bluuebunny/crossref_metadata_2025_split huggingface dataset:
Potassium channels activated in the endothelium‐dependent hyperpolarization in guinea‐pig coronary artery
Authors: Nishiyama Makoto , Hashitani Hikaru , Fukuta Hiroyasu , Yamamoto Yoshimichi , Suzuki Hikaru 
Published: September 2004

Properties of the endothelium‐dependent hyperpolarization evoked by acetylcholine (ACh) in smooth muscle of the guinea‐pig coronary artery were investigated using conventional microelectrode techniques.
ACh hyperpolarized the membrane in an endothelium‐dependent manner. The hyperpolarization comprised two components: an initial and a slow hyperpolarization. The former appeared during application of ACh, while the latter occurred after withdrawal of ACh.
Indomethacin and diclofenac, inhibitors of the enzyme cyclo‐oxygenase, blocked only the slow hyperpolarization, indicating that this potential was produced by endothelial prostanoids.
Clotrimazole and SKF 525a, known inhibitors of the enzyme cytochrome P450, inhibited both the initial and the slow hyperpolarizations, suggesting that these chemicals acted as non‐selective inhibitors of arachidonic acid metabolism. Inhibition of the lipoxygenase pathway of arachidonic acid metabolism by nordihydroguaiaretic acid had no effect on either component of the hyperpolarization.
The slow hyperpolarization was inhibited by 4‐aminopyridine (4‐AP; 10−4‐10−3 M) and glibenclamide (10−6 M). The initial hyperpolarization was greatly inhibited by charybdotoxin (CTX; 5 × 10−8 M) and partially inhibited by apamin (10−7 M), but was not inhibited by glibenclamide (10−5 M). Ba2+ (10−4 M) depolarized the membrane and increased the amplitude of both components of the ACh‐induced hyperpolarization.
Hyperpolarizations produced by Y‐26763, a K+ channel opener, were inhibited by glibenclamide, but not by 4‐AP.
The results indicate that the slow hyperpolarization is produced by endothelial prostanoids through activation of 4‐AP‐sensitive K+ channels (possibly delayed rectifier type). The initial hyperpolarization is produced mainly through activation of CTX‐sensitive K+ channels (possibly Ca2+‐sensitive type).
Regulated anion secretion in cultured epithelia from Sertoli cells of immature rats
Authors: Ko W. H. , Chan H. C. , Chew S. B. , Wong P. Y. D. 
Published: September 2004

Cultured epithelia of Sertoli cells from prepubertal rats were grown on Matrigel‐coated millipore filters for short‐circuit current (Isc) measurements. Under basal conditions, these epithelia exhibited a ‘zero’ transepithelial potential difference, a ‘zero’ short‐circuit current and a transepithelial resistance of 60 Ω cm2.
Forskolin (100 μm) and 8‐(4‐chlorophenylthio)‐cAMP (cpt‐cAMP) (100 μm) added to the apical side stimulated the Isc (forskolin, peak ΔIsc= 1.32 ± 0.16 μA cm−1; cpt‐cAMP, peak ΔIsc= 0.88 ± 0.16 μA cm−2).
ATP (100 μm) added apically elicited a Isc response (peak ΔIsc= 6.45 ± 0.28 μA cm−2) which was similar in magnitude to that of 1 μm thapsigargin (peak ΔIsc= 6.09 ± 0.44 μA cm−2). The potency of the responses to other nucleotides: UTP ≥ ATP > ADP >> AMP = adenosine indicates the involvement of a mixture of P2Y receptors.
Removal of extracellular Cl− and HCO3− reduced the Isc response to ATP by 70 % and 40 %, respectively. Removal of K+ had no effect, whereas removal of Na+ attenuated the Isc response.
The response to ATP was insensitive to agents known to block anion secretion (except apical diphenylamine‐2‐carboxylate (DPC) and DIDS). The resistance to perturbation by pharmacological agents may be a unique property of the seminiferous epithelium.
Whole‐cell current recordings in cultured rat Sertoli cells demonstrated a DIDS‐sensitive outwardly rectifying Cl− conductance with activating and inactivating characteristics at depolarizing and hyperpolarizing voltages, respectively.
The stimulation of electrogenic ion transport by ATP may be part of a complex mechanism regulating fluid secretion by the testis. Cultured Sertoli cell epithelia are shown to provide a useful model to investigate transepithelial transport in the seminiferous epithelium.
The buffer barrier hypothesis, [Ca2+]i homogeneity, and sarcoplasmic reticulum function in swine carotid artery
Authors: Rembold Christopher M. , Chen Xiao‐Liang 
Published: September 2004

The goal of this study was to evaluate the buffer barrier hypothesis in an intact arterial smooth muscle. Specifically, we investigated the interrelationships between intracellular [Ca2+] ([Ca2+]i) homogeneity and sarcoplasmic reticulum function in swine carotid artery.
We measured focal changes in [Ca2+]i by exploiting the different characteristics of several [Ca2+]i indicators: (1) aequorin, which can detect focal increases in [Ca2+]i such as those that occur in the subplasmalemmal region ([Ca2+]pm); (2) fura‐2, which is primarily a measure of mean cytoplasmic [Ca2+] ([Ca2+]c); and (3) force, which reflects increases in [Ca2+] near the contractile apparatus. We then estimated the relative degree of [Ca2+]i homogeneity with the aequorin/fura‐2 ratio. Finally, we inhibited sarcoplasmic reticulum Ca2+ pumping with cyclopiazonic acid (CPA), an inhibitor of the sarco(endo)plasmic reticulum Ca2+‐ATPase (SERCA).
We found that, after Ca2+ depletion, the sarcoplasmic reticulum could be partially reloaded with Ca2+ by manipulations that increased the aequorin signal relatively more than the fura‐2 signal. Complete reloading required large increases in the fura‐2 signal. These data suggest that increases in [Ca2+]pm (as measured with aequorin) can partially reload the sarcoplasmic reticulum, but complete reloading required increases in [Ca2+]c (as measured with fura‐2). Reloading could be partially inhibited by 10 μM CPA, indicating that SERCA function was important for reloading.
In unstimulated arteries, 10 μM CPA increased the fura‐2 signal without altering the aequorin signal, thereby decreasing the aequorin/fura‐2 ratio. Removal of extracellular Ca2+ without CPA also reduced the aequorin/fura‐2 ratio. These data suggest that resting cells have a [Ca2+] gradient with [Ca2+]pm > [Ca2+]c; this gradient is maintained by SERCA function.
CPA slowed the decline in the fura‐2 signal observed when histamine stimulation was removed. This result is consistent with the concept of vectorial Ca2+ efflux in which Ca2+ pumping by SERCA reduces [Ca2+]c after stimulation.
Ca2+ depletion by prior treatment with 100 μM histamine and CPA transiently attenuated subsequent histamine‐induced aequorin and fura‐2 transients. The effect on contraction was smaller: a delay in contraction of approximately 10 s. These data suggest that histamine‐induced Ca2+ release has at least a small role in the initial phase of contraction; however, other contractile mechanisms appear to be able to compensate for loss of Ca2+ release with only modest changes in contraction kinetics.
These data suggest that there is a complex interrelationship between smooth muscle sarcoplasmic reticulum function and [Ca2+] in at least two cytoplasmic compartments. [Ca2+]pm and [Ca2+]c can differentially regulate sarcoplasmic reticulum Ca2+ filling; and sarcoplasmic reticulum function regulates [Ca2+]pm and [Ca2+]c.
The dynamics of synchronized neurotransmitter release determined from compound spontaneous IPSCs in rat dentate granule neurones in vitro
Authors: Williams Stephen R. , Buhl Eberhard H. , Mody Istvan 
Published: September 2004

The properties of GABAA receptor‐mediated spontaneous IPSCs generated in hippocampal dentate granule neurones were analysed using whole‐cell voltage‐clamp techniques in order to explore the functional consequences of the low number (6‐12) and close proximity of synaptic contacts made by single GABAergic interneurones.
Spontaneous IPSCs (sIPSCs) occurred with a frequency of 14.0 ± 9.1 Hz (n= 31) and revealed a multi‐modal positively skewed amplitude distribution (39.0 ± 19.8 pA, median values).
The variance of 10–90 % rise times and decay kinetics between IPSCs decreased with increasing peak amplitude. Larger amplitude events had significantly faster rise times, consistent with their site of generation being proximal to the soma. The decay kinetics of sIPSCs did not significantly change with amplitude.
Large amplitude sIPSCs occurred singularly or in discrete bursts, repeated regularly at low frequency. The rising phase of such sIPSCs were multi‐phasic, composed of clear step‐like inflections that were not a product of noise. The variability between the rising phase of individual sIPSCs was quantified by calculating their standard deviation, which produced fast rising (0.22 ± 0.05 ms time to peak, n= 16) functions with half‐widths of 0.38 ± 0.10 ms, which declined to plateaux.
Computer simulations demonstrated that IPSCs with properties similar to those recorded experimentally could be generated by the linear summation of groups of temporally dispersed component events. Standard deviation functions of the rising phase of simulated IPSCs accurately described distributions of the temporal dispersion of unitary components.
The GABA uptake inhibitor (R)‐N‐[4,4‐bis(3‐methyl‐2‐thienyl)but‐3‐enl‐yl] nipecotic acid (tiagabine) (10 μM, n= 12) significantly prolonged the decay of mIPSCs (6.5 ± 0.8 to 8.7 ± 1.0 ms, median values) and sIPSCs (6.2 ± 0.4 to 7.3 ± 1.2 ms, median values), but failed to alter the frequency of occurrence, 10–90 % rise times or peak amplitude of events. The application of flurazepam (30 μM, n= 7; 50 μM, n= 4) prolonged the decay of sIPSCs regardless of their amplitude.
These data indicate that sIPSCs are formed by the summation of unitary components that occur asynchronously and that GABA released from multiple sites has independent postsynaptic actions.
Type I and II models of diabetes produce different modifications of K+ currents in rat heart: role of insulin
Authors: Shimoni Y. , Ewart H. S. , Severson D. 
Published: September 2004

Several K+ currents were measured and compared in enzymatically dispersed ventricular myocytes from control and diabetic rats.
Diabetic conditions were established either with a single intravenous injection of streptozotocin (STZ, 100 mg kg−1; 6‐14 days duration) or by feeding with a fructose‐enriched diet for 4‐10 weeks. Both groups became hyperglycaemic, with the former having decreased and the latter having elevated levels of plasma insulin. These conditions therefore mimic type I (insulin‐dependent) and type II (non‐insulin‐dependent) diabetes mellitus, respectively.
As reported previously, a Ca2+‐independent transient outward K+ current, It, was attenuated in the type I model. This was not observed in the type II model. The two models differed greatly in the changes observed in a quasi‐steady‐state K+ current denoted Iss. In the STZ model Iss was substantially attenuated, whereas in the fructose‐fed model it was augmented. In both models, the background inwardly rectifying current, IK1, was unchanged. Concomitantly, there was a substantial prolongation of the action potential in the STZ model but not in the fructose‐fed model.
Incubation of control myocytes with insulin (100 nM) for 5‐9 h caused a significant augmentation of Iss, with no effect on It or on IK1. Incubation of myocytes from STZ‐diabetic rats with insulin reversed the attenuation of It, but not of Iss.
The effect of insulin was not blocked by wortmannin, an inhibitor of phosphatidylinositol 3‐kinase. However, inhibition of the mitogen‐activated protein kinase pathway with PD98059 prevented restoration of It. Insulin action on It may therefore involve changes in transcription or expression of channel proteins, rather than changes in cellular metabolism.
Sarcolemmal mechanisms for pHi recovery from alkalosis in the guinea‐pig ventricular myocyte
Authors: Leem Chae‐Hun , Vaughan‐Jones Richard D. 
Published: September 2004

The mechanism of pHi recovery from an intracellular alkali load (induced by acetate prepulse or by reduction/removal of ambient PCO2) was investigated using intracellular SNARF fluorescence in the guinea‐pig ventricular myocyte.
In Hepes buffer (pHo 7.40), pHi recovery was inhibited by removal of extracellular Cl−, but not by removal of Na+o or elevation of K+o. Recovery was unaffected by the stilbene drug DIDS (4,4‐diisothiocyanatostilbene‐disulphonic acid), but was slowed dose dependently by the stilbene drug DBDS (dibenzamidostilbene‐disulphonic acid).
In 5 % CO2/HCO3− buffer (pHo 7.40), pHi recovery was faster than in Hepes buffer. It consisted of an initial rapid recovery phase followed by a slow phase. Much of the rapid phase has been attributed to CO2‐dependent buffering. The slow phase was inhibited completely by Cl− removal but not by Na+o removal or K+o elevation.
At a test pHi of 7.30 in CO2/HCO3− buffer, the slow phase was inhibited 70 % by DIDS. The mean DIDS‐inhibitable acid influx was equivalent in magnitude to the HCO3−‐stimulated acid influx. Similarly, the DIDS‐insensitive influx was equivalent to that estimated in Hepes buffer.
We conclude that two independent sarcolemmal acid‐loading carriers are stimulated by a rise of pHi and account for the slow phase of recovery from an alkali load. The results are consistent with activation of a DIDS‐sensitive Cl−‐HCO3− anion exchanger (AE) to produce HCO3− efflux, and a DIDS‐insensitive Cl−‐OH− exchanger (CHE) to produce OH− efflux. H+‐Cl− co‐influx as the alternative configuration for CHE is not, however, excluded.
The dual acid‐loading system (AE plus CHE), previously shown to be activated by a fall of extracellular pH, is thus activated by a rise of intracellular pH. Activity of the dual‐loading system is therefore controlled by pH on both sides of the cardiac sarcolemma.
Components of after‐hyperpolarization in magnocellular neurones of the rat supraoptic nucleus in vitro
Authors: Greffrath Wolfgang , Martin Erich , Reuss Stefan , Boehmer Gerd 
Published: September 2004

The pharmacological sensitivity of hyperpolarizing components of spike train after‐potentials was examined in sixty‐one magnocellular neurones of the rat supraoptic nucleus using intracellular recording techniques in a brain slice preparation.
In 26 % of all neurones a slow after‐hyperpolarization (AHP) was observed in addition to a fast AHP. In 31 % of all neurones a depolarizing after‐potential (DAP) was observed.
The fast AHP was blocked by apamin whereas the slow AHP was blocked by charybdotoxin (ChTX). The DAP was enhanced by ChTX or a DAP was unmasked if not present during the control period.
Low concentrations of TEA (0.15–1.5 mm) induced effects on the slow AHP and the DAP essentially resembling those of ChTX. The same was true for the effects of CoCl2 (1 mm).
Spike train after‐potentials were not affected by either iberiotoxin (IbTX), a selective high‐conductance potassium (BK) channel antagonist, or margatoxin (MgTX), a Kv1.3 α‐subunit antagonist.
Kv1.3 α‐subunit immunohistochemistry revealed that these units are not expressed in the somato‐dendritic region of supraoptic neurones.
The effects of ChTX, IbTX, MgTX, TEA, CoCl2 and CdCl2 on spike train after‐potentials are interpreted in terms of an induction of the slow AHP by the activation of calcium‐dependent potassium channels of intermediate single channel conductance (IK channels).
The results suggest that at least the majority of supraoptic magnocellular neurones share the capability of generating both a slow AHP and a DAP. The slow AHP may act to control the expression of the DAP, thus regulating the excitability of magnocellular neurones. The interaction of the slow AHP and the DAP may be important for the control of phasic discharge.
Age‐dependent changes in myosin composition correlate with enhanced economy of contraction in guinea‐pig hearts
Authors: van der Velden J. , Moorman A. F. M. , Stienen G. J. M. 
Published: September 2004

The composition of myosin heavy chains (MHCs) was investigated in young (1‐ to 8‐week‐old) and mature (9‐ to 26‐week‐old) guinea‐pigs using two monoclonal antibodies directed specifically against α‐MHC and β‐MHC. In addition, maximum force and the rate of ATP consumption during isometric contraction were measured in chemically skinned trabeculae taken from the same hearts.
An age‐dependent shift in the MHC composition was found. The α‐MHC fraction decreased from 0.17 ± 0.02 (mean ± s.e.m.; n= 24) in young to 0.04 ± 0.01 (n= 43) in mature hearts. This shift was correlated with a decrease in tension cost (i.e. ATP consumption per second per trabecula volume/force per cross‐sectional area) from 4.1 ± 0.2 mmol kN−1 m−1 s−1 (n= 23) in young to 2.5 ± 0.1 mmol kN−1 m−1 s−1 (n= 57) in mature hearts.
From the results it follows that the slow β‐MHC isoform, which predominates in hearts of mature guinea‐pigs, is about 5 times more economical than the fast α‐MHC isoform. Calcium sensitivity of force and ATP consumption decreased with age, but stabilized within a few weeks after birth. The pronounced dependence of cardiac energetics on MHC composition should be taken into account in long‐term studies of cardiac overload.
Intracellular calcium clearance in Purkinje cell somata from rat cerebellar slices
Authors: Fierro Leonardo , DiPolo Reinaldo , Llano Isabel 
Published: September 2004

The mechanisms governing the return of intracellular calcium (Ca2+i) to baseline levels following depolarization‐evoked [Ca2+]i rises were investigated in Purkinje cell somata using tight‐seal whole‐cell recordings and fura‐2 microfluorometry, for peak [Ca2+]i ranging from 50 nM to 2 μM.
Ca2+i decay was well fitted by a double exponential with time constants of 0.6 and 3 s. Both time constants were independent of peak [Ca2+]i but the contribution of the faster component increased with [Ca2+]i.
Thapsigargin (10 μM) and cyclopiazonic acid (50 μM) prolonged Ca2+i decay indicating that sarco‐endoplasmic reticulum Ca2+ (SERCA) pumps contribute to Purkinje cell Ca2+i clearance.
A modest participation in clearance was found for the plasma membrane Ca2+ (PMCA) pumps using 5,6‐succinimidyl carboxyeosin (40 μM).
The Na+‐Ca2+ exchanger also contributed to the clearance process, since replacement of extracellular Na+ by Li+ slowed Ca2+i decay.
Carbonyl cyanide m‐chlorophenylhydrazone (CCCP, 2 μM) and rotenone (10 μM) increased [Ca2+]i and elicited large inward currents at −60 mV. Both effects were also obtained with CCCP in the absence of external Ca2+, suggesting that mitochondrial Ca2+ uptake uncouplers release Ca2+ from intracellular stores and may alter the membrane permeability to Ca2+. These effects were irreversible and impeded tests on the role of mitochondria in Ca2+i clearance.
The relative contribution of the clearance systems characterized in this study varied as a function of [Ca2+]i. At 0.5 μM Ca2+i, SERCA pumps, PMCA pumps and the Na+‐Ca2+ exchanger contribute equally to removal and account for 78 % of the process. Only 45 % of the removal at 2 μM Ca2+i can be explained by these systems. In this high [Ca2+]i range the major contribution is that of SERCA pumps (21 %) and of the Na+‐Ca2+ exchanger (18 %), whereas the contribution of PMCA pumps is only 6 %.
Changes in the maximum speed of shortening of frog muscle fibres early in a tetanic contraction and during relaxation
Authors: Josephson R. K. , Edman K. A. P. 
Published: September 2004

Isotonic shortening velocities at very light loads were examined in single fibres of the anterior tibialis muscle of the frog, Rana temporaria, using load‐clamp recording and slack tests (temperature, 1‐3 °C; initial sarcomere length, 2.25 μm).
Shortening velocities at very light loads (force‐clamp recording) were found to be higher early in the rise of a tetanic contraction than during the plateau of the contraction. The upper limit of the load at which there was elevated shortening velocity early in the contraction was 1.5‐5.4 % of the maximum tetanic tension (Fo) depending on the particular fibre.
The maximum shortening velocity determined using the slack test method (Vo) was as much as 30 % greater early in a contraction than at the tetanic plateau. Vo was elevated above the plateau level up to about 30 ms after the end of the latent period, which is equivalent to the time required for the force in an isometric contraction to rise to about 30 % of Fo. Vo is depressed below the plateau value during relaxation at the cessation of stimulation.
Simulation studies show that the cross‐bridge model of Huxley (1957) predicts the maximum shortening velocity to be greater early in a contraction, when new actin binding sites are becoming activated and new cross‐bridge connections are being formed rapidly, than during steady‐state contraction. The elevated shortening velocity in the model is a consequence of new cross‐bridges being formed in the pulling configuration, and there being a delay before the newly added bridges are dragged beyond their equilibrium position so they begin to retard shortening. The model also predicts that maximum shortening velocity should be depressed below the plateau level during early relaxation as cross‐bridge binding sites are rapidly removed from the active population.
A leu‐enkephalin depresses transmission from muscle and skin non‐nociceptors to first‐order feline spinal neurones
Authors: Jankowska E. , Schomburg E. D. 
Published: September 2004

The effects of an opioid (D‐Ser‐Leu‐enkephalin‐Thr; DSLET) were tested on synaptic actions of non‐nociceptive afferents: group I and II muscle afferents and low‐threshold skin afferents. They were tested on population EPSPs (field potentials) evoked in the dorsal horn and the intermediate zone of mid‐lumbar segments, and on monosynaptically evoked responses of single interneurones at the same locations. DSLET was applied locally (ionophoretically) at locations at which the field potentials were maximal and close to the selected neurones.
DSLET potently depressed transmission from group II muscle afferents and from low‐threshold skin afferents. Transmission to neurones located in the dorsal horn or in the intermediate zone was depressed to a similar extent. The depression was readily antagonized by naloxone. Transmission from group I a or I b muscle afferents to neurones located in the intermediate zone was not affected, or was facilitated by DSLET.
The results show that DSLET has similar depressive actions on spinal neurones to monoamines, but its actions are more widespread. Like monoamines it affects transmission from nociceptors and group II muscle afferents, but in addition it gates transmission from low‐threshold cutaneous afferents. Furthermore its effects do not appear to be restricted to interneurones at particular locations since it depressed responses of dorsal horn interneurones (gated by serotonin) as well as intermediate zone interneurones (gated by noradrenaline).
Brain‐derived neurotrophic factor is required for normal development of the central respiratory rhythm in mice
Authors: Balkowiec Agnieszka , Katz David M. 
Published: September 2004

Molecular mechanisms underlying maturation of the central respiratory rhythm are largely unknown. Previously, we found that brain‐derived neurotrophic factor (BDNF) is required for expression of normal breathing behaviour in newborn mice, raising the possibility that maturation of central respiratory output is dependent on BDNF.
Respiratory activity was recorded in vitro from cervical ventral roots (C1 or C4) using the isolated brainstem‐spinal cord preparation from postnatal day (P) 0.5–2.0 and P4.5 wild‐type mice and mice lacking functional bdnf alleles.
Loss of one or both bdnf alleles resulted in an approximately 50 % depression of central respiratory frequency compared with wild‐type controls. In addition, respiratory cycle length variability was 214 % higher in bdnf null (bdnf−/−) animals compared with controls at P4.5. In contrast, respiratory burst duration was unaffected by bdnf gene mutation.
These derangements of central respiratory rhythm paralleled the ventilatory depression and irregular breathing characteristic of bdnf mutants in vivo, indicating that central deficits can largely account for the abnormalities in resting ventilation produced by genetic loss of BDNF. BDNF is thus the first growth factor identified that is required for normal development of the central respiratory rhythm, including the stabilization of central respiratory output that occurs after birth.