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Biomedical subjects

A Tinker

Publications and source records attributed to A Tinker.

At least 19 recordsLinked to original sources
PubMed1995

Measuring the length of the pore of the sheep cardiac sarcoplasmic reticulum calcium-release channel using related trimethylammonium ions as molecular calipers.

After incorporation of purified sheep cardiac Ca(2+)-release channels into planar phospholipid bilayers, we have investigated the blocking effects of a series of monovalent (CH3-(CH2)n-1-N+(CH3)3) and divalent ((CH3)3N(+)-(CH2)n-N+(CH3)3) trimethylammonium derivatives under voltage clamp conditions. All the compounds tested produce voltage-dependent block from the cytoplasmic face of the channel. With divalent (Qn) derivatives the effective valence of block decreases with increasing chain length, reaching a plateau with a chain length of n > or = 7. No decline in effective valence is observed with the monovalent (Un) derivatives. A plausible interpretation of this phenomena suggests that for the 90% of the voltage drop measured, the increase in length following the addition of a CH2 in the chain spans 12.7% of the electrical field. Extrapolating this distance to include the remaining 10% suggests that the applied holding potential falls over a total distance of 10.4 A. In addition, at high positive holding potentials there is evidence for permeation of the trimethylammonium ions and a valency specific relief of block.

Animals↗
PubMed1995

Women's health.

Although women live longer than men, new evidence indicates women bear a disproportionately heavy burden of disease. The effect of disease on economic productivity of women in developing countries has been largely ignored. Infections are often causes of disease in women, including those that affect reproductive health. Although men and women usually experience similar rates of many diseases, rates of exposure and treatment vary between men and women. If untreated, factors adversely affecting women's health in one stage compound women's ill health in succeeding stages.

Abortion, Legal↗
PubMed1994

How does ryanodine modify ion handling in the sheep cardiac sarcoplasmic reticulum Ca(2+)-release channel?

Under appropriate conditions, the interaction of the plant alkaloid ryanodine with a single cardiac sarcoplasmic reticulum Ca(2+)-release channel results in a profound modification of both channel gating and conduction. On modification, the channel undergoes a dramatic increase in open probability and a change in single-channel conductance. In this paper we aim to provide a mechanistic framework for the interpretation of the altered conductance seen after ryanodine binding to the channel protein. To do this we have characterized single-channel conductance with representative members of three classes of permeant cation; group 1a monovalent cations, alkaline earth divalent cations, and organic monovalent cations. We have quantified the change in single-channel conductance induced by ryanodine and have expressed this as a fraction of conductance in the absence of ryanodine. Fractional conductance seen in symmetrical 210 mM solutions is not fixed but varies with the nature of the permeant cation. The group 1a monovalent cations (K+, Na+, Cs+, Li+) have values of fractional conductance in a narrow range (0.60-0.66). With divalent cations fractional conductance is considerably lower (Ba2+, 0.22 and Sr2+, 0.28), whereas values of fractional conductance vary considerably with the organic monovalent cations (ammonia 0.66, ethylamine 0.76, propanolamine 0.65, diethanolamine 0.92, diethylamine 1.2). To establish the mechanisms governing these differences, we have monitored the affinity of the conduction pathway for, and the relative permeability of, representative cations in the ryanodine-modified channel. These parameters have been compared with those obtained in previous studies from this laboratory using the channel in the absence of ryanodine and have been modeled by modifying our existing single-ion, four-barrier three-well rate theory model of conduction in the unmodified channel. Our findings indicate that the high affinity, essentially irreversible, interaction of ryanodine with the cardiac sarcoplasmic reticulum Ca(2+)-release channel produces a conformational alteration of the protein which results in modified ion handling. We suggest that, on modification, the affinity of the channel for the group 1a monovalent cations is increased while the relative permeability of this class of cations remains essentially unaltered. The affinity of the conduction pathway for the alkaline earth divalent cations is also increased, however the relative permeability of this class of cations is reduced compared to the unmodified channel. The influence of modification on the handling by the channel of the organic monovalent cations is determined by both the size and the nature of the cation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Charged local anesthetics block ionic conduction in the sheep cardiac sarcoplasmic reticulum calcium release channel.

We have examined the effect of the charged local anesthetics QX314, QX222, and Procaine on monovalent cation conduction in the Ca2+ release channel of the sheep cardiac sarcoplasmic reticulum. All three blockers only affect cation conductance when present at the cytoplasmic face of the channel. QX222 and Procaine act as voltage-dependent blockers. With 500 Hz filtering, this is manifest as a relatively smooth reduction in single-channel current amplitude most prominent at positive holding potentials. Quantitative analysis gives an effective valence of approximately 0.9 for both ions and Kb(0)s of 9.2 and 15.8 mM for QX222 and Procaine, respectively. Analysis of the concentration dependence of block suggests that QX222 is binding to a single site with a Km of 491 microM at a holding potential of 60 mV. The use of amplitude distribution analysis, with the data filtered at 1 to 2 kHz, reveals that the voltage and concentration dependence of QX222 block occurs largely because of changes in the blocker on rate. The addition of QX314 has a different effect, leading to the production of a substate with an amplitude of approximately one-third that of the control. The substate's occurrence is dependent on holding potential and QX314 concentration. Quantitative analysis reveals that the effect is highly voltage dependent, with a valence of approximately 1.5 caused by approximately equal changes in the on and off rates. Kinetic analysis of the concentration dependence of the substate occurrence reveals positive cooperativity with at least two QX314s binding to the conduction pathway, and this is largely accounted for by changes in the on rate. A paradoxical increase in the off rate at high positive holding potentials and with increasing QX314 concentration at 80 mV suggests the existence of a further QX314-dependent reaction that is both voltage and concentration dependent. The substate block is interpreted physically as a form of partial occlusion in the vestibule of the conduction pathway giving a reduction in single-channel current by electrostatic means.

Anesthetics, Local↗
PubMed1993

Using large organic cations to probe the nature of ryanodine modification in the sheep cardiac sarcoplasmic reticulum calcium release channel.

We have reported that the large impermeant organic cations tetrabutyl ammonium (TBA+), tetrapentyl ammonium, and the charged local anesthetic QX314 produce unique reduced conductance states in the purified sheep cardiac sarcoplasmic reticulum Ca2+ release channel when present at the cytoplasmic face of the channel. We have interpreted this as a form of partial occlusion by the blocking cation in wide vestibules of the conduction pathway. Following modification with ryanodine, which causes the channel to enter a reduced conductance state with long open dwell time, these cations block the receptor channel to a level that is indistinguishable from the closed state. The voltage dependence of TBA+'s interaction with the Ca2+ release channel is the same before and after ryanodine modification. The concentration dependence is different, in that the ryanodine-modified channel has one-third the affinity for TBA+, which is accounted for predominantly by changes in the TBA+ on rate. The data are compatible with a structural change in the vestibule of the conduction pathway consequent upon ryanodine binding that reduces the capture radius for blocking ion entry.

Animals↗
PubMed1993

Probing the structure of the conduction pathway of the sheep cardiac sarcoplasmic reticulum calcium-release channel with permeant and impermeant organic cations.

The sarcoplasmic reticulum Ca(2+)-release channel plays a central role in cardiac muscle function by providing a ligand-regulated pathway for the release of sequestered Ca2+ to initiate contraction following cell excitation. The efficiency of the channel as a Ca(2+)-release pathway will be influenced by both gating and conductance properties of the system. In the past we have investigated conduction and discrimination of inorganic mono- and divalent cations with the aim of describing the mechanisms governing ion handling in the channel (Tinker, A., A.R. G. Lindsay, and A.J. Williams. 1992. Journal of General Physiology. 100:495-517.). In the present study, we have used permeant and impermeant organic cations to provide additional information on structural features of the conduction pathway. The use of permeant organic cations in biological channels to explore structural motifs underlying selectivity has been an important tool for the electrophysiologist. We have examined the conduction properties of a series of monovalent organic cations of varying size in the purified sheep cardiac sarcoplasmic reticulum Ca(2+)-release channel. Relative permeability, determined from the reversal potential measured under bi-ionic conditions with 210-mM test cation at the cytoplasmic face of the channel and 210 mM K+ at the luminal, was related inversely to the minimum circular cation radius. The reversal potential was concentration-independent. The excluded area hypothesis, with and without a term for solute-wall friction, described the data well and gave a lower estimate for minimum pore radius of 3.3-3.5 A. Blocking studies with the impermeant charged derivative of triethylamine reveal that this narrowing occurs over the first 10-20% of the voltage drop when crossing from the lumen of the SR to the cytoplasm. Single-channel conductances were measured in symmetrical 210 mM salt. Factors other than relative permeability determine conductance as ions with similar relative permeability can have widely varying single-channel conductance. Permeant ions, such as the charged derivatives of trimethylamine and diethylmethylamine, can also inhibit K+ current. The reduction in relative conductance with increasing concentrations of these two ions at a holding potential of 60 mV was described by a rectangular hyperbola and revealed higher affinity binding for diethylmethylamine as compared to trimethylamine. It was possible to describe the complex permeation properties of these two ions using a single-ion four barrier, three binding site Eyring rate theory model. In conclusion, these studies reveal that the cardiac Ca(2+)-release channel has a selectivity filter of approximately 3.5-A radius located at the luminal face of the protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Review: abuse of elderly people in the domestic setting: a UK perspective.

Interest in, and concern about, the abuse of elderly people is growing rapidly. A study of the literature shows little research in the UK, but valuable indicators about risk factors and interventions from North America. One of the major problems has been definition and this paper distinguishes between different kinds of abuse. Conclusions are drawn about future research, and about the importance of records, assessment and multidisciplinary working, as well as the prevention of abuse.

Aged↗
PubMed1993

Cation conduction in the calcium release channel of the cardiac sarcoplasmic reticulum under physiological and pathophysiological conditions.

OBJECTIVE: The aim was to perform a theoretical and experimental study of the possible variations in Ca2+ current through the open cardiac sarcoplasmic reticular Ca2+ release channel under the ionic conditions associated with physiological and pathophysiological states. METHODS: The sheep cardiac sarcoplasmic reticular Ca2+ release channel was purified and reconstituted into planar phospholipid bilayers for study under voltage clamp conditions. Single channel current-voltage relationships were measured under putative physiological conditions with 1, 5, and 10 mM intraluminal Ca2+. The mathematics of a computer model based on Eyring rate theory were extended to include the interactions of three permeant ions. RESULTS: A model used previously to describe ionic conduction under simpler ionic conditions was able to predict the interaction of Ca2+, Mg2+, and K+ in the probable physiological range over the voltage range of interest. The predicted Ca2+ current under ionic conditions proposed to occur at the end of diastole is sensitive to relatively small changes in holding potential which suggests the need for adequate charge compensation across the sarcoplasmic reticular membrane. Theoretically, it was predicted that variations in intraluminal Ca2+, such as may occur in Ca2+ overload and other conditions, and variations in cytosolic Mg2+, which may occur in myocardial stunning, may significantly affect Ca2+ flux through the open Ca2+ release channel. CONCLUSIONS: Variations in permeant ion concentration such as may occur in physiological and pathophysiological states may significantly affect the quantity of Ca2+ released from the cardiac sarcoplasmic reticulum.

Animals↗
PubMed1992

Block of the sheep cardiac sarcoplasmic reticulum Ca(2+)-release channel by tetra-alkyl ammonium cations.

The purified ryanodine receptor channel of the sheep cardiac muscle sarcoplasmic reticulum (SR) membrane functions as a calcium-activated cation-selective channel under voltage-clamp conditions following reconstitution into planar phospholipid bilayers. We have investigated the effects of the tetra-alkyl ammonium (TAA) cations, (CnH2n+1)4N+ and the trimethyl ammonium cations, ethyltrimethyl ammonium and propyltrimethyl ammonium, on potassium conductance through the receptor channel. Small TAA cations (n = 1-3) and the trimethyl ammonium derivatives act as asymmetric, voltage-dependent blockers of potassium current. Quantitative analysis of the voltage dependence of block indicates that the conduction pathway of the sheep cardiac SR ryanodine receptor channel contains two distinct sites for the interaction of these small organic cations. Sites are located at approximately 50% for tetramethyl ammonium (TMA+) and 90% for tetraethyl ammonium (TEA+) and tetrapropyl ammonium (TPrA+) of the voltage drop across the channel from the cytosolic face of the protein. The chemical substitution of an ethyl or propyl group for one of the methyl groups in TMA+ increases the voltage dependence of block to a level similar to that of TEA+ and TPrA+. The zero-voltage dissociation constant (Kb(0)) falls with the increasing number of methyl and methylene groups for those blockers acting 90% of the way across the voltage drop. This is interpreted as suggesting a hydrophobic binding site at this point in the conduction pathway. The degree of block increases as the concentration of small TAA cations is raised. The concentration dependence of tetraethyl ammonium block indicates that the cation interacts with a single site within the conduction pathway with a Km of 9.8 +/- 1.7 mM (mean +/- SD) at 40 mV. Larger TAA cations (n = 4-5) do not induce voltage-dependent block of potassium current of the form seen with the smaller TAA cations. These data support the contention that the sheep cardiac SR ryanodine receptor channel may be occupied by at most one ion at a time and suggest that a large proportion of the voltage drop falls over a relatively wide region of the conduction pathway.

Animals↗
PubMed1992

Large tetraalkyl ammonium cations produce a reduced conductance state in the sheep cardiac sarcoplasmic reticulum Ca(2+)-release channel.

The purified Ca(2+)-release/ryanodine receptor channel of the sheep cardiac muscle sarcoplasmic reticulum (SR) functions as a calcium-activated cation-selective channel under voltage clamp conditions following reconstitution into planar phospholipid bilayers. We have investigated the effect of large tetraalkyl ammonium (TAA) cations, (CnH2n+1)4N+ (n = 4 and 5) on monovalent cation conduction. These cations modify the conductance of the receptor channel at positive holding potentials from the cytosolic side of the channel. Under these conditions, openings are resolved as a mixture of normal full amplitude events and events of reduced conductance. The amplitude of the reduced conductance state is a fixed proportion of the normal open state. As a proportion of all open events, the occurrence of the tetrabutyl ammonium (TBA+) related subconductance state increases with concentration and increasingly positive holding potential. The TBA+ related subconductance state displays similar conduction properties to the unmodified channel; with a linear current-voltage relationship, a similar affinity for K+ and voltage-dependent block by TEA+. A method was used to quantify the voltage dependence of the occurrence of the TBA+ effect, which yielded an effective gating charge of 1.66. A second method based on kinetic analysis of the voltage dependence of transitions between the full open state and the TBA+ related subconductance state produced a similar value. In addition, this analysis revealed that the bulk of the voltage-dependence resided in the off rate. TBA+ related subconductance events, expressed as a proportion of all open events, saturated with increasing TBA+ concentration. Kinetic analysis revealed that this could be entirely accounted for by changes in the on rate. Tetrapentyl ammonium (TPeA+) causes a qualitatively similar effect with a subconductance state of lower amplitude. The voltage-dependence of the effect was comparable to that displayed by TBA+. These findings are interpreted as a form of partial block in which more than one large TAA cation binds at the extremity of the voltage drop to produce an electrostatic barrier for ion translocation.

Animals↗
PubMed1992

Divalent cation conduction in the ryanodine receptor channel of sheep cardiac muscle sarcoplasmic reticulum.

The conduction properties of the alkaline earth divalent cations were determined in the purified sheep cardiac sarcoplasmic reticulum ryanodine receptor channel after reconstitution into planar phospholipid bilayers. Under bi-ionic conditions there was little difference in permeability among Ba2+, Ca2+, Sr2+, and Mg2+. However, there was a significant difference between the divalent cations and K+, with the divalent cations between 5.8- and 6.7-fold more permeant. Single-channel conductances were determined under symmetrical ionic conditions with 210 mM Ba2+ and Sr2+ and from the single-channel current-voltage relationship under bi-ionic conditions with 210 mM divalent cations and 210 mM K+. Single-channel conductance ranged from 202 pS for Ba2+ to 89 pS for Mg2+ and fell in the sequence Ba2+ greater than Sr2+ greater than Ca2+ greater than Mg2+. Near-maximal single-channel conductance is observed at concentrations as low as 2 mM Ba2+. Single-channel conductance and current measurements in mixtures of Ba(2+)-Mg2+ and Ba(2+)-Ca2+ reveal no anomalous behavior as the mole fraction of the ions is varied. The Ca(2+)-K+ reversal potential determined under bi-ionic conditions was independent of the absolute value of the ion concentrations. The data are compatible with the ryanodine receptor channel acting as a high conductance channel displaying moderate discrimination between divalent and monovalent cations. The channel behaves as though ion translocation occurs in single file with at most one ion able to occupy the conduction pathway at a time.

Animals↗
PubMed1992

A model for ionic conduction in the ryanodine receptor channel of sheep cardiac muscle sarcoplasmic reticulum.

A model is developed for ionic conduction in the sheep cardiac sarcoplasmic reticulum ryanodine receptor channel based on Eyring rate theory. A simple scheme is proposed founded on single-ion occupancy and an energy profile with four barriers and three binding sites. The model is able to quantitatively predict a large number of conduction properties of the purified and native receptor with monovalent and divalent cations as permeant species. It suggests that discrimination between divalent and monovalent cations is due to a high affinity central binding site and a process that favors the passage of divalent cations between binding sites. Furthermore, differences in conductance among the group Ia cations and among the alkaline earths are largely explained by differing affinity at this putative central binding site.

Animals↗
PubMed1991

Detection of interleukin-1 and interleukin-6 in adult rat brain, following mechanical injury, by in vivo microdialysis: evidence of a role for microglia in cytokine production.

In vivo levels of interleukin-1 (IL-1) and IL-6, present in the interstitial spaces of brain, have been repeatedly monitored up to 7 days after insertion of a microdialysis probe, designed to induce mechanical trauma to the brain. IL-1 is barely detectable immediately after implantation but over a 24-48 h period a 15-fold increase is seen. In contrast IL-6 levels at day 0 are high, increasing slightly (10%) by day 1 but decreasing to 40% by day 2. The temporal pattern of IL-6 recovery in the cerebrospinal fluid was similar to that in the dialysate but the levels were significantly lower and may reflect diffusion from the site of the probe lesion. Cellular sources of these cytokines include macrophages and neutrophils, which have infiltrated the lesion and microglia resident in the brain, which can be identified at the lesion site within 24 h of probe implantation. The astrocytic response to injury, evidenced by increased glial fibrillary acidic protein staining occurs much later, by day 7, and is unlikely to be responsible for IL-1 and IL-6 production found at 24-48 h. Since upon isolation and stimulation of microglia in vitro with lipopolysaccharide IL-1 and IL-6 can be measured in the supernatant, it would appear that they have the capacity to produce cytokines in vivo. Localised synthesis of cytokines at sites of brain injury by microglia would further stimulate microglia in an autocrine manner and also propagate the astrocytic reaction.

Animals↗
PubMed1990

Linkages between immunization and breastfeeding promotion programs.

Breastfeeding promotion and immunization are important interventions of child survival programs, especially in developing countries. Linkages between breastfeeding promotion programs and the Expanded Programme on Immunization (EPI) in developing countries mean that health care workers can make use of every contact with the mother and child to reinforce the educational messages of both programs. Breastfeeding does not interfere with vaccinations administered in accordance with the routine schedule recommended by the EPI Global Advisory Group for use in developing countries. Breastfeeding benefits the EPI and the EPI also benefits breastfeeding. The maximum reduction of morbidity and mortality will be achieved when all child survival interventions are applied in a balanced, complementary manner as envisaged in the concept of primary health care.

Breast Feeding↗
PubMed1989

Sulconazole nitrate 1% cream in the treatment of chronic moccasin-type tinea pedis caused by Trichophyton rubrum.

Sulconazole nitrate 1% cream applied twice daily was compared with its vehicle in the treatment of 229 patients with chronic moccasin-type tinea pedis confirmed by positive results of a potassium hydroxide preparation. At admission in this randomized, double-blind, parallel multicenter trial, 131 patients had positive dermatophyte cultures; Trichophyton rubrum was identified in 121 (92%). After 4 weeks of treatment, patients were examined and, if necessary, were treated for an additional 2 weeks. Sulconazole cream was significantly more effective than the vehicle in the treatment of chronic T. rubrum tinea pedis; 57% of patients were cured by sulconazole, compared with 13% cured with the vehicle. Relapse rates, assessed 2 weeks after the end of treatment, were significantly lower in patients treated with sulconazole than in those receiving vehicle (27% vs 71%). The 103 patients with moccasin-type tinea pedis whose cultures were not positive for T. rubrum achieved similar results.

Adolescent↗
PubMed1989

Severe pulmonary hypertension in Ullrich-Noonan syndrome.

A 19 year old woman with Ullrich-Noonan syndrome presented with a six month history of progressive dyspnoea and cyanosis. Clinical features were suggestive of severe pulmonary hypertension. Cross sectional echocardiography showed pronounced right ventricular pressure overload with right ventricular hypertrophy. Cardiac catheterisation confirmed severe pulmonary hypertension. Attempts to reduce pulmonary artery pressure with calcium channel blockers were unsuccessful. The patient died shortly after investigation. Necropsy confirmed primary pulmonary hypertension.

Adult↗
PubMed1989

Linkages between immunization and breastfeeding promotion programs.

Breastfeeding promotion and immunization are important interventions of child survival programs, especially in developing countries. Linkages between breastfeeding promotion programs and the Expanded Programme on Immunization (EPI) in developing countries mean that health care workers can make use of every contact with the mother and child to reinforce the educational messages of both programs. Breastfeeding does not interfere with vaccinations administered in accordance with the routine schedule recommended by the EPI Global Advisory Group for use in developing countries. Breastfeeding benefits the EPI and the EPI also benefits breastfeeding. The maximum reduction of morbidity and mortality will be achieved when all child survival interventions are applied in a balanced, complementary manner as envisaged in the concept of primary health care.

Breast Feeding↗