bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of electrical rhythmicity in the murine gastrointestinal tract is specifically encoded in the tunica muscularis
Authors: Ward Sean M. , Harney Sarah C. , Bayguinov Julia R. , McLaren Gerald J. , Sanders Kenton M. 
Published: September 2004

Interstitial cells of Cajal (ICCs) have been identified as pacemaker cells in the gastrointestinal (GI) tracts of vertebrates. We have studied the development of ICCs in pacemaker regions and the onset of electrical rhythmicity in the gastric antrum, small bowel and proximal colon of the mouse.
ICCs, as detected by c‐Kit immunofluorescence, were found during embryogenesis in regions of the GI tract that eventually become pacemaker areas. Prior to birth, these cells were organized into well‐structured networks, and by the end of the embryonic period the morphology of ICC networks in pacemaker regions appeared very similar to that observed in adult animals.
Electrical rhythmicity was recorded prior to birth (by E18) in the proximal GI tract (stomach and jejunum), and this activity developed to adult‐like behaviour within a week after birth. In the ileum and proximal colon rhythmicity developed after birth, and adult‐like characteristics were apparent within the first week.
Post‐junctional responses of smooth muscles to neural inputs could be recorded at birth, and stimulation of intrinsic nerves often led to oscillatory activity resembling slow waves for up to several minutes following brief stimuli. Nerve stimulation augmented spontaneous activity in the proximal portions of the GI tract and elicited rhythmic activity temporarily in quiescent tissues of the distal GI tract.
ICCs and rhythmicity developed in an apparently normal manner in tissues isolated at birth and placed in organ culture. These data suggest that the tunica muscularis provides a suitable microenvironment for the development of ICCs and rhythmicity without the need for extrinsic stimuli.
Treatment of small intestinal tissues taken from embryos at E15 with neutralizing c‐Kit antibodies abolished ICC development and the organization of ICCs into networks that typically occurs during the late embryonic period. Treatment of muscles taken from newborn animals with c‐Kit antibodies blocked postnatal development of ICCs, disrupted already established and functional ICC networks, and rendered muscles electrically quiescent.
In summary, ICC networks develop in the pacemaker regions of the murine GI tract before birth. Development and organization of ICCs of the myenteric plexus region into networks precedes the development of electrical rhythmicity. Post‐natal development of electrical rhythmicity is mainly characterized by enhancement of the amplitude and frequency of slow waves. The development of ICCs and electrical rhythmicity persists in vitro. ICCs appear to be necessary for the initiation of electrical rhythmicity. These findings provide further evidence for the pacemaker role of ICCs.
The effects of chronic hypoxia on renal function in the rat
Authors: Neylon Marie , Marshall Janice M. , Johns Edward J. 
Published: September 2004

Studies were performed on rats that had been made chronically hypoxic (CH rats) in a normoxic chamber at 12% O2 for 3–5 weeks. Under Saffan anaesthesia, respiratory and cardiovascular variables, renal haemodynamics and renal function were recorded while the rats spontaneously breathed 12% O2 followed by a switch to air breathing for 20 min. Plasma renin activity was assessed by radioimmunoassay of angiotensin I. Plasma atrial natiruetic peptide (ANP) was indirectly assessed by measurement of cyclic GMP in urine.
When breathing 12% O2, CH rats showed hyperventilation and raised haematocrit (52%) relative to normoxic (N) rats. But arterial pressure (ABP), renal blood flow (RBF), renal vascular conductance (RVC), mean right atrial pressure (mRAtP), urine flow, glomerular filtration rate (GFR) and absolute sodium excretion (UNaV) were comparable to those recorded in N rats breathing air. Urinary cGMP was 40% greater than in N rats, but plasma renin activity was not significantly greater in CH than in N rats.
Air breathing in CH rats induced hypoventilation, a 12% increase in ABP, no change in mRAtP, RBF or GFR, but increases of 75 and 100% in urine flow and UNaV, respectively. Neither urinary cGMP nor plasma renin activity changed. Such increases in urine flow and UNaV were absent when renal perfusion pressure (RPP) was prevented from rising during air breathing by using an occluder on the dorsal aorta.
We propose that by 3–5 weeks of chronic hypoxia renal function was normalized, principally because arterial O2 content was normalized by the increase in haematocrit and because ABP and renal haemodynamics were normalized: acute hypoxia in N rats produces a fall in ABP. We suggest that plasma ANP was raised by the actions of hypoxia or erythropoietin on the atrium, rather than by atrial distension, but suggest that ANP had little direct influence on renal function and tended to limit the influence of the renin–angotensin system. We further propose that the diuresis and natriuresis seen during air breathing were mediated by the increase in RPP; neither plasma ANP nor renin activity change in the immediate short term.
P‐glycoprotein is not a swelling‐activated Cl− channel; possible role as a Cl− channel regulator
Authors: Vanoye Carlos G. , Altenberg Guillermo A. , Reuss Luis 
Published: September 2004

The whole‐cell configuration of the patch‐clamp technique was used to determine if P‐glycoprotein (Pgp) is a swelling‐activated Cl− channel.
Hamster pgp1 cDNA was transfected into a mouse fibroblast cell line resulting in expression of functional Pgp in the plasma membrane. This cell line was obtained without exposure to chemotherapeutic agents.
Swelling‐activated whole‐cell Cl− current (Icl,swell) was elicited by lowering the bath osmolality. Icl,swell, was characterized in detail in the pgp1‐transfected mouse cell line and compared with that of its parental cell line. Expression of Pgp did not modify the magnitude or properties of Icl,swell, except that addition of the anti‐Pgp antibody C219 to the pipette solution inhibited this current by 75% only in the Pgp‐expressing cells.
I
Cl,swell in the mouse Pgp‐expressing cell line was compared with that in a Pgp‐expressing hamster fibroblast cell line. The characteristics of ICl,swell (voltage dependence, blocker sensitivity, anion selectivity sequence, requirement for hydrolysable ATP) in Pgp‐expressing cells were different between the two cell lines. These results suggest that the channel(s) responsible for ICl,swell are different between the two cell lines. In addition, C219 inhibited ICl,swell in both Pgp‐expressing cell lines, even though they seem to express different swelling‐activated Cl− channels.
We conclude that firstly, Pgp is not a swelling‐activated Cl− channel; secondly, it possibly functions as a Cl− channel regulator; and thirdly, ICl,swell is underlined by different Cl− channels in different cells.
Inwardly rectifying, volt age‐dependent and resting potassium currents in rat pancreatic acinar cells in primary culture
Authors: Schmid Andreas , Feick Peter , Schulz Irene 
Published: September 2004

In exocrine pancreatic acinar cells in primary culture an inwardly rectifying, a voltage‐dependent and a permanent resting K+ current were characterized.
Inwardly rectifying K+ currents could be elicited by elevation of the extracellular K+ concentration. The K+ inward currents were almost completely blocked by 5 mm Ba2+, whereas 10 mm TEA+ had only a partial effect.
Depolarizing voltage steps from negative clamp potentials evoked transient activation of a voltage‐dependent K+ current. This voltage‐dependent current could be blocked by 10 mm TEA+ and 1 mm 4‐aminopyridine, but not by 5 mm Ba2+.
Neither the K+ inward rectifier nor the voltage‐dependent K+ conductance produced a significant negative cell potential. Stable membrane potentials (–38.7 ± 2.3mV, n= 38) could only be recorded on cell clusters (≥ 5 cells).
Cell clusters, in contrast to single cells, had a permanent resting K+ conductance in addition to the inward rectifier and the voltage‐dependent current. This resting K+ conductance was not blocked by TEA+, Ba2+, 4‐aminopyridine or by the chromanol 293B.
Cytosolic alkalization by addition of NH4Cl to the bath solution decreased the resting K+ current. In parallel, electrical uncoupling of the cells and breakdown of the resting potential could be observed. The same effects could be produced when the cells were uncoupled by 0.2–1.0 mm n‐octanol. It can be concluded that cell coupling is essential for maintenance of stable resting membrane potentials in pancreatic acinar cells.
Voltage‐gated and inwardly rectifying potassium channels
Authors: Jan Lily Yeh , Jan Yuh Nung 
Published: September 2004

This lecture is dedicated to Max Delbrück and Seymour Benzer. Max Delbrück was our graduate advisor. He introduced us to a variety of biophysical problems, and taught us ways of thinking about these problems by example. Potassium channels was one of the topics included in his journal club in the early seventies; Max also carefully considered the feasibility of purifying potassium channels then. It was in Seymour Benzer's laboratory that we began to look for Drosophila mutants that aÍfect synaptic transmission at the larval neuromuscular junction. Shaker was the first behavioural mutant we tested that gave a robust phenotype, a phenotype that could be mimicked by treating wild‐type preparations with a potassium channel blocker. This mutant fly has led us to our subsequent molecular studies of potassium channels.Since we settled in the University of California, San Francisco, and began to study neural development as well as potassium channels, we have settled into the pattern of each attending meetings and presenting our studies on one of these two areas so as to avoid both being away from home and our children at the same time. In following this pattern, I will be presenting the studies of potassium channels as part of our long‐term collaboration. In this talk I will first briefly take you through the path that led us to the molecular studies of potassium channels and then discuss the diversity and modulation of these potassium channels at the molecular and physiological level.
Plasticity of Na+ Channels in Afferent Neurones Innervating Rat Urinary Bladder Following Spinal Cord Injury
Authors: Yoshimura Naoki , de Groat William C. 
Published: September 2004

Whole‐cell patch‐clamp recordings in combination with axonal tracing techniques were used to investigate the effects of chronic spinal cord injury on the electrical properties of dorsal root ganglion neurones innervating the urinary bladder or colon of the adult rat.
In spinal intact animals, the majority (73–74%) of bladder and colon neurones which were small in size exhibited high‐threshold humped spikes mediated by tetrodotoxin (TTX)‐resistant Na+ channels, whereas large neurones had low‐threshold narrow spikes mediated by TTX‐sensitive Na+ channels.
In chronic spinal transected animals, 60% of bladder afferent neurones exhibited TTX‐sensitive low‐threshold spikes. The average diameter and input capacitance of the cells were significantly larger than those of cells obtained from spinal intact animals.
In bladder afferent neurones from chronic spinal transected rats, the density of TTX‐resistant Na+ currents significantly decreased from 60.5 to 17.9 pA pF−1, whereas that of TTX‐sensitive currents increased from 32.1 to 80.6 pA pF−1.
These changes in action potential and Na+ current characteristics were not detected in colon afferent neurones following spinal cord injury.
The results indicate that spinal cord injury increases bladder afferent neurone excitability by shifting the expression of Na+ channels from a high‐threshold TTX‐resistant type to a low‐threshold TTX‐sensitive type. This change in properties may occur in response to alterations in neurotrophic signals originating in the hypertrophied bladder.
Activation of the Insular Cortex During Dynamic Exercise in Humans
Authors: Williamson J. W. , Nobrega A. C. L. , McColl R. , Mathews D. , Winchester P. , Friberg L. , Mitchell J. H. 
Published: September 2004

The insular cortex has been implicated as a region of cortical cardiovascular control, yet its role during exercise remains undefined. The purpose of the present investigation was to determine whether the insular cortex was activated during volitional dynamic exercise and to evaluate further its role as a site for regulation of autonomic activity.
Eight subjects were studied during voluntary active cycling and passively induced cycling. Additionally, four of the subjects underwent passive movement combined with electrical stimulation of the legs.
Increases in regional cerebral blood flow (rCBF) distribution were determined for each individual using single‐photon emission‐computed tomography (SPECT) co‐registered with magnetic resonance (MR) images to define exact anatomical sites of cerebral activation during each condition.
The rCBF significantly increased in the left insula during active, but not passive cycling. There were no significant changes in rCBF for the right insula. Also, the magnitude of rCBF increase for leg primary motor areas was significantly greater for both active cycling and passive cycling combined with electrical stimulation compared with passive cycling alone.
These findings provide the first evidence of insular activation during dynamic exercise in humans, suggesting that the left insular cortex may serve as a site for cortical regulation of cardiac autonomic (parasympathetic) activity. Additionally, findings during passive cycling with electrical stimulation support the role of leg muscle afferent input towards the full activation of leg motor areas.
Interactions between neuropeptide Y and the adenylate cyclase pathway in rat mesenteric small arteries: role of membrane potential
Authors: Prieto Dolores , Buus Carsten , Mulvany Michael J. , Nilsson Holger 
Published: September 2004

Simultaneous measurements of membrane potential and tension were performed to investigate the intracellular mechanisms of neuropeptide Y (NPY) in rat mesenteric small arteries.
NPY (0.1 μM)depolarized arterial smooth muscle cells from −55 to −47 mV and increased wall tension by 0.22N m−1, representing 11% of the contraction elicited by a high potassium solution. Isoprenaline (1 μM) and acetylcholine (1 μM) evoked hyper polarizations of 11 and 17 mV, resupectively. NPY inhibited the isoprenaline ‐induced effects on membrane potential without affecting those of acetylcholine.
Forskolin evoked sustained concentration‐dependent hyper polarizations of small mesenteric arteries. NPY (0.1 mM) inhibited the resuponses to 1 μM forskolin, but did not alter the stable hyperpolarization elicited by the supecific activator of protein kinase A (PKA) SP‐5,6‐DCl‐cBIMPS (0.1 mm). Forskolin increased the cyclic AMP (cAMP) content of the arteries 21‐fold, and NPY inhibited the forskolin‐evoked increase in cAMP levels by 91 %.
The hyperpolarization produced by 1 μM forskolin was not affected by either charybdotoxin (0.1 μM) or 4‐aminopyridine (0.5mM), but glibenclamide (5 μM) inhibited the hyperpolarization by 70%. Glibenclamide also inhibited the hyperpolarization evoked by SP‐:5,6‐DCl‐cBIMPSuby59%.
Neither depolarization nor contraction caused by NPY were significantly affected by either glibenclamide (5 μM) or nifedipine (1 μM), but they were reduced by gadolinium (10 μM). However, the blocking effect of NPY on forskolin‐elicited hyperpolarization was not affected by gadolinium.
Charybdotoxin (O.1 μM) and 4‐aminopyridine (0.5 mM) strongly enhanced the depolarization and contraction caused by NPY (O.1μM), and nifedipine (1 μM) prevented the enhanced resuponses to NPY in the presence of charybdotoxin.
These findings suggest that NPY acts through at least two different intracellular mechanisms in mesenteric small arteries: a depolarization of arterial smooth muscle which is probably due to activation of non‐selective cation channels, and a marked inhibition of adenylate cyclase activity, which in turn inhibits the hyperpolarization produced by cAMP accumulation in these arteries.
Single channel properties of recombinant GABAA receptors containing γ2 or δ subtypes expressed with α1 and β3 subtypes in mouse L929 Cells
Authors: Fisher Janet L. , Macdonald Robert L. 
Published: September 2004

To determine their contributions to GABAA receptor (GABAR) channel properties, rat γ2L and δ subunits were acutely co‐expressed with α1 and β3 subtypes in mouse L929 fibroblasts to produce α1β3, α1β3δ or α1β3γ2L GABAR isoforms.
With whole‐cell recording, the α1β3 isoform had relatively high sensitivity to GABA (EC50 2.1 μm) and low maximum current amplitude. The α1β1δ isoform had similar sensitivity to GABA (EC50 2.8 μm) and low current amplitude. The α1β3γ2L isoform had lower sensitivity to GABA (EC50 11.6 μm) and higher maximum current amplitude.
The single channel conductance of α1β3 channels was low (13 pS) compared with that of α1α3δ and α1β3γ2L channels (27 pS).
The single channel kinetic properties of the channels also differed. The α1β3γ2L channel exhibited three open states, while the α1β3 and α1β3δ channels exhibited only two open states with mean dwell times similar to those of the two shorter open states of the α1β3γ2L channel. All three channels exhibited at least five closed states. Bursts of α1β3δ channels consisted primarily of only one or two openings, while those of α1β3 channels contained multiple openings. α1β3γ2L channels exhibited burst kinetics typical for native GABARs with several long openings per burst.
These results show that the α1β3 heterodimer formed a GABA‐sensitive channel with complex gating kinetics. Addition of a δ subunit to form the α1β3δ heterotrimer altered the single channel conductance and the kinetic properties of the closed components, but did not affect the GABA sensitivity of the receptor nor the open state kinetics. In contrast, addition of a γ subunit (γ2L subtype) to produce the α1β3γ2L heterotrimer affected the GABA sensitivity, channel conductance and kinetic properties of both open and closed states.
Scorpion Toxin Block of the Early K+ Current (IKf) in Rat Dorsal root Ganglion Neurones
Authors: Matteson Donald R. , Blaustein Mordecai P. 
Published: September 2004

The ability of three structurally homologous scorpion toxins to block voltage‐dependent K+ currents in rat dorsal root ganglion neurones was examined using the patch‐clamp technique.
Neurones with a diameter > 35 μm had two identifiable components of macroscopic K+ current. The outward current during depolarizations had both inactivating and non‐inactivating components, and the tail currents had both a fast component (IKf) with a time constant of about 2.5 ms and a slow component (IKs) with a time constant of about 10 ms.
The functional properties of IKf and IKs differed in several ways: (i)IKf activated over a more negative voltage range than IKf; (ii)IKf partially inactivated during a depolarization to +70 mV, whereas IKs did not inactivate during a 1 s depolarization to +70 mV; (iii)IKf activated more rapidly than IKs;and (iv)α‐dendrotoxin selectively blocked IKf.
Tityustoxin‐Kα (TsTX‐Kα) selectively blocked IKf, with little or no effect on IKs. The block was concentration dependent, with 50% of the current inhibited at a toxin concentration of about 38nM.
TsTX‐Kα block of IKf was completely reversible, but the washout rate was slow. The time constant of recovery from TsTX‐Kα block was about 11 min.
Charybdotoxin (CTX) also selectively blocked IKf in a reversible manner, but was about 10 times less potent than TsTX‐Kα. The CTX washout rate was over 10 times faster than that of TsTX‐Kα; the time constant of recovery was 0.8 min.
Pandinotoxin‐Kα (PiTX‐Kα) also selectively blocked IKf; the IC50 for block of IKf was about 8.1nM. In contrast to the other two toxins, however, PiTX‐Kα was poorly reversible.
The block of IKf produced by CTX was voltage dependent. In the voltage range from ‐10 to +70 mV, the fraction of blocked IKf fell from 91 to 37%. In contrast, both TsTX‐Kα and PiTX‐Kα blocked IKf in a voltage‐independent manner.
The backbone structure and many of the amino acid side‐chains on the presumed docking surfaces of the toxins are identical or conservatively replaced in all three toxins. Thus, some small differences in a few side‐chains that influence electrostatic, hydrophobic/hydrophilic and/or steric interactions probably account for the marked differences in affinities and dissociation rates.
Cation Permeability of a Cloned Rat Epithelial Amiloride‐Sensitive Na+ Channel
Authors: Ismailov Iskander I. , Shlyonsky Vadim Gh. , Alvarez Osvaldo , Benos Dale J. 
Published: September 2004

Conductance of heterotrimeric rat epithelial Na+ channels (α,β,γ‐rENaCs) for Li+ and Na+ in planar lipid bilayers was a non‐linear function of ion concentration, with a maximum of 30.4 ± 2.9 pS and 18.5 ± 1.9 pS at 1 M Li+ and Na+, respectively.
The α,β,γ‐rENaC conductance measured in symmetrical mixtures of Na+–Li+ (1 M) exhibited an anomalous mole fraction dependence, with a minimum at 4:1 Li+ to Na+ molar ratio.
Permeability ratios PK/PNa and PLi/PNa of the channel calculated from the biionic reversal potentials were dependent on ion concentration: PK/PNa was 0.11 ± 0.01, and PLi/PNa was 1.6 ± 0.3 at 50 mm; PK/PNa was 0.04 ± 0.01 and PLi/PNa was 2.5 ± 0.4 at 3 M, but differed from the ratios of single‐channel conductances in symmetrical Li+, Na+ or K+ solutions. The permeability sequence determined by either method was Li+ > Na+ > K+≫ Rb+ > Cs+.
Predictions of a model featuring two binding sites and three energy barriers (2S3B), and allowing double occupancy, developed on the basis of single ion current–voltage relationships, are in agreement with the observed conductance maximum in single ion experiments, conductance minimum in the mole fraction experiments, non‐linearity of the current–voltage curves in biionic experiments, and the concentration dependence of permeability ratios.
Computer simulations using the 2S3B model recreate the ion concentration dependencies of single‐channel conductance observed for the immunopurified bovine renal amiloride‐sensitive Na+ channel, and short‐circuit current in frog skin, thus supporting the hypothesis that ENaCs form a core conduction unit of epithelial Na+ channels.