bluuebunny/crossref_metadata_2025 huggingface dataset:
Muscarinic suppression of Ca2+ current in smooth muscle cells of the guinea‐pig urinary bladder
Authors: Yoshino M , Yabu H
Published: December 2014

The suppressive action of carbachol (CCh) on the Ca2+ current (ICa) in smooth muscle cells of the guinea‐pig urinary bladder was investigated using the whole‐cell patch clamp technique. Bath application of 10 microM CCh reduced the amplitude of ICa by 92 +/− 3.8% (n = 9). Adding 1 microM atropine to the bath completely blocked the action of CCh, indicating that the suppressive action of CCh on ICa is mediated by the activation of muscarinic receptors. Intracellular perfusion of the non‐hydrolysable GTP analogue, guanosine 5'–O‐(3‐thiotriphosphate) (GTP gamma S; 200 microM) mimicked the effects of CCh. Sustained suppression of ICa was observed when GTP gamma S was present in the cytoplasm. Intracellular perfusion of inositol 1,4,5‐trisphosphate (InsP 3; 20 microM) also suppressed ICa; its effect was not sustained but transient. The protein kinase C activator, phorbol 12,13‐dibutyrate (PDBu), however, could not mimic the effects of CCh on ICa. When intracellular Ca2+ was strongly buffered by the Ca2+ chelator EGTA (20 mM) in the patch pipette, the sustained suppression of ICa was abolished. Inclusion of 3 mg/ml heparin, a blocker of InsP3‐induced Ca2+ release, in the patch pipette reduced the degree of sustained ICa suppression by 43.2 +/− 1.9% (n = 7). Adding thapsigargin (TG), a sarcoplasmic reticulum Ca2+‐ATPase inhibitor, to a wash solution reduced the recovery of ICa by about 50%, suggesting that approximately half of the ICa suppression induced by CCh is due to Ca2+ release from TG‐sensitive internal Ca2+ stores. From these results it appears that CCh suppresses ICa via two independent mechanisms: (1) Ca(2+)‐mediated inactivation of the Ca2+ channel, which is caused by Ca2+ release from InsP3‐ and TG‐sensitive internal stores, and (2) a GTP‐binding protein‐mediated mechanism, which requires intracellular Ca2+.
Intestinal calcium transport in mole‐rats (Cryptomys damarensis and Heterocephalus glaber) is independent of both genomic and non‐genomic vitamin D mediation
Authors: Pitcher T , Buffenstein R
Published: December 2014

The role of vitamin D in mineral uptake in the gastrointestinal tract (GIT) of mole‐rats (Heterocephalus glaber and Cryptomys damarensis; family Bathyergidae), animals with a naturally impoverished vitamin D status, was investigated. We measured relative rates of passage of radioactive markers, mode of calcium (Ca) uptake, paracellular movement and the opening of voltage‐sensitive Ca channels (VSCCs) along the GIT with and without oral vitamin D3 supplementation. The ratio of relative absorption of labelled 45Ca to [14C]polyethylene glycol ([14C]PEG) indicated that within 24 h more than 88% of the Ca in the diet had been absorbed. Most absorption occurred in the duodenum within 12 h. The contribution of the hindgut (caecum and proximal and distal colon) to total Ca absorption was small (approximately 11%). Only passive uptake occurred in the duodenum (serosal (S): mucosal (M) ratios approximately 1). Active uptake occurred in the hindgut (S:M > 2), although hindgut absorption appears to play a secondary role to passive uptake in the duodenum. Vitamin D3 supplementation had no effect on the mode of Ca uptake in either the small intestine or the hindgut. Although we found VSCCs in mole‐rat intestinal epithelial cells, they occurred in very low concentrations. Calcium influx through VSCCs did not change following vitamin D stimulation. Furthermore, mole‐rats pretreated with intraperitoneal (I.P.) 1,25(OH)2D3 showed no enhancement of VSCC Ca uptake, indicating that active uptake plays a minor role, if any, in GIT mineral absorption. Our data support the hypothesis that intestinal Ca transport in mole‐rats is independent of both genomic and non‐genomic vitamin D mediation.
Primary neural involvement in renal haemodynamic and functional responses to prolonged stimulation of atrial receptors in anaesthetized dogs
Authors: Majid DS , Karim F
Published: December 2014

To determine the precise contributory role of neural and humoral factors in the efferent mechanism of the atrial receptor‐renal reflex, we have examined the effects of prolonged (45 min) stimulation of left atrial receptors on renal haemodynamics and function simultaneously in both kidneys (right kidney intact and left kidney denervated) of anaesthetized dogs. Aortic pressure in these dogs was held constant by means of an arterial reservoir connected to the aorta; heart rate changes were prevented by blocking beta 1‐adrenoceptor activity with atenolol (2 mg kg‐1 i.v.). Localized stimulation of atrial receptors in six dogs increased renal blood flow (6 +/− 2%), creatinine clearance (11 +/− 4%), urine flow (9 +/− 3%), sodium excretion (14 +/− 7%) and osmolal excretion (10 +/− 4%), and decreased free water clearance (14 +/− 7%) in intact kidneys, but led to no changes in denervated kidneys. In an additional four dogs, cooling the vagus nerves to 6–7 degrees C or cutting them in the neck abolished the renal responses to stimulation of atrial receptors in these stabilized preparations. These data clearly demonstrate that the renal responses to prolonged stimulation of atrial receptors are primarily mediated via myelinated vagal afferents and renal sympathetic efferents.
Changes in tension of slow motor units in rat medial gastrocnemius during constant‐rate stimulation at different frequencies
Authors: Celichowski J , Grottel K
Published: December 2014

Changes in tension of slow motor units in the medial gastrocnemius muscle of the rat were measured and compared in three fatigue tests, each of 4 min duration. In one of these tests motor unit tetani were evoked by repeated trains of stimuli of the standard frequency, 40 Hz, while in other tests frequencies of 20 and 60 Hz were used. Tetanic tension initially decreased in the majority of units during these three tests, then potentiated and, in the last part of the fatigue test, the tension was normally stable. Initial changes in tension were greatest in the fatigue tests with the lowest stimulation frequency (20 Hz) and smallest or even absent during tests with the stimulation frequency of 60 Hz. Moreover, initial changes in tension occurred for the longest period of time when the lowest frequency of stimulation (20 Hz) was used. Some of the motor units showed a slow decrease in tension in the last part of tests, especially when frequencies of 60 and 40 Hz were used. These results show that the tension of repeated unfused tetani of a slow motor unit is not constant, even during constant frequency stimulation, and changes in tension are greater in less fused tetani.
Phosphate transport via Na+ ‐Pi cotransport and anion exchange in lactating rat mammary tissue
Authors: Shillingford JM , Calvert DT , Beechey RB , Shennan DB
Published: December 2014

Inorganic orthophosphate (Pi) transport, using 32P‐labelled orthophosphate as tracer, by lactating rat mammary tissue has been examined using both tissue explants and the intact perfused gland. Pi uptake was predominantly via a Na+ ‐dependent pathway. Li+, however, unlike choline, was able to partially substitute for Na+. In addition, Pi release from tissue explants preloaded with 32Pi was stimulated by reversing the Na+ gradient. Thus transferring mammary explants from a buffer containing Na+ to one which was Na+ free (choline replacement) doubled the Pi efflux rate constant. The uptake of Pi by tissue explants was saturable with respect to external Pi, having apparent K(m) and V(max) values of 1.13 mM and 3.36 mmol (kg cell water)‐1 (15 min)‐1, respectively. The stimulation of Pi uptake by tissue explants by external Na+ was also saturable; the K(m) for Na+ was 9.7 mM. These results, taken together, suggest that the Na+ ‐dependent pathway is a Na+ ‐Pi cotransport mechanism. The transport of Pi by the perfused lactating rat mammary gland was examined using a rapid, paired‐tracer dilution technique. Pi uptake by the perfused gland was found to be Na+ dependent and displayed saturable kinetics. The results suggest that the Na+ ‐Pi cotransporter is situated at the basolateral aspect of the secretory cells. The release of Pi from preloaded tissue explants was trans‐accelerated by external Pi but not by Cl‐ or SO4(2‐). However, external Pi stimulated Pi efflux with low affinity.
Peroxidase and kallikrein in atropine‐resistant secretion of submandibular saliva on parasympathetic nerve stimulation in anaesthetized rats
Authors: Garrett  , Anderson LC , Zhang XS , Proctor GB
Published: December 2014

Flow of submandibular saliva and the constituents secreted during chorda‐lingual nerve stimulation at 40 Hz (3 x 10 min) were studied after alpha‐ and beta‐adrenergic blockade, and in the absence (control) or presence of cholinergic blockade in anaesthetized rats. Peroxidase and true tissue kallikrein (rK1) were assessed to gain insight into the effects of the non‐adrenergic, non‐cholinergic (NANC) transmitters on protein secretion by acini and granular tubules, respectively. From control glands there was an overall mean flow of 181 +/− 15 microliters g‐1 min‐1, with no significant differences between the three periods. Secretion from atropinized glands was approximately 20% of that from control glands in the first 10 min, decreasing progressively to approximately 6% in the final period. Protein outputs from control glands showed no significant differences for the three periods (0.23 +/− 0.05 mg g‐1 min‐1). Protein outputs from atropinized glands were similar to controls in the first 10 min and then decreased significantly. Peroxidase output from control glands increased progressively (from 31 +/− 7 to 243 +/− 68 pmol dichlorofluorescein (DCF) g‐1 min‐1) but in saliva from atropinized glands the overall mean output was only 4.5 +/− 0.8 pmol DCF min‐1 ml‐1, with a progressive decrease between samples. Outputs of rK1 from control glands were similar for all samples (20.6 +/− 4.0 nmol AFC g‐1 min‐1), but there was a significantly smaller and decreasing output of rK1 from atropinized glands. In conclusion, NANC transmitters released from parasympathetic nerves during stimulation at high frequency appear to have little influence on the secretion of protein from rat submandibular acini and granular tubule cells when acting in isolation. This contrasts with their effects on amylase secretion from rat parotid glands under similar circumstances.
Effects of moderate hypothermia on baroreflex and pulmonary chemoreflex heart rate response in decerebrate ferrets
Authors: Zheng F , Kidd C , Bowser-Riley F
Published: December 2014

The effects on the baroreceptor reflexes and pulmonary reflexes of moderate immersion hypothermia (core temperature, 30.2 +/− 0.07 degrees C) have been investigated in the decerebrate ferret. Baroreflex sensitivity was estimated from the relationship between change in cardiac interval and change in systolic blood pressure following i.v. bolus injection of phenylephrine. The responses to phenylephrine in ferrets were best fitted by two linear slopes with an initial shallow slope, a, followed by a steeper slope, b. The slope or sensitivity of b was increased significantly by moderate cooling (n = 6 animals, 36 responses, P < 0.05). Pulmonary J‐receptor reflex sensitivity was assessed by i.v. injection of phenylbiguanide (PBG), which evokes a dose‐dependent bradycardia. The bradycardic response was unaltered by the hypothermia (n = 6 animals, 88 responses). Electrical stimulation of the right peripheral vagal nerve was employed to assess effects on the efferent components of the reflexes. The bradycardia, in response to stimulation, was significantly increased by moderate cooling at all stimulation frequencies (n = 8 animals, 88 responses, P < 0.001). Thus the results suggested that baroreceptor heart rate reflex sensitivity was enhanced by the moderate hypothermia. At least one component of the enhanced baroreflex response may be the result of changes in the efferent pathway of the reflex response. However, the absence of effect of PBG may indicate a differential afferent and efferent organization of pulmonary J‐receptors compared with baroreceptors.
Cutaneous vascular control in the arms of women with postmastectomy oedema
Authors: Stanton AW , Levick  , Mortimer PS
Published: December 2014

The control of forearm skin blood flow was examined in the swollen arms of twelve women with oedema caused by breast cancer treatment. The swollen arm was compared with the opposite unaffected (control) arm. Using laser Doppler flux (LDF) and continuous finger blood pressure (BP) measurements, vascular control was tested by applying a range of provocations previously shown to alter cutaneous vascular resistance (CVR) in healthy subjects. The tests and the accepted mechanism were: post‐ischaemic hyperaemia (locally mediated vasodilatation), inspiratory gasp and cool reflex (both sympathetically mediated vasoconstriction), arm dependency (locally mediated vasoconstriction), and core heat load (sympathetically mediated vasodilatation). CVR was calculated as BP/(LDF‐biological zero). Three differences between the control and swollen arms were identified. (i) The laser Doppler biological zero signal was significantly higher on the swollen side (P = 0.005, Student's paired t test). (ii) Baseline LDF was significantly lower on the swollen side (P = 0.002), and apparent CVR correspondingly higher. (iii) Cumulative reactive hyperaemia (area under the LDF curve above baseline) was significantly less on the swollen side (P = 0.03), although peak flux was not significantly different. Inspiratory gasp, cool reflex, arm dependency and core heat load produced changes of similar magnitude in both arms. It appears that sympathetic neural control and local vasoconstrictor control in arm dependency are normal in arm lymphoedema but that locally mediated vasodilator control is impaired. In addition, baseline skin blood flow may be reduced in this condition. The results provide no support for impairment of vascular tone as a contributory factor to the oedematous state.
Accumulation of the endogenous L‐arginine analogue NG‐monomethyl‐L‐arginine in human end‐stage renal failure patients on regular haemodialysis
Authors: Mendes Ribeiro AC , Roberts NB , Lane C , Yaqoob M , Ellory JC
Published: December 2014

We measured plasma levels of L‐arginine, its analogue NG‐monomethyl‐L‐arginine (L‐NMMA), and related amino acids in normal subjects and uraemic patients (n = 31), before and after haemodialysis. Plasma levels of L‐arginine were reduced to less than half of normal values in uraemic subjects compared with controls, and were not affected by haemodialysis. L‐NMMA was not detectable in non‐uraemic subjects, but markedly elevated in uraemic patients. In parallel, we used human red blood cells as a model to study the effect of L‐NMMA upon the transport of L‐arginine. L‐NMMA trans‐stimulated L‐arginine transport significantly, confirming that L‐arginine and L‐NMMA share common transport pathways. Our results suggest altered L‐arginine metabolism and the presence of an increased concentration of a NO synthase inhibitor in uraemia. We propose that alterations in plasma L‐arginine levels and increased production of L‐arginine analogues will alter NO synthesis and may help to explain some pathological changes seen in uraemia.
G protein regulation of alveolar ion channels: implications for lung fluid transport
Authors: Kemp PJ , Olver RE
Published: December 2014

Vectorial ion flow across the alveolar epithelium provides the driving force for lung fluid secretion in the prenatal lung and for fluid reabsorption at birth and thereafter into adult life. Fluid secretion is dependent upon ‘active’ accumulation of Cl‐ into the lumen of the developing lung and any factor which interupts the production of this liquid template results in life‐threatening abnormalities in lung growth. The direction of fluid flow is reversed at birth to bring about the reabsorption of the lung fluid so that gaseous exchange can be initated successfully in the neonate. This functional switch at birth involves active Na+ reabsorption; failure of this mechanism to activate adequately contributes to respiratory distress in the newborn. Although beta 2‐adrenoceptor‐cAMP‐protein kinase activation provides a basic model for the switch, it is clear that local regulation of many of the components in the switching cascade are important to the overall efficiency with which it is achieved. Co‐localized with apical Cl‐ and Na+ channels are pertussis toxin‐sensitive G proteins, which exert their regulatory effects principally by direct protein‐channel interactions. The modulation of channels by local G proteins is finely tuned by negative feedback mechanisms, which may include a novel double‐bond specific fatty acid regulation of G protein turnover and the paracrine effects of locally produced eicosanoids. An understanding of how these overlapping pathways integrate to produce the smooth and ordered transition from Cl‐ secretion to Na+ absorption will allow the design of rational treatments for conditions that are characterized by disfunctional lung fluid homeostasis.
Evidence for independent Cl‐ and HCO3‐ secretion and involvement of an apical Na(+)‐HCO3‐ cotransporter in cultured rat epididymal epithelia
Authors: Chan HC , Ko WH , Zhao W , Fu WO , Wong PY
Published: December 2014

Electrogenic chloride and bicarbonate secretion by cultured rat epididymal epithelia was studied using the short‐circuit current (ISC) technique. When incubated in normal solution, 8‐(4‐chlorophenylthio)‐adenosine 3',5'‐cyclic monophosphate (cpt‐cAMP) caused a rise in the ISC, which was attributable to Cl‐ and HCO3‐ secretion. Cl‐ secretion was found to contribute to the initial transient phase, whereas HCO3‐ secretion contributed to the sustained phase of the response. HCO3‐ secretion involves a basolaterally placed Na(+)‐H+ exchanger and apical anion channel, most probably the cystic fibrosis transmembrane conductance regulator (CFTR). There is also evidence that an apical electrogenic Na(+)‐HCO3‐ cotransporter is involved in HCO3‐ exit. CFTR accounted for 70% of HCO3‐ secretion, while the Na(+)‐HCO3‐ cotransporter accounted for 30%. The possibility that the cotransporter may serve as an alternative pathway for HCO3‐ secretion in cystic fibrosis is discussed.
Orthophosphate salts induce calcium current recovery from blockade by gadolinium in isolated guinea‐pig ventricular myocytes
Authors: Le Guennec JY , Lacampagne A , Garnier D
Published: December 2014

Using the whole‐cell configuration of the patch‐clamp technique, we studied the incomplete recovery of the high voltage‐activated calcium current (ICa,L) from a complete blockade by 10 microM gadolinium. The study was performed on isolated guinea‐pig ventricular myocytes. ICa,L recovery depended on the duration of application of Gd3+: for a mean application time of 1.63 +/− 0.45 min, a recovery to 67 +/− 22% of the initial current amplitude (n = 12 cells) was observed; when the application lasted 5.1 +/− 1.2 min ICa,L recovered to 27 +/− 13% (n = 14 cells). The partial recovery of ICa,L was accompanied by a slowing of the inactivation phase of the current. IF, during the incomplete recovery, cells were exposed to a solution containing 330 microM of an orthophosphate salt, such as NaH2PO4 or KH2PO4, the current amplitude increased to 80 +/− 13% of the initial current (n = 10 cells) in a reversible manner. However, the slowing of the inactivation phase was maintained. Our results show that the partial recovery of ICa,L from blockade by gadolinium is due to an interaction of the blocker with an extracellular part of the channel, possibly one involved in voltage‐dependent inactivation.
Separation of the components of the delayed rectifier potassium current using selective blockers of IKr and IKs in guinea‐pig isolated ventricular myocytes
Authors: Heath BM , Terrar DA
Published: December 2014

Delayed rectifier potassium current (IK) was investigated in guinea‐pig isolated ventricular myocytes under voltage‐clamp conditions (‘switched’ single electrode clamp), using selective blockers and/or different activation protocols to separate its rapid (IKr) and slow (IKs) components. The class III antiarrhythmic compound E4031 (5 microM) was used to block IKr and the anaesthetic drugs propofol (100 microM) or thiopentone (100 microM) to block IKs. In all experiments L‐type calcium currents were blocked with nifedipine (2 microM). Complementary effects of E4031 and the anaesthetic drugs on the components of IK were observed. The E4031‐sensitive current (IKr) resembled the current remaining in the presence of the anaesthetics and, likewise, the anaesthetic‐sensitive current (IKs) resembled the current remaining in the presence of E4031. Under the conditions of these experiments, the relative contribution of the two components to total IK tail current was found to be approximately equal after a 400 ms depolarization to +40 mV. For example, IKr was 58 +/− 10% of total IK tail current when measured as the E4031‐sensitive current, 41 +/− 6% as the propofol‐insensitive current and 43 +/− 7% as the thiopentone‐insensitive current. In the presence of both E4031 and propofol or thiopentone the IK tail current deactivating at ‐40 mV was completely eliminated, leaving a residual current during the pulse which reversed at ‐46 +/− 1 mV. To avoid complication of the ‘envelope of tails’ test with this residual current, the tail:pulse ratio was calculated for the anaesthetic‐sensitive component and this was constant, consistent with block of a single component of IK. Forskolin (1 microM) enhanced the current most consistent with IKs. Propofol (300 microM) caused a 64 +/− 3% increase in action potential duration in the presence of both E4031 (5 microM) and nifedipine (2 microM), consistent with an important role for IKs in the repolarization of the action potential in the guinea‐pig heart. The observations therefore provide further support for separate components of IK with different characteristics in the guinea‐pig heart; it appears that E4031 and propofol or thiopentone are useful complementary tools for their separation.
The effect of bile acid on the activation of amiloride‐sensitive sodium channels in frog skin
Authors: Lima MS , Ferreira HG , Ferreira KT
Published: December 2014

The effect of the bile acid, deoxycholic acid (DOC), on the transport properties of isolated frog skin was studied under short‐circuit conditions. The addition of DOC (1 mM) to the apical side of the frog skin induced a threefold increase in the short‐circuit current (Iac). This effect was inhibited by amiloride. DOC also increased the conductance of the preparation by two different mechanisms. At low concentrations (< 2.5 mM) it activated amiloride‐sensitive sodium channels. At higher concentrations of DOC, basolateral‐apical unindirectional fluxes, measured with 22Na+, 36Cl‐. [14C]mannitol and [14C]inulin, showed a selective increase in the permeability to Na+, Cl‐ and mannitol in relation to [14C]inulin. These data suggest that sodium and chloride ions use the same diffusional pathway across the preparation. This pathway discriminates between NaCl and mannitol, and discriminates even more in relation to inulin. The effects of DOC are additive to those of cAMP (1 mM). ADH (20 mU ml‐1), prostaglandin E2 (0.1 microM) or forskolin (10 microM). It is concluded from our study that the final effect of DOC in stimulating the Isc in frog skin is through the activation of amiloride‐sensitive sodium channels. However, since DOC is liposoluble, a direct activation of an adenylate cyclase or of phosphokinase A cannot be excluded.
Effects of ingested fluids on exercise capacity and on cardiovascular and metabolic responses to prolonged exercise in man
Authors: Maughan RJ , Bethell LR , Leiper JB
Published: December 2014

It is well established that the ingestion of carbohydrate‐containing drinks can improve the performance of prolonged exercise. The present study examined the effects of ingestion of water and two dilute glucose‐electrolyte drinks on exercise performance and on cardiovascular and metabolic responses to exercise. Twelve subjects exercised to exhaustion on a cycle ergometer at a workload corresponding to 70% of maximum oxygen uptake (VO2,max) on five occasions each separated by 1 week. The first trial served to accustom subjects to experimental conditions. On one trial, no drinks were given and on the others subjects drank 100 ml every 10 min. Drinks consisted of water, an isotonic glucose‐electrolyte solution (I: 200 mmol/l glucose; 35 mmol/l NA2; 310 mosmol/kg) and a hypotonic glucose‐electrolyte solution (H: 90 mmol/l glucose; 60 mmol/l Na+; 240 mosmol/kg). Treatment order was randomized. Blood and expired air samples were taken and heart rate and rectal temperature measured at intervals during exercise. Median exercise time was greatest for treatment H (110.3 min) followed by treatment I (107.3 min), water (93.1) and no drink (80.7). Endurance times differed significantly overall, and for pairwise comparisons (P < 0.01) between the no‐drink trial and both treatments H and I: a difference between water and no drink was seen at the 5% level. At exhaustion, a significant treatment difference was found for the change in plasma volume, with the greatest decrease (6.7%) on the no‐drink trial and the smallest decrease (0.5%) on treatment H. Significant treatment effects were also observed for heart rate, rectal temperature and serum osmolality. The results suggest that the ingestion of glucose‐electrolyte drinks can improve exercise performance even when the amount of added glucose is small, and that performance may also be enhanced, albeit to a lesser degree, by ingestion of water.
Regulation of the adrenocorticotrophin response to stress by the central nucleus of the amygdala in rats depends upon the nature of the stressor
Authors: Marcilhac A , Siaud P
Published: December 2014

The regulatory role of the medial (CeM) or the lateral (CeL) part of the central nucleus of the amygdala on the hypothalamo‐pituitary‐adrenal axis response to stress was investigated in male rats. Basal and restraint‐ or lipopolysacharride (LPS)‐induced plasma adrenocorticotrophic hormone (ACTH) levels were measured 7 days after sham operation or lesion of the CeM or CeL. CeM or CeL lesion did not change basal ACTH concentrations. In control rats, restraint or LPS injection induced a robust increase in ACTH secretion. CeL lesion did not modify the stress‐induced increment in ACTH release. CeM lesion significantly decreased the ACTH response to restraint and potentiated the ACTH response to LPS injection. Our findings demonstrate that the CeM exerts complex influences on the corticotrophic response to stress, being either stimulatory or inhibitory, depending on the nature of the stressor.
Length‐dependent mechanisms in single cardiac cells
Authors: White E
Published: December 2014

This brief review looks at recent work investigating length‐dependent mechanisms in single cardiac cells. Studies using the mechanically simple single cardiac cell have confirmed much of the data previously reported in multicellular preparations, although some differences between single cell and multicellular studies have been found. Electrical studies have been able to investigate the effects of stretch on ion channels and have concentrated upon the exciting discovery of many types of stretch‐activated channels in the heart. These channels may explain the occurrence of length‐dependent changes in pacemaker activity and stretch‐activated arrhythmias in the whole heart. Prolonged stretch can lead to hypertrophy, and single cell studies have been able to characterize the sequence of events leading from membrane stretch to altered protein expression. It appears from these studies that the role of angiotensin II is important.
Acetylcholine‐evoked potassium transport in the isolated guinea‐pig pancreas
Authors: Rosado JA , Singh J , Salido GM , Garcia LJ
Published: December 2014

In this study, K+ concentration was measured in effluent samples from superfused guinea‐pig pancreatic pieces in control conditions and during stimulation with ACh, employing the technique of flame photometry. ACh (10(‐7)‐10(‐5) M) evoked a dose‐dependent and sustained increase in K+ concentration in the effluent (K+ release). The removal of Ca2+ from the superfusing medium and the addition of 10(‐4) M EGTA caused a significant (P < 0.05) reduction in the ACh‐evoked K+ efflux. Replacement of extracellular Cl‐ in the superfusing physiological salt solution with NO3‐ abolished the ACh‐induced K+ efflux. In contrast, when Cl‐ was replaced with Br‐, ACh still evoked marked K+ release. Pretreatment of pancreatic segments with the loop diuretic furosemide (10(‐4) M) resulted in an inhibition of K+ efflux elicited by ACh. Stimulation of pancreatic segments with the Na(+)‐K(+)‐ATPase inhibitor ouabain (10(‐3) M) caused a large efflux of K+. In the continuous presence of ouabain, ACh application elicited no further change in the K+ release. The results indicate that ACh‐evoked K+ release from guinea‐pig pancreatic segments is sensitive to ouabain, Cl‐, furosemide and extracellular Ca2+ and that only the basal efflux is augmented by ouabain. The findings provide further evidence that a diuretic‐sensitive coupled Na(+)‐K(+)‐Cl‐ cotransport system operates in the guinea‐pig pancreas, as it does in other similar transporting epithelia, to bring about K+ mobilization.
An early transient current is associated with hyposmotic swelling and volume regulation in embryonic chick cardiac myocytes
Authors: Hall SK , Zhang J , Lieberman M
Published: December 2014

Hyposmotically induced changes in membrane conductance were measured in embryonic chick cardiac myocytes using conventional and perforated patch‐clamp recording techniques; simultaneous measurements of cell volume were made from the video image of the voltage‐clamped cell. Hyposmotic challenge was associated with a rapid, transient current coincident with the onset of cell swelling; cell volume subsequently recovered towards control values (regulatory volume decrease; RVD). The transient swelling‐induced current (I(swell)) reversed at +15 mV, and was not found to be carried exclusively by any single ion in the physiological solutions. I(swell) was abolished by gadolinium (Gd3+), a blocker of stretch‐activated ion channels, and was absent when the cytoskeleton was disrupted by treatment with cytochalasin B. I(swell) was also prevented when intracellular [Ca2+] was buffered with BAPTA AM. Under those experimental conditions which prevented the generation of I(swell), cell volume regulation failed so that the cells remained swollen in hyposmotic solution. Our data reveal a functional relationship between I(swell) and RVD, whereby I(swell) is a necessary prerequisite, although not exclusively sufficient, for volume recovery following cell swelling. We propose that I(swell) is an important early signalling event which activates subsequent mechanisms to regulate cell volume.
Osmotic flow transients during acetylcholine stimulation in the perfused rat submandibular gland
Authors: Nakahari T , Steward MC , Yoshida H , Imai Y
Published: December 2014

Osmotic stress was applied to the perfused rat submandibular gland during steady‐state fluid secretion. Alterations of perfusate osmolarity, by addition or withdrawal of sucrose or NaCl, caused transient changes in secretory rate during continuous stimulation with 1 microM acetylcholine (ACh). Hyposmotic perfusates transiently increased, and hyperosmotic perfusates transiently reduced, the secretory rate. The transients were attributed to changes in osmotic flow resulting from changes in the instantaneous transepithelial osmotic gradient. The time course of the change in interstitial osmolarity was determined by using a Cl‐ electrode to record the changes in interstitial Cl‐ concentration following a step change in perfusate Cl‐ concentration. From the calculated changes in interstitial osmolarity and the resulting changes in secretory rate, the osmotic water permeability of the secretory pathway was estimated to be greater than 15.0 +/− 1.2 microliter (mosmol 1‐1)‐1 min‐1 (g wet weight)‐1 (9.8 x 10(‐6) +/− 0.8 x 10(‐6) l atm‐1s‐1g‐1). The transepithelial gradient required to sustain steady state, ACh‐evoked secretion would therefore be less than 16 mosmol l‐1 NaCl, which is consistent with previous micropuncture data indicating that the luminal fluid is approximately isosmotic.
Effects of nitric oxide on diaphragmatic muscle endurance and strength in pigs
Authors: Albertini M , Lafortuna C , Aguggini G
Published: December 2014

The aim of the study was to evaluate the effects of nitric oxide (NO) on diaphragmatic fatigue in fifteen anaesthetized, mechanically ventilated pigs, divided into three groups. The animals were pre‐treated with indomethacin (3 mg kg‐1, i.v.) to block the cyclo‐oxygenase pathway. To group 1 pigs (n = 6) NG‐nitro‐L‐arginine methyl ester (L‐NAME, 5 mg kg‐1 i.v.) was administered as a bolus to block endogenous NO production, while group 2 pigs (n = 6) were infused with sodium nitroprusside (SNP, 0.023 mg kg‐1, i.v.), a donor of NO. Group 3 pigs (n = 3) were used as the controls. We evaluated diaphragmatic strength by measuring the transdiaphragmatic pressure (P di) generated during bilateral phrenic nerve stimulation at 10, 20, 30 and 50 Hz, 15 V, while the diaphragmatic endurance was assessed by a 30s stimulation at 10 Hz, 15 V. Diaphragmatic index was assessed as the ratio of peak force between single twitches performed before and after the 30 s stimulation west. We also evaluated mean systemic (MAP) and pulmonary (MPAP) arterial pressures, pulmonary wedge pressure (PW), systemic (SVR) and pulmonary vascular resistance (PVR) and cardiac output (CO). L‐NAME increased MAP, MPAP, PW, SVR and PVR, but decreased CO. SNP caused a decrease in MAP, MPAP, PW and SVR, while PVR and CO did not change. The main finding of this study was that diaphragmatic strength was not significantly weakened after L‐NAME administration, except at 10 Hz, while it did not change after SNP infusion. However, both L‐NAME and SNP caused significant decreases in diaphragmatic endurance capacity. The fatigue appearing after L‐NAME is probably correlated with a decline in diaphragmatic blood flow, as evidenced by the increase in SVR and the decrease in CO, and consequently in oxygen supply. In contrast, the decrease in endurance capacity after SNP infusion can be attributed to a direct action of NO on skeletal muscle.
The role of chloride in the lens of the eye
Authors: Zhang JJ , Jacob TJ
Published: December 2014

Until recently, the investigation of membrane ion transport mechanisms and their relationship with cataract formation has mainly focused on sodium, potassium and calcium. The specific role of chloride in solute transport within the lens has been given little attention. Rather, chloride was considered as simply the counterion to sodium. The purpose of this review is to emphasize the importance of chloride and its involvement in the membrane ion transport systems within the lens. We summarize the general physiological and chemical properties of the chloride ion in the lens, with reference to the regional ion fluxes generated by its special anatomical and electrical structure. We also present our current knowledge of the principal ion transport mechanisms associated with chloride, with particular emphasis on Cl‐ channels, and discuss their possible physiological significance. Maintenance of a constant cell volume is an evolutionarily ancient homeostatic process and we present some important findings associated with volume regulatory mechanisms in the whole lens and in single lens cells. Finally, we review and discuss the link between cataract formation and chloride channel dysfunction.
The mode of action of several opioids on cardiac muscle
Authors: Wu C , Fry CH , Henry J
Published: December 2014

The objective of the experiments was to investigate the cellular basis of the inotropic effect on myocardium of several opioids which have been implicated in producing cardiotoxic effects in human poisoning. Opioids exerted negative inotropic effects, with half‐maximal concentrations between 10 microM (dextropropoxyphene) and 118 microM (pethidine); all agents reduced the magnitude of the intracellular Ca2+ transient and the L‐type Ca2+ current, ICa, over a similar concentration range to that which reduced twitch tension. The depression of ICa correlated positively with the value of the opioid oil‐water partition coefficient. Effects were not antagonized by the opioid receptor antagonist naloxone. Action potential upstroke rate was also reduced but at significantly higher concentrations. Resting potential and action potential duration were not consistently affected; none of the opioids tested altered intracellular pH. These data suggest that opioids exert a negative inotropic effect by their action on ICa; blockade of the Na+ current is not great enough to exert a significant action. The lack of effect of naloxone implies the actions are independent of the opioid receptor. The correlation of effects with the oil water partition coefficient implies a non‐specific effect dependent on the hydrophobicity of the agent.
Identification of projections from the central nucleus of the amygdala to the paraventricular nucleus of the hypothalamus which are immunoreactive for corticotrophin‐releasing hormone in the rat
Authors: Marcilhac A , Siaud P
Published: December 2014

Corticotrophin‐releasing hormone (CRH) immunoreactivity was detected in neurons of the central nucleus of the amygdala that were retrogradely labelled by injection of a fluorescent tracer (True Blue) into the paraventricular nucleus of the hypothalamus (PVN). The double‐labelled neurons were located mainly in the medial subdivision of the central nucleus and appeared to comprise less than one‐fifth of the descending pathway. These results suggest that CRH may act as a neurotransmitter in the amygdalo‐hypothalamic pathway.
Responses of neurones in the medullary raphe nuclei to inputs from visceral nociceptors and the ventrolateral periaqueductal grey in the rat
Authors: Snowball RK , Dampney RA , Lumb BM
Published: December 2014

The ventrolateral periaqueductal grey matter (PAG) is believed to have a role in mediating cardiovascular responses to noxious visceral stimuli. The present study was carried out as a first stage in establishing whether the ventrolateral PAG may exert these influences after a relay in the caudal medullary raphe nuclei (nucleus raphe obscurus and nucleus raphe pallidus). Single unit extracellular recordings were made from neurones in the caudal raphe nuclei and, for comparison, in the more rostral nucleus raphe magnus in Saffan‐anaesthetized and paralysed rats. Neurones in the mid‐line medulla were tested for their responses to electrical stimulation at chemically identified depressor sites in the ventrolateral PAG and to noxious visceral stimuli (distensions of the urinary bladder and electrical stimulation of the greater splanchnic nerve). Fifty‐two per cent of caudal and 74% of rostral mid‐line neurones gave short latency excitatory responses to stimulation of depressor sites in the ventrolateral PAG. Of the neurones that were also tested with noxious visceral stimuli, 5% of the caudal and 47% of the rostral neurones responded to bladder distension, while 33 and 35%, respectively, of caudal and rostral neurones responded to splanchnic nerve stimulation. These results indicate that many mid‐line medullary neurones receive inputs from both the ventrolateral PAG and visceral nociceptors and may, therefore, be part of the output pathway by which the ventrolateral PAG produces integrated physiological responses to noxious visceral stimuli.
Direct vascular effects of plantain extract in rats
Authors: Orie NN
Published: December 2014

Responses of the aorta and portal veins isolated from rats to aqueous extract of plantain (Musa paradisiaca) were studied. The extract produced concentration‐dependent relaxation in both noradrenaline‐ and KCl‐contracted aortic rings. The maximum relaxation in noradrenaline‐contracted rings was 52.49 +/ࢤ 6.63% and in KCl‐contracted rings was 77.51 +/ࢤ 2.52% of the initial tensions developed in response to the contractile agents. The extract also produced significant (P < 0.01) inhibition of the maximum aortic contractile response to noradrenaline and completely abolished the spontaneous contractions of the portal veins. Serotonin (5‐hydroxytryptamine), unlike the extract, produced contraction rather than relaxation of the aortic rings. The results show a non‐specific relaxing and inhibiting effect of plantain extract on aortic and portal smooth muscles, an effect that is not attributable to its abundant serotonin content.
The effect of passive stretch on the response of the fetal rabbit ductus arteriosus to indomethacin, noradrenaline and prostaglandin E2
Authors: Smith GC
Published: December 2014

The aim of this study was to determine the effect of varying stretch of the ductus arteriosus on its contractile response to indomethacin and noradrenaline, and its relaxant response to prostaglandin (PG) E2. Isolated rings of ductus arteriosus obtained from fetal New Zealand White rabbits at 28 days gestation were mounted in vitro for measurement of isometric tension by a transducer connected to a vernier control. The responses of the ductus to drugs at varying degrees of passive stretch were corrected to a standard contraction in response to 65 mM potassium at a standard level of stretch. Increasing stretch across the range 1.0‐5.9 mN increased the contractile response to indomethacin and noradrenaline (the latter in the presence of 1 microM indomethacin and 1 or 10 nM PGE2) in a virtually identical manner. The sensitivity of the vessel to noradrenaline in the presence and absence of indomethacin and its sensitivity to the relaxant effect of PGE2 in the presence of indomethacin were unaffected by increasing stretch. The extent of contractile tone present which was not inhibited by endogenous PGE2 increased with increasing stretch. It was concluded that: (1) the contractile response to indomethacin can be profoundly altered by the degree of spontaneous tone in the vessel; (2) the magnitude of the contraction induced by indomethacin is not a good index of the degree of inhibition exerted by locally produced PGs in the vessel; and (3) locally produced PGs are likely to have a physiological role in maintaining patency of the ductus arteriosus in utero.
Integrative role of medullary neurons of the cat during exercise
Authors: Nolan PC , Waldrop TG
Published: December 2014

The co‐ordinated cardiovascular and respiratory responses observed during exercise are mediated by both afferent activation arising in contracting skeletal muscles and descending central drive originating in brain regions rostral to the medulla. Even though integration of these two mechanisms must occur in order to produce alterations in cardiorespiratory activity proportional to the intensity of the exercise, little is known about how this integration occurs. The purpose of the present study was to examine the role of medullary sites in the integration of exercise drives to the cardiovascular and respiratory systems. The responses of neurons in the ventrolateral medulla and the lateral tegmental fields to contraction of hindlimb muscles (elicited by stimulation of the L7 S1 ventral roots) and to activation of simulated central command (caudal hypothalamic stimulation) were examined in anaesthetized cats. Muscular contraction evoked an increase in discharge frequency in 59% (24/41) of the medullary neurons; 58% (14/24) of these neurons excited by muscular contraction displayed an immediate increase and 42% (10/24) had a more delayed increase in discharge frequency. Eighty‐three per cent (10/12) of neurons rapidly excited by hindlimb muscle contraction were inhibited by hypothalamic stimulation. In contrast, most neurons which showed a delayed increase in discharge frequency during muscle contraction were either excited by hypothalamic stimulation (5/10) or unaffected (4/10). The majority of medullary neurons studied possessed a basal discharge related to the cardiovascular, respiratory and/or sympathetic cycles. These findings demonstrate that both feedback from contracting muscles and descending central command impinge upon individual medullary neurons. This is consistent with the idea that medullary neurons are important in integrating both the central drive and peripheral reflexes controlling the cardiorespiratory responses to exercise.
Glycosaminoglycan depletion greatly raises the hydraulic permeability of rabbit joint synovial lining
Authors: Scott D , Coleman PJ , Mason RM , Levick
Published: December 2014

The hydraulic resistance of the synovial lining of a joint is important for retention of intraarticular lubricant. The resistance has been attributed to synovial interstitial glycosaminoglycans. This was tested by depletion of hyaluronan and chondroitin sulphates from synovium in five rabbit knees in vivo under anaesthesia, using testicular hyaluronidase. The enzyme raised synovial permeability to fluid 5‐ to 7‐fold‐substantially more, in fact, than predicted by a recent model. The results prove that hyaluronan and/or chondroitin sulphate are important sources of hydraulic resistance in synovium.
Relationship between membrane potential, delayed rectifier K+ currents and hypoxia in rat pulmonary arterial myocytes
Authors: Turner JL , Kozlowski RZ
Published: December 2014

Pulmonary arteries constrict in response to hypoxia, a process thought to involve oxygen sensing by K+ channels. We therefore investigated the effects of hypoxia on voltage‐activated K+ currents in myocytes isolated from rat small pulmonary arteries using the patch‐clamp recording technique. Experiments with iberiotoxin and intracellularly applied Ca2+ chelating agents revealed that hypoxia (PO2, 20–30 mmHg; throughout) inhibited the Ca(2+)‐insensitive component of the delayed voltage‐activated outward K+ current. Hypoxia did not affect the membrane potential of these cells until they were depolarized by extracellular application of 20 mM K+, current injection or endothelin‐1. Hypoxia caused little depolarization in the presence of prostaglandin F2 alpha, an agonist which was ineffective at inducing depolarization. These results suggest that an initial ‘priming’ depolarization may confer a sensitivity to hypoxia by activating delayed rectifier (Kv) channels. Once active, these channels can then be closed by hypoxia, leading to further depolarization. It is unlikely, therefore, that Kv channels are involved in controlling the resting membrane potential of these cells.
Gadolinium blocks the delayed rectifier potassium current in isolated guinea‐pig ventricular myocytes
Authors: Hongo K , Pascarel C , Cazorla O , Gannier F , Le Guennec JY , White E
Published: December 2014

The effect of Gd3+ on the delayed rectifier potassium current (IK) in single guinea‐pig ventricular myocytes was tested using whole‐cell patch‐clamp techniques. It was found that Gd3+ blocked 70% of the IK tail current at a concentration of 100 microM. The EC50 was 24 microM. Action potential durations were, however, reduced, consistent with a predominant effect on depolarizing L‐type Ca2+ current (Ica.L). In the presence of 5 microM nifedipine Gd3+ prolonged the action potential. Using carbon fibres to stretch cells we observed that 10 microM Gd3+ was not effective in reducing a large stretch‐activated increase in resting calcium. Modelling studies using the OXSOFT HEART program suggest that this lack of response is influenced by blockade of repolarizing current but is best reproduced by additional blockade of Ca2+ extrusion via the Na(+)ࢤCa2+ exchanger. When Gd3+ is used as a blocker of stretch‐activated channels its actions upon both Ica.L and IK must therefore be accounted for.