mechanical mechanism.
Effect of extracellular adenosine triphosphate on electrical properties of subconfluent Madin‐Darby canine kidney cells.
Authors: Lang A J , Paulmichl M
Published: December 2014

1. The present study has been performed to test for an influence of extracellular ATP on the potential differences across the cell membrane (PD) in subconfluent MDCK cells utilizing conventional microelectrodes. 2. In the absence of ATP, the mean measured PD was ‐47.5 +/‐ 0.3 mV (+/‐ S.E.M., n = 320). Application of 10 mumol/l ATP leads to rapid (less than 2 s) hyperpolarization of the cell membrane by ‐18.5 +/‐ 0.4 mV (n = 221), reduction of input resistance by 14 +/‐ 1 M omega (n = 106) and increase of the sensitivity of PD to alterations of extracellular potassium. 3. The concentration needed for half‐maximal effect (K1/2) of ATP is approximately 0.5 mumol/l. ATP‐gamma‐S (K1/2 approximately 0.4 mumol/l) aand ADP (K1/2 approximately 0.9 similarly effective, whereas up to 1 mmol/l AMP or adenosine does not significantly alter PD. Application of 10 mumol/l theophylline, 1 mumol/l phentolamine and 10 mumol/l indomethacin does not blunt the hyperpolarizing effect of ATP. 4. The ATP‐induced hyperpolarization is completely abolished in the presence of 1 mmol/l quinidine but only incompletely by 0.1 mmol/l quinidine or 1 mmol/l barium. In calcium‐free extracellular fluid (1 mmol/l EDTA added) PD is 18.5 +/‐ 1.7 mV (n = 18). With reduced extracellular calcium, the hyperpolarizing effect of ATP is blunted (‐12.3 +/‐ 1.6 mV, n = 18) and only transient. 5. In conclusion, ATP hyperpolarizes MDCK cells by increasing the potassium conductance. The activation of potassium channels requires calcium.
Adenosine 5'‐triphosphate modulates membrane potassium conductance in guinea‐pig myenteric neurones.
Authors: Katayama Y , Morita K
Published: December 2014

1. Intracellular recordings were made from myenteric neurones isolated from the guinea‐pig small intestine to study actions of adenosine 5'‐triphosphate (ATP). ATP was applied by superfusion (10 nM‐100 microM) or pressure ejection from ATP‐containing glass pipettes. 2. Myenteric neurones have been classified into two groups: type I/S neurones and type II/AH neurones. ATP produced a membrane hyperpolarization in 80% of AH neurones and a membrane depolarization in 90% of S neurones in a dose‐dependent manner. Adenosine caused responses similar to those induced by ATP in both AH and S neurones, but was less effective than ATP. 3. The ATP‐induced hyperpolarization was associated with a fall in input resistance, but the ATP‐induced depolarization was accompanied by an increase in input resistance. Both responses reversed in polarity near the potassium equilibrium potential (‐84 to ‐87 mV) and the reversal potential varied with extracellular potassium concentration, as predicted by the Nernst equation. These results indicate that the hyperpolarization is due to an increase, while the depolarization is due to a decrease in potassium conductance. 4. Both the hyperpolarization and the depolarization induced by ATP persisted in calcium‐free solution containing 1.2 mM‐magnesium, but were markedly reduced or abolished in calcium‐free solutions containing 3.7‐10 mM‐magnesium and by 1 mM‐nickel or cobalt. Both responses to ATP persisted in tetraethylammonium (1‐10 mM) or tetrodotoxin (1‐3 microM)‐containing solutions. 5. Quinine and quinidine (1‐100 microM) reversibly depressed both the ATP‐induced responses. Caffeine (100 microM), theophylline (100 microM) and 3‐isobutyl‐1‐methylxanthine (1‐10 microM) did not significantly affect the ATP‐induced depolarization but did reversibly depress the ATP‐induced hyperpolarization. 6. These results suggest that the ATP‐induced hyperpolarization may be due to activation, and the ATP‐induced depolarization to inactivation, of a calcium‐sensitive potassium conductance.
Rubidium and sodium permeability of the ATP‐sensitive K+ channel in single rat pancreatic beta‐cells.
Authors: Ashcroft F M , Kakei M , Kelly R P
Published: December 2014

1. The patch‐clamp method has been used to study the selectivity of single ATP‐sensitive potassium channels in excised membrane patches from dissociated rat pancreatic beta‐cells. 2. In symmetrical K+ concentrations the current‐voltage relation of this channel showed slight inward rectification. The K+ permeability coefficient was 1.05 x 10(‐13) cm3/s ([K+]o = 140 mM; 20 degrees C) in the inside‐out patch and somewhat smaller when measured under the same conditions in the outside‐out configuration (0.86 x 10(‐13) cm3/s). 3. When intracellular Rb+ replaced K+, inward K+ currents were unaffected but the outward currents carried by Rb+ were substantially smaller. The extent of the reduction in the outward currents depended on the internal Rb+/K+ ratio and increased as [Rb+]i was raised. Both inward and outward Rb+ currents were blocked by 1 mM‐ATP. No currents were measurable in symmetrical 140 mM‐Rb+ solutions. 4. With 140 mM [K+]o and 140 mM [Rb+]i the single‐channel current‐voltage relation reversed at +8 mV and the potential at which the variance of the ATP‐sensitive current was least was shifted by 6 mV to more positive potentials. These data suggest a PRb/PK ratio of around 0.7. 5. Outward Rb+ currents were reduced at all potentials in inside‐out patches exposed to 107 mM‐Rb+ solution intracellularly and 5 mM‐K+ externally. 6. Partial replacement of external K+ with Rb+ substantially reduced the inward currents recorded from outside‐out patches and also decreased outward K+ currents. 7. In outside‐out patches, the addition of 1 mM‐Rb+ to the external solution produced a block of inward K+ currents that initially increased and then decreased again with hyperpolarization. This suggests that the Rb+ block of K+ currents is voltage dependent and that Rb+ acts as a permeant blocker of K+ currents. 8. The sodium permeability of the channel, relative to that of potassium, was 0.39 for internal Na+ and 0.007 for external Na+ ions. 9. We conclude that Rb+ serves as an acceptable tracer for K+ in efflux studies when changes in K+ flux through ATP‐sensitive K+ channels are of interest but that the magnitude of such fluxes will be considerably underestimated.