The cellular basis of bladder instability.
Explore the source record for details and available documents.
Calcium↗
Biomedical subjects
C H Fry
Publications and source records attributed to C H Fry.
Conduction velocity and gap junction resistance in hypertrophied, hypoxic guinea-pig left ventricular myocardium.
The passive and active electrical properties of left ventricular myocardium were measured, using conducted action potentials and current clamp of isolated myocytes. The objective was to quantify changes of intracellular resistivity, Ri, during hypertrophic growth and the simultaneous imposition of cellular hypoxia. Ri was estimated from the time course of the rising phase of a conducted action potential using a solution of the two-dimensional cable equation. The thoracic aorta of guinea-pigs was constricted to induce left ventricular hypertrophy (LVH) and myocardium used 50 and 150 days post-operation. Conduction velocity increased in the earlier stage of LVH and declined in the later stage, compared with age-matched controls. Hypoxia reduced conduction velocity in all experimental groups. Ri increased only in the later stage of hypertrophy (253 +/- 39 Omega cm to 544 +/- 130 Omega cm) and was additionally increased by hypoxia in all groups (e.g. control myocardium 252 +/- 39 Omega cm to 506 +/- 170 Omega cm). The magnitude of the increase of Ri in hypertrophied, hypoxic myocardium can create conditions required to generate re-entrant arrhythmias.
Action Potentials↗
Membrane toxicity of opioids measured by protozoan motility.
The acute toxicity of some opioid drugs cannot solely be explained by a specific interaction with the opioid receptor. The anaesthetic-like membrane effect of 10 opioid agents and the antagonist naloxone was determined and correlated with their hydrophobicity. The inhibitory effect of drugs on protozoan motility was used as a measure of their membrane toxicity, measured by the reduction in swimming speed of Tetrahymena pyriformis using an image analysis system. Hydrophobicity was determined as the n-octanol/water partition coefficient, at pH 7.4, 37 degrees C. Opioid agents dose-dependently reduced the swimming speed of Tetrahymena pyriformis with a wide range of IC50 values. Some weak opioid agents were shown to have high protozoan immobilising potency comparable to quinidine, an agent with known membrane stabilising activity. Norpropoxyphene, the metabolite of dextropropoxyphene, with little affinity for the opioid receptor, also had a high potency. The inhibition of protozoan motility by these opioid agents was not antagonised by the opioid receptor antagonist naloxone; moreover an additive inhibitory action was demonstrated when opioid agents were combined with naloxone. The effect of opioid agents on protozoan motility was closely correlated with their partition coefficient but not with their known affinity for opioid receptors. These results suggest that opioid agents possess differing degrees of membrane depressant action independent from their interaction with the opioid receptor, and have a potential for causing depressant effects on excitable tissues.
Animals↗
The influence of pH on urinary ionized [Ca2+]: differences between urinary tract stone formers and normal subjects.
OBJECTIVE: To assess the role of pH in determining the solubility of Ca2+ in urine from normal subjects and stone formers and to determine the conditions which cause the formation of crystalline products. MATERIALS AND METHODS: Urine, collected from normal subjects and urinary tract stone-formers, was used in vitro. The concentration of ionized calcium, [Ca2+], and pH were measured with ion-selective electrodes and the formation of crystalline products measured as the change in turbidity of the specimen. The composition of the crystalline products was analysed by infrared spectroscopy. RESULTS: The [Ca2+] decreased with increasing pH and showed a biphasic relationship with a critical pH (pHn) at which Ca-containing precipitates appeared. Compared with normal subjects, the mean (SD) value of pHn was significantly lower in urine from stone-formers, at 7.67 (0.62) and 7.21 (0.54), respectively, and nearer to their voided pH of 5.92 (0.70) and 6.26 (0.71), respectively. The lower pHn in stone-formers could not be explained by altered concentrations or binding properties of Ca(2+)-binding ligands. pHn increased after diluting the urine and the value of pHn was strongly dependent on the [Ca2+] at a standardized pH. CONCLUSIONS: Crystalline precipitates appear in urine at a critical pH which is closer to the voided pH in stone-formers than in normal subjects and might explain the greater propensity of this group to form stones. The value of pHn is critically dependent on the urinary [Ca2+] and manoeuvres which reduced its concentration would reduce the tendency to form stones.
Binding Sites↗
Abnormal action potential conduction in isolated human hypertrophied left ventricular myocardium.
INTRODUCTION: Cardiac hypertrophy is associated with an increased incidence of arrhythmias that result from altered action potential configuration or propagation velocity. These variables were measured in isolated preparations of human left ventricular myocardium and correlated with the degree of hypertrophy. METHODS AND RESULTS: Cardiac mass was estimated by echocardiography and cell diameter was measured from fixed isolated specimens; the two variables correlated significantly. Action potential duration was measured under field stimulation but was independent of the degree of hypertrophy; however, the duration was longer in septal preparations (405 +/- 12 msec, 37 degrees C, 1-Hz stimulation) than in papillary muscles (342 +/- 11 msec). Conduction velocity decreased progressively as cell diameter increased both in septal and papillary muscle preparations. Cable analysis showed that the variation of conduction velocity could be accounted for adequately by an increase of the intracellular resistivity of the preparations. CONCLUSION: The data suggest that conduction defects occur in a progressive manner in human hypertrophy, which would provide an important substrate for dysrhythmias in human left ventricular hypertrophy and could result from a decrease of electrical coupling between adjacent myocardial cells.
Action Potentials↗
Intracellular pH and H+ buffering capacity in guinea-pigs with left ventricular hypertrophy induced by constriction of the thoracic aorta.
Intracellular pH (pHi) was measured in left ventricular myocytes from hearts hypertrophied by constriction of the thoracic aorta. There was a continuous relation between an increase in heart-to-body weight ratio and a decrease in pHi (mean +/- S.D., 7.06 +/- 0.18 pH units in control hearts vs. 6.87 +/- 0.17 pH units in hypertrophied hearts). Intracellular H+ buffering capacity (beta) increased as pHi fell, but the value of beta was independent of hypertrophy per se.
Ammonium Chloride↗
The mode of action of several opioids on cardiac muscle.
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.
Action Potentials↗
Changes in cell-to-cell electrical coupling associated with left ventricular hypertrophy.
The impedance to current flow in the intracellular compartment of guinea pig left ventricular myocardium was measured at 20 degrees C and 37 degrees C using tissue from hypertrophied hearts subjected to aortic constriction. Alternating current of varying frequency was passed longitudinally along myocardial preparations, which revealed two time constants: one attributed to the surface membrane at the ends of the preparation and a second lying in the intracellular pathway. The longitudinal impedance was quantitatively analyzed in terms of a parallel intracellular and extracellular pathway; the former had two series components, one attributable to the sarcoplasm and the other to the low-resistance junctions between adjacent cells. This interpretation was consistent (1) with control experiments using n-heptanol, which increased the component attributed to intercellular junctions but not sarcoplasmic resistivity, and (2) with suspensions of isolated myocytes, which yielded a similar value for the sarcoplasmic resistivity. Aortic constriction increased the heart weight-to-body weight ratio of experimental animals from a mean value of 3.10 +/- 0.28 to 5.05 +/- 0.83 g/kg after 50 days of constriction and 5.60 +/- 0.95 g/kg after 150 days of constriction. An increase of heart weight-to-body weight ratio at 150 days of constriction was associated with an increased intracellular resistivity, which could be attributed solely to an increase of the junctional resistance between adjacent cells by approximately 44% at 20 degrees C and 140% at 37 degrees C; the sarcoplasmic resistivity was unchanged. The results are discussed in terms of altered conduction in hypertrophied myocardium as a possible basis for arrhythmias in this tissue.
Alcohols↗
Initiation of contraction in detrusor smooth muscle.
Explore the source record for details and available documents.
Actins↗
Membrane action of chloramphenicol measured by protozoan motility inhibition.
The mechanism of the grey baby syndrome produced by chloramphenicol overdose is poorly understood. The present study assessed the membrane toxicity of this agent by means of its depressant effect on excitable tissues. The inhibition by drugs of protozoan motility was used as a toxicity endpoint, measured by the swimming speed of Tetrahymena pyriformis using an image analysis system. The n-octanol/water partition coefficient at pH 7.4, 37 degrees C was determined as a measure of the hydrophobicity of the drugs. Chloramphenicol dose-dependently depressed the motility of the test organism with an IC50 value (the concentration reducing the mean swimming speed to 50% of control) of 2.95 +/- 0.25 mM, in contrast to a significantly weaker effect of its succinate salt with an IC50 of 28.2 +/- 1.93 mM. Thiamphenicol, a drug with similar properties to chloramphenicol, produced little effect on protozoan motility. Several other antibiotics either in free or salt forms were also ineffective. A series of agents known to possess membrane stabilising action also tested for comparison showed that chloramphenicol possesses the ability to reduce protozoan motility. Measurement of the n-octanol/water partition coefficient revealed a value for chloramphenicol of 11.9 +/- 0.66. This property was correlated with protozoan immobilising potency among a series of heterogeneous compounds, suggesting that the mechanism involved a hydrophobic interaction with the excitable membrane. These results show that chloramphenicol has a depressant effect on protozoan motility comparable to agents with known toxicity effects on cell membranes. This suggests that chloramphenicol has the potential to cause membrane-mediated toxic effects, a mode of action that may underlie its acute toxicity to excitable tissues.
1-Octanol↗
The effects of cellular hypoxia on contraction and extracellular ion accumulation in isolated human detrusor smooth muscle.
PURPOSE: The effect of cellular hypoxia on the phasic isometric contraction of isolated preparations of human detrusor muscle was measured and the influence of the accumulation of extracellular H+ and K+ on the inotropic effects ascertained. MATERIAL AND METHODS: Strips of human detrusor smooth muscle were field stimulated and superfused with an HCO3-/CO2 medium. Cellular hypoxia was generated by superfusion with 1) a low PO2 (approximately 5 kPa) solution; 2) 5 mM. Na azide; or 3) 10 mM. 2-deoxyglucose and omission of glucose and Na pyruvate. Extracellular pH or [K+] was simultaneously measured with ion-selective microelectrodes placed in the muscle strip. RESULTS: Interventions produced a reversible contractile decay in the steady state, but the decay was preceded by a transient increase of force in most preparations. A small rise of the extracellular [K+] was also measured, but the effect was significantly smaller with 2-deoxyglucose. Extracellular acidosis was recorded with low PO2 and Na azide, but was absent with 2-deoxyglucose. The extracellular acidosis was usually preceded by a transient extracellular alkalosis. CONCLUSION: Part of the contractile changes under these conditions could result from an extracellular acidosis generated via glycolysis; the accumulation of extracellular K+ was insufficient to exert inotropic effects.
Azides↗
Differences in the free Ca2+ in undiluted urine from stone formers and normal subjects using a new generation of ion-selective electrodes.
OBJECTIVES: To measure the ionized Ca2+ in urine from normal subjects and patients with urinary tract stones. PATIENTS AND METHODS: Urine samples were obtained from 37 normal subjects and 52 stone-formers. Ca2+ was measured using plastic dip-cast ion-selective electrodes; total Ca and other variables were measured by standard analytical techniques. RESULTS: The ionized Ca2+ and the total Ca were greater in stone-formers' urine although the difference was more significant with the Ca2+ data, especially at a standardized pH. Absolute values of the Ca2+ were dependent on the type of reference electrode used. The Ca2+ was a function of urine pH; lower values were recorded as pH increased. Measured values of the Ca2+ did not correlate well with calculated values using a standard computer program. CONCLUSIONS: Measurement of the Ca2+ in spot urine samples at a standard pH provides a more discriminative test than total Ca for the presence of urinary tract stones. The pH dependence of the Ca2+ may have important consequences in the formation of urinary tract stones. The poor correlation between measured and computed values of Ca2+ emphasizes the importance of accurate measurement of this variable.
Calcium↗
Effect of pH on myofilament Ca(2+)-sensitivity in alpha-toxin permeabilized guinea pig detrusor muscle.
PURPOSE: To ascertain if the inotropic effects of altered intracellular pH on detrusor smooth muscle could be explained by a change in Ca(2+)-sensitivity of the contractile proteins. MATERIALS AND METHODS: Guinea pig detrusor smooth muscle was permeabilized with alpha-toxin and exposed to solutions mimicking the composition of the intracellular compartment and of varying [Ca2+]. Isometric tension was measured during exposure to solutions of varying [Ca2+] at pH 6.3, 7.1 and 7.5. RESULTS: At pH 7.1 the pCa (-log10[Ca2+]) required for half-maximal activation (pCa50) was 6.00 +/- 0.07 at 22C. A Hill coefficient of unity suggested lack of cooperativity in myofilament Ca2+ activation. A decrease of pH from 7.1 to 6.3 had no significant effect on the pCa50 value or the maximum Ca2+ activated force. An increase to pH 7.5 decreased the pCa50 value by 0.65 +/- 0.20 units but left maximum force unaffected. CONCLUSIONS: The reduced Ca2+ sensitivity of detrusor myofilaments at alkaline pH could partly explain the negative inotropic effect of intracellular alkalosis in intact muscle. The positive inotropic effect of intracellular acidosis cannot, however, be explained by alteration to myofilament Ca2+ sensitivity.
Actin Cytoskeleton↗
The electrophysiology of human detrusor smooth muscle.
Explore the source record for details and available documents.
Action Potentials↗
The actions of extracellular H+ on the electrophysiological properties of isolated human detrusor smooth muscle cells.
1. The influence of extracellular pH changes on intracellular pH and [Ca2+], as well as on L-type Ca2+ currents, has been investigated in isolated human detrusor smooth muscle cells. 2. Alteration of extracellular pH by changing superfusate PCO2 also changed intracellular pH. A change of superfusate pH made by altering the [NaHCO3] at constant PCO2 was not reflected in a change in intracellular pH. 3. Extracellular acidosis attenuated the magnitude and rate of change of intracellular [Ca2+] evoked by raising the extracellular [KCl]. 4. Extracellular acidosis attenuated the rate of rise and amplitude of the action potential, as well as the magnitude of the L-type Ca2+ current. In the pH range 6.78-7.62 no alteration to the voltage dependence of Ca2+ current activation or inactivation was recorded. 5. A close proportional relationship between tension generated by multicellular strips and the magnitude of peak inward Ca2+ current in isolated cells was noted over a wide range of the two variables using a number of interventions, including alteration to extracellular pH, [Ca2+] and [Mg2+]. 6. Extracellular acidosis attenuated the magnitude of caffeine-dependent intracellular Ca2+ transients and the resting [Ca2+]i between transients. Acidosis was without effect on the rise of [Ca2+]i induced by carbachol. 7. The results suggest that the negative inotropic effect of extracellular acidosis can be accounted for by attenuation of the L-type Ca2+ current. The results also imply that intracellular stores are influenced by transmembrane Ca2+ fluxes at rest and that such fluxes are also attenuated by extracellular H+.
Acidosis↗
Measurement of intracellular pH in isolated human detrusor smooth muscle cells.
Intracellular pH, pHi, was measured in isolated human detrusor smooth muscle cells by epifluorescence microscopy. The mean value was 7.07 +/- 0.19 when superfused with a CO2/HCO3- solution. Alteration of superfusate PCO2 also changed pHi whereas NaHCO3 changes were without effect, suggesting that the cell membrane is permeable to CO2 but impermeable to HCO3-. Nonbicarbonate H+ buffering power of the cell was calculated as 20.3 mequiv. x 1(-1) x pH unit-1. Addition of NH4Cl to the superfusate induced an alkalosis and, upon removal, a transient acidosis. The recovery from the acidosis allowed calculation of the acid extrusion rate from the cell. The rate was dependent on pHi and increased as the cell was more acid.
Ammonium Chloride↗
Alterations to the electrophysiology of isolated human detrusor smooth muscle cells in bladder disease.
The aim of the study was to investigate the properties of the inward calcium current (iCa) obtained from isolated human detrusor smooth muscle cells in different pathological conditions using the whole-cell patch-clamp technique. Previous experiments on field stimulated detrusor muscle strips have shown specific differences associated with hypertrophy and detrusor instability. As iCa plays an important role in excitation-contraction coupling in this tissue, it was therefore of interest to determine if iCa was altered in the above disease states. It was found that myocytes from patients with prostatic symptoms had a significantly increased surface area and that the kinetics of iCa were also significantly altered in these cells. Although the surface area of cells from patients with idiopathic instability and detrusor hyperreflexia was also significantly increased, the kinetics of iCa were altered in different ways. These alterations to iCa will alter the action potential configuration and its propagation through the muscle mass.
Action Potentials↗
Actions of extracellular chloride ion substitution on contractility of isolated ventricular myocardium.
OBJECTIVE: Replacement of extracellular chloride ions by some other anions exerts a positive inotropic effect on isolated cardiac muscle preparations. The aim of this study was to determine whether the increase of force was mediated by an intracellular alkalosis. METHODS: Isometric tension development was measured using guinea pig papillary muscles during replacement of superfusate Cl- with isethionate ions. Intracellular pH and L-type Ca2+ currents were measured in isolated myocytes using epifluorescence microscopy and a switch-clamp technique respectively. RESULTS: Reduction of extracellular Cl- increased tension, a phenomenon which was partially inhibited with the anion exchange blocker SITS. Force was also increased by reducing superfusate PCO2. Reduction of superfusate [Cl-] and PCO2 both produced concentration dependent intracellular alkalosis. The relationship between the changes to tension and intracellular pH was different when either the superfusate [Cl-] or PCO2 was reduced, less pronounced when the [Cl-] was reduced. An increase of the L-type Ca2+ current was produced in low [Cl-] solutions which could be attributed to the accompanying intracellular alkalosis. CONCLUSIONS: The positive inotropic effect of superfusate Cl- removal can only partially be explained by intracellular alkalosis. Other, as yet unknown, changes must determine the remainder of the inotropic response.
Animals↗