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C H Fry

Publications and source records attributed to C H Fry.

At least 73 records · Page 4Linked to original sources
PubMed1993

The regulation of intracellular Mg2+ in guinea-pig heart, studied with Mg(2+)-selective microelectrodes and fluorochromes.

Because of the reported presence of a Na(+)-Mg2+ exchanger in guinea-pig but not in ferret myocardium, the Mg2+ extrusion mechanism in guinea-pig myocardium has been reinvestigated using Mg(2+)- and Na(+)- selective microelectrodes and the fluorochromes mag-fura-2 and -5. The mean [Mg2+]i measured with microelectrodes in trabeculae or papillary muscles was 0.72 mmol/l (n = 22, thirteen experiments; range 0.42-1.23 mmol/l). Increasing [Mg2+]o from 0.5 mmol/l to either 10.5 or 20 mmol/l caused small increases in [Mg2+]i. Decreasing [Na+]o by 50% had no effect on the [Mg2+]i and there was no change in [Na+]i on increasing [Mg2+]o from 0.5 to 10.5 mmol/l. Varying pHo or changing pHi with NH4Cl did not influence the [Mg2+]i. In vitro calibration of mag-fura-2 and -5 using the ratio method gave values for K'd (experimentally determined dissociation constant) of 22.2 +/- 2.7 (mean +/- S.D., n = 7) and 25.7 +/- 1.3 (n = 4) mmol/l respectively. Mag-fura-2 reacted to physiological concentrations of Ca2+ and mag-fura-5 to changes in pH. In isolated myocytes, Na+ removal gave an apparent increase of [Mg2+]i with mag-fura-2 but not with mag-fura-5. However, when the pHi was altered with NH4Cl mag-fura-5 showed an apparent decrease in [Mg2+]i on application and an apparent increase on removal, with a time course similar to the pHi changes. It is concluded that Mg2+ extrusion in guinea-pig myocardium is not via a Na(+)-Mg2+ exchanger. The use of mag-fura-2 and -5 are limited in their application because of Ca2+ and H+ sensitivity respectively.

Animals↗
PubMed1993

Ionised magnesium and calcium in plasma from healthy volunteers and patients undergoing cardiopulmonary bypass.

OBJECTIVES: To measure the concentration of ionised magnesium, [Mg2+], and ionised calcium [Ca2+], in plasma from healthy volunteers and patients undergoing cardiopulmonary bypass (CPB). These measurements were carried out because there have been few reliable measurements of these values in healthy volunteers and no direct measurements in this patient group. PATIENTS AND METHODS: Dip cast ion selective electrodes were used to measure Mg2+, Ca2+, and H+ in plasma at 37 degrees C. These values were correlated with total metal concentrations, [Mg] and [Ca], plasma sodium [Na], and albumin concentrations found by standard techniques. Blood samples were taken from the patient group immediately before and after CPB and a further sample 24 hours later. RESULTS: In healthy volunteers the [Mg] was 0.86 (0.12) mM and [Mg2+], was 0.48 (0.06) mM, and the corresponding value for [Ca] was 2.34 (0.06) and for [Ca2+] 1.01 (0.13) mM. Values for [Mg], [Ca], and [Ca2+] have been reported by others and those quoted here are similar. In the CPB group the preoperative [Mg] was lower than the normal group but did not alter one hour after CPB and was slightly raised after 24 hours. The [Mg2+], however, was significantly reduced after 24 hours. Both [Ca] and [Ca2+] were slightly reduced after 24 hours but when adjusted for plasma albumin concentrations they were unchanged over this period. CONCLUSIONS: The most important finding is that around 24 hours after CPB the plasma [Mg2+] is significantly reduced, with no change to the total [Mg]. Corresponding changes to [Ca] and [Ca2+] were much smaller. This supposes the presence of an Mg2+ binding ligand of unknown origin in the plasma that may contribute to the cardiac arrhythmias that occur in some patients at this time after CPB.

Calcium↗
PubMed1992

The action potential and net membrane currents in isolated human detrusor smooth muscle cells.

The basic electrophysiological properties of the human detrusor have been investigated in vitro using isolated single cells obtained by collagenase digestion of bladder biopsy specimens. Recordings were made using the 'whole-cell patch clamp' technique using either a physiological filling solution or one in which cesium was used to block any outward current. Spontaneous and stimulated action potentials have been recorded and we have performed the first voltage clamp analysis of the currents that underlie the action potential in human detrusor. The depolarising phase of the action potential occurs by an inward current of Ca2+ ions which can be shown to be of sufficient magnitude to support the rate of upstroke. Repolarisation occurs due to an outward K+ current that is partially Ca2+ dependent. The techniques described here permit the investigation of the ionic basis for the control of contractility in the human bladder and may permit the characterisation of any underlying abnormality in the overactive detrusor.

Action Potentials↗
PubMed1992

Mechanical restitution of isolated human ventricular myocardium subjected to in vivo pressure and volume overload.

OBJECTIVE: The aim was to make a comparison of the mechanical and electrical refractory properties of isolated strips of human ventricular myocardium obtained from patients with either left ventricular pressure overload, volume overload, or normal left ventricular function. METHODS: Strips of ventricular myocardium were obtained at the time of cardiac surgery from 17 patients with aortic stenosis, representing pressure overload, 14 patients with aortic regurgitation, representing volume overload, and nine patients with mitral stenosis, representing normal left ventricular function. Muscle strips were mounted isometrically in a tissue bath, superfused with physiological saline at 37 degrees C, and stimulated at 1 Hz. Mechanical restitution curves were constructed from the isometric twitch tension obtained from extrastimuli during a special stimulus protocol. Transmembrane action potentials were recorded using glass microelectrodes and restitution of the upstroke velocity of action potentials studied in the presence of high external potassium concentration. RESULTS: The aortic stenosis group was older and had higher left ventricular systolic pressures and thicker left ventricular walls than the other groups. Electrocardiographic evidence of left ventricular hypertrophy was present in both the aortic stenosis and aortic regurgitation groups. Peak tension, time to peak tension, and the maximum rates of rise and fall of tension were not significantly different between groups. The time constant of the initial rapid recovery phase of mechanical restitution (tau 1) was prolonged in the aortic stenosis group, at 603(SEM 80) ms v 367(53) ms in the aortic regurgitation group (p < 0.005), and 259(70) ms in the mitral stenosis group (p < 0.005). There was a positive correlation between tau 1 and left ventricular wall thickness (p < 0.05). Neither "normal" nor "slow" (in the presence of raised external potassium) transmembrane action potentials differed in the groups studied. The mean time constant of recovery of "slow" action potential dV/dtmax was slower in the aortic stenosis group, but this difference was not significant. CONCLUSIONS: These data are consistent with the hypothesis that the rate of recovery of calcium release from the sarcoplasmic reticulum is slowed in myocardial hypertrophy due to pressure overload in man and provides a possible explanation of the occurrence of mechanical alternans in such patients.

Action Potentials↗
PubMed1992

The actions of extracellular magnesium on isolated human detrusor muscle function.

The effects of increasing the extracellular magnesium concentration ([Mg]) on the in vitro mechanical and electrophysiological properties of isolated human detrusor smooth muscle have been investigated. Raising extracellular Mg reduced the magnitude of the electrically-induced phasic contractions as well as spontaneous contractions. A similar increase in the [Mg] reduced the magnitude of the inward Ca2+ current associated with the action potential as well as shifting the activation curve to more positive potentials. Spontaneous oscillations of intracellular Ca2+ could be observed in some isolated cells and such activity was also abolished by raising the extracellular [Mg]. It is proposed that the contractile effects of raised extracellular Mg are mediated by an action on the inward Ca2+ current and that these observations suggest a means whereby normal and abnormal detrusor contractions might be effectively regulated.

Calcium↗
PubMed1992

Magnesium affects excitation, conduction, and contraction of isolated mammalian cardiac muscle.

An increase of extracellular Mg concentration, [Mg]o, reduced myocardial excitability and conduction without affecting the resting membrane potential or action potential configuration in ventricular myocytes and papillary muscles from a number of mammalian species. Although there was a small increase of specific membrane resistance and no change to intracellular resistivity, the threshold voltage was shifted to depolarized potentials. Thus loss of excitability can be explained by a shift of the activation of inward currents to depolarized potentials, and reduced conduction velocity is due solely to a diminution of local circuit currents. Mgo also was negatively inotropic, the magnitude of this effect being species dependent. Raised [Mg]o caused a small increase of intracellular [Mg] with a small decrease of intracellular [Na+], did not affect intracellular pH, and attenuated the intracellular Ca2+ transient associated with cell shortening in rat (but not rabbit) myocytes. An increase of [Mg]o reduced the magnitude of the voltage-dependent inward Ca2+ current, ICa, in rat and rabbit myocytes, and the activation curve of ICa was shifted to more depolarized potentials. A scheme to account for the negative inotropic effect of Mg is presented.

Animals↗
PubMed1991

Role of prostaglandins and leukotrienes in the synergistic effect of oxytocin and corticotropin-releasing hormone (CRH) on the contraction force in human gestational myometrium.

We have recently demonstrated that corticotropin releasing hormone (CRH) potentiates the contractile response to oxytocin of human gestational myometrium, using a high flow microsuperfusion system and electrical field stimulation. We now report this potentiation to be equivalent to that of 1 nM prostaglandin F2 alpha (PGF2 alpha), while 10 nM PGF2 alpha did not potentiate the response to oxytocin. Prostaglandin E2 (PGE2) also showed no augmentation of the contraction force of the myometrium in response to oxytocin. The CRH potentiated response was inhibited by the lipoxygenase and cyclooxygenase inhibitor BW755C (1 microM) and by indomethacin (0.1 microM), but not by the lipoxygenase inhibitor BW4C (1 microM). Measurements of prostaglandins in the superfusate showed no significant trends. It is concluded that the potentiation of contraction force to oxytocin by CRH is dependent on prostaglandins, probably PGF2 alpha and that leukotrienes, generated via the lipoxygenase pathway are not involved.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1991

The effects of pH changes on human and ferret detrusor muscle function.

1. The effects of altering extracellular pH on the electrically evoked contractions of ferret and human bladder (detrusor) smooth muscle have been investigated. pH was varied by changing superfusate PCO2 or NaHCO3 concentration. Acidosis increased force when superfusate PCO2 was raised but decreased force when the NaHCO3 concentration was reduced. 2. Intracellular pH (pHi) in isolated ferret detrusor cells was measured separately by epifluorescence microscopy. Extracellular pH changes caused by altering superfusate PCO2 were accompanied by similar changes of pHi, whereas variation of the NaHCO3 concentration had smaller effects on pHi. 3. It was proposed that intracellular acidosis increased contraction but extracellular acidosis depressed contraction. 4. Other interventions, such as addition and removal of NH4Cl, Cl- replacement, and NaHCO3 replacement with HEPES, changed pHi and had predictable effects on force. It was possible to describe unique relationships between tension and either intracellular or extracellular pH regardless of the means whereby pH changes were brought about. 5. Resting tension was reduced whether brought about by either intracellular or extracellular acidosis. K+ contractures were similarly affected by acidosis. Ferret preparations showed low levels of spontaneous activity, which was reduced by acidosis and enhanced by alkalosis.

Adult↗
PubMed1990

The influence of pH on Ca2+ exchange in ferret heart mitochondria.

The effect of pH changes on Ca2+ transport by isolated heart mitochondria was measured. Two components of Ca2+ transport were identified, an accumulation dependent on mitochondrial respiration and a Na+-dependent efflux. A decrease of pH over the range 7.7-6.7 reduced the initial rate and the total amount of respiration dependent Ca2+ accumulation. At pH 7.2 the [Na+] required to activate half-maximal efflux, k1/2, was 7.5 +/- 1.1 mM. Decreasing the pH over the range 7.7 to 6.9 increased the k1/2 from 3.6 to 11.6. The effect of acidosis was more profound on the respiration dependent Ca2+ uptake than the Na+-dependent efflux.

Animals↗
PubMed1990

Mechanical restitution in isolated mammalian myocardium: species differences and underlying mechanisms.

Ventricular myocardium was obtained from guinea-pig, ferret and human hearts. In each case small strips were mounted isometrically in a tissue bath and superfused with a physiological saline at 37 degrees C. The preparations were stimulated at 1 Hz and ectopic stimuli of different preceding intervals were given. The relationship between the force produced by the ectopic contraction and the duration of the preceding interval was plotted to form mechanical restitution curves (MRC). In the guinea-pig the MRC is described by a rapid recovery phase with an exponential time constant of 220 +/- 22.7 ms (mean +/- S.E.M.) followed by a decay (28.5 +/- 8.4 s). In ferret and man the rising phase is described by two exponentials (192.5 +/- 43.2 ms and 4.4 +/- 1.5 s in the ferret; 259.7 +/- 45.2 ms and 3.0 +/- 1.0 s in man). The decay phase is slower in ferret (22 +/- 156 s, P less than 0.02) and man (177 +/- 70 s, P less than 0.002) than in guinea-pig. There was no significant difference between the time constants of the rapid recovery phase of mechanical restitution in each species. The time constant of the rapid recovery phase (tau 1) was abbreviated by ryanodine, ouabain and adrenaline in human myocardium and by ryanodine alone in guinea-pig. Verapamil increased tau 1 in both species. The decay time constant (tau 3) was prolonged by ouabain, verapamil and by increasing extracellular [Ca2+] in human myocardium and by ouabain and verapamil in guinea-pig. The recovery of the second inward current in human myocardium was not correlated to the recovery of mechanical function. It is suggested that tau 1 is dependent on the recycling of Ca2+ within the cell as well as the reactivation of the second inward current. The decay phase, tau 3, is dependent on the rate of Ca2+ efflux from the cell, possibly via a Na+/Ca2+ exchange mechanism. The mechanisms underlying the slow recovery time constant, tau 2, are unclear but it is important to calculate tau 2 for the proper evaluation of tau 1.

Animals↗
PubMed1990

Effects of acid-base changes on human ureteric smooth muscle contractility.

Wide fluctuations of both urinary pH and the partial pressure of CO2 (PCO2) occur in normal physiological circumstances and in a variety of pathological conditions. However, the effect of extracellular pH on the contractility of human ureteric muscle has not been clearly defined. This study has established, using a microsuperfusion technique, that an increased superfusate PCO2 increases the magnitude of the phasic contraction to electrical field stimulation. A similar extracellular acidosis induced by alteration of the [HCO3-], at constant [Na+] and free [Ca2+], was without significant effect. Furthermore, when both superfusate PCO2 and [HCO3-] were simultaneously increased at constant pH the contractile response was similar to that when PCO2 alone was raised. These observations suggest that the changes of tension were mediated by intracellular pH changes, providing it is assumed that the ureteric smooth muscle cell membrane is permeable to CO2 but impermeable to H+ and HCO3-. The occurrence of an increase of force in the presence of an acidosis is a highly significant and unusual finding, since it has been assumed that the classical association between acidosis and negative inotropy, seen in cardiac muscle, was also applicable to smooth muscle.

Acid-Base Equilibrium↗
PubMed1990

Analysis and presentation of intracellular measurements obtained with ion-selective microelectrodes.

We have considered the manner in which data obtained with ion-selective electrodes should be evaluated. The potential difference recorded by such electrodes, with respect to a stable reference, is converted to a concentration by a non-linear transformation--the Nernst or Nikolsky equation. The mean and standard deviation of such estimations of concentration are then usually presented, which assumes that the latter variable is normally distributed. If, however, the recorded potential difference (PD) is the normally distributed variable and the mean value calculated, then a different value of mean concentration will be obtained. We show here that the recorded PD is indeed the normally distributed variable using data from a variety of ion-selective electrode measurements and conclude that the mean values of quoted ion concentrations have been overestimated by 6-43%.

Animals↗
PubMed1989

The contribution of mitochondrial calcium ion exchange to relaxation of tension in cardiac muscle.

The possible contribution of mitochondrial Ca2+ accumulation and release to contractile phenomena has been investigated. Two intracellular fractions of Ca2+ sequestration can be identified in cardiac myocytes, one ascribed to mitochondria. Two modes of Ca2+ transport exist within the mitochondrial fraction, one dependent upon mitochondrial respiration and the other upon extramitochondrial [Na+]. Experiments with trabeculae show that under appropriate conditions, the rate of relaxation and the amount of tension developed is dependent on these two modes of Ca2+ transport. A model is presented quantifying the contribution of the mitochondria to relaxation.

Animals↗
PubMed1989

Non-mitochondrial calcium ion regulation in rat ventricular myocytes.

Ca2+ exchange has been measured in a suspension of rat ventricular myocytes treated with digitonin or saponin to render the sarcolemma permeable to small molecules and ions. Two fractions of exchange were identified, one that was attributed to the mitochondrial component of the cell and the other to a non-mitochondrial fraction. Mitochondrial Ca2+ uptake was blocked by sodium azide and depended on respiratory substrates whereas non-mitochondrial uptake occurred independently of these molecules but was dependent on ATP and creatine phosphate. Non-mitochondrial Ca2+ uptake could be induced at a Ca2+ concentration below 1 microM and the initial rate increased with concentration up to 100 microM. Uptake could be reversed by sulmazole (a caffeine-like substance) and this reversal in turn inhibited by ryanodine. These properties suggest that the major locus for non-mitochondrial Ca2+ exchange is at the sarcoplasmic reticulum. Ca2+ exchange could be modulated by a number of agents, including carnosine, but was unaffected by others, including Na+, inositol trisphosphate and cyclic AMP. A kinetic model of the data is presented, which incorporates similar data of Ca2+ uptake into the mitochondrial fraction. The rates of Ca2+ exchange measured in these experiments suggest that these two components of the cell can reduce the sarcoplasmic Ca2+ concentration rapidly enough to account for the observed transient nature of the isometric twitch. Furthermore, it is suggested that both non-mitochondrial and mitochondrial fractions of the cell could significantly contribute to tension relaxation in rat cardiac muscle.

Animals↗
PubMed1988

The action of the prostaglandins on isolated human ureteric smooth muscle.

A study has been carried out on the actions of the prostaglandins E2 and F2 alpha and their synthesis inhibitors, indomethacin and diclofenac sodium, upon isolated human ureteric smooth muscle, using the technique of microsuperfusion designed to ensure good tissue viability. Indomethacin and diclofenac sodium were shown to abolish almost completely the contractile response of ureteric muscle to electrical field stimulation. Contractile activity, in the presence of the inhibitors, could be restored by prostaglandin E2 or F2 alpha or by increasing the external potassium concentration, [K+]O, of the superfusate. Prostaglandin E2 or F2 alpha alone were shown to increase dramatically both the phasic and tonic component of the electrically stimulated contractions, on occasions inducing spontaneous activity. A possible mechanism of action was elucidated with an electrophysiological technique using intracellular microelectrodes. The mean membrane potential recorded was 54.7 mV (SD +/- 10 mV, n = 15). The depolarising action of raising [K+]O was demonstrated and prostaglandin F2 alpha (3 x 10(-6) M) was shown to produce a small depolarisation of the ureteric muscle cell membrane.

Diclofenac↗
PubMed1987

The effects of cyanide on intracellular ionic exchange in ferret and rat ventricular myocardium.

The effects of cyanide on Ca2+ exchange in isolated ventricular myocytes and on the intracellular concentrations of Ca2+, Na+ and H+ have been investigated to assess the contribution that mitochondria might play in cellular Ca2+ metabolism. Ionic levels were measured with ion-selective electrodes. KCN (2.5 mM) inhibited a component of Ca2+ exchange in myocytes that could be attributed to mitochondrial exchange, but was without effect on non-mitochondrial Ca2+ exchange. NaCN (2.5 mM) caused a transient reduction of [H+]i, [Na+]i and [Ca2+]i when applied to the superfusate bathing ventricular trabeculae or papillary muscles. The transient changes of [Na+]i were accentuated when the preparation was exposed to a solution which would be expected to increase the cellular calcium content. The reduction of [Na+]i which accompanies a reduction of the extracellular sodium concentration, [Na]o, was attenuated in the presence of NaCN, but the intracellular acidosis resulting from a reduction of [Na]o was unaffected by NaCN. A small, but significant, rise of [Ca2+]i accompanied a reduction of [Na]o but only when NaCN was present in the superfusate. It is concluded that cyanide ions have a reasonably specific action on cardiac cellular ionic metabolism. Its primary action is to prevent mitochondrial Ca2+ sequestration. It is postulated that a Na+/H+ exchange, possibly at the sarcolemma, could account for some of the changes to sarcoplasmic ionic levels observed. In a solution of low [Na]o, it is concluded that mitochondria could sequester at least 30% of the calcium accumulated by the cell even though the sarcoplasmic [Ca2+] does not exceed 0.3 microM.

Animals↗
PubMed1987

The ionic basis of the anti-ischemic and anti-arrhythmic properties of magnesium in the heart.

The role of magnesium (Mg) in the prevention of ischemia-induced injury during cardioplegic arrest and in the treatment of cardiac arrhythmias has been considered. Although Mg possesses negative inotropic properties, potassium (K) is more effective than Mg in inducing cardiac arrest. The rationale for the inclusion of Mg in cardioplegic solutions therefore lies not in its cardioplegic properties, but in its ability to influence other cellular events such as the loss of Mg and K and perhaps to counter the detrimental effects of ischemia by antagonizing calcium (Ca) overload. Most of the Mg in the cardiac cell is complexed with high energy phosphate compounds and the loss of Mg during ischemia may restrict the repletion of ATP upon reperfusion and so impair the return of normal contractile function. The ability of Mg to limit K efflux from the cell is of importance not only in the prevention of ischemia-induced K loss but also in the treatment of digitalis-induced arrhythmias. Elevation of extracellular Mg has been shown to reduce the intracellular sodium ion activity ([Na]i) and this decline in [Na]i can be related to the negative inotropic properties of Mg. Mg may therefore exert some of its antiarrhythmic and antiischemic effects by limiting [Na]i-stimulated Ca influx (or facilitating Ca efflux) and hence preventing cellular Ca overload.

Animals↗