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Biomedical subjects

I Findlay

Publications and source records attributed to I Findlay.

At least 37 records · Page 2Linked to original sources
PubMed1994

Interactive regulation of the ATP-sensitive potassium channel of cardiac muscle.

A variety of ligands, including intracellular nucleotides, pharmaceutical products, and neurohormones, influence the adenosine triphosphate (ATP)-sensitive potassium channel of cardiac muscle. In this review it is emphasized that these ligands act not only on the channel-gating mechanism but also influence each others' effects or effectiveness in a quite complex series of interactions. Thus, ATP, which directly closes the channel-gating mechanism, also enhances the efficacy of sulfonylurea drugs and is necessary for the action of certain potassium-channel-opening drugs and neurohormones. Intracellular nucleoside diphosphates that, depending on the conditions, either act on the channel-gating mechanism or influence the effectiveness of ATP, also facilitate and reduce the effectiveness of potassium-channel opening and sulfonylurea drugs, respectively. Our knowledge of the mechanisms that underlie the interactions between these different ligands is limited. The cloning of the channel and the characterization of the different ligand-binding sites will be a great step forward.

Adenosine↗
PubMed1993

Molecular cloning, functional expression and localization of an inward rectifier potassium channel in the mouse brain.

We have cloned an inward-rectifier potassium channel from a mouse brain cDNA library, studied its distribution in the brain by in situ hybridization and determined the chromosomal localization of the gene. A mouse brain cDNA library was screened using a fragment of the mouse macrophage IRK1 cDNA as a probe. Two duplicate clones of approximately 5.5 kb were obtained. Xenopus ococytes injected with cRNA derived from the clone expressed a potassium channel with inwardly rectifying channel characteristics. The amino acid sequence of the clone was identical to that of IRK1 recently cloned from a mouse macrophage cell line. In situ hybridization study showed the mouse brain IRK1 to be generally distributed throughout the brain, but in particular subsets of neurons at high levels. The gene was placed in the distal region of mouse chromosome 11, which contains several uncloned neurological mutations. These results provide the first demonstration of the cloning and distribution of an inward rectifier potassium channel from the nervous system.

Animals↗
PubMed1993

YM934, a novel K+ channel opener, activates ATP-sensitive K+ channels in cardiac myocytes.

2-(3,4-Dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl)pyridin e N-oxide (YM934) is a newly synthesized benzoxazin. The effects of YM934 on ATP-sensitive K+ (KATP) channels in guinea pig cardiac ventricular myocytes and in an insulin-secreting cell line, HIT T15 beta-cells, were examined using the gigaohm-seal patch-clamp techniques. Under the whole-cell clamp condition, YM934 induced in ventricular myocytes a time-independent, glibenclamide-sensitive K+ current in a concentration-dependent fashion (EC50 = approximately 3 microM). On formation of inside-out patches in ATP-free solution, the KATP channel current abruptly appeared and then ran down. YM934 was applied to inside-out patches before, during and after channel "run-down." Because nucleoside diphosphates, such as uridine diphosphate (UDP), can induce channel openings after complete run-down, the effects of YM934 on the UDP-induced channel openings were also examined. Before run-down, YM934 enhanced KATP channel activity by decreasing the sensitivity of channels to intracellular ATP. YM934 also enhanced the partially run-down channel, even in the absence of ATP. After run-down, YM934 had no effect but could enhance the UDP-induced KATP channel openings. These effects of YM934 on cardiac KATP channels were similar to those of pinacidil and lemakalim. In HIT T15 beta-cells, 100 microM YM934 was ineffective in both cell-attached and inside-out patch configurations, suggesting the tissue-specific nature of the action of this novel K+ channel opener.

Adenosine Triphosphate↗
PubMed1993

Sulphonylurea drugs no longer inhibit ATP-sensitive K+ channels during metabolic stress in cardiac muscle.

The effects of the sulphonlyurea drugs glibenclamide and tolbutamide were tested upon ATP-sensitive K+ channels activated by dinitrophenol or carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone (FCCP) in ventricular myocytes isolated from rat hearts. In whole-cell current recording, 1 microM glibenclamide or 1 mM tolbutamide totally but only transiently inhibited the K+ current activated by dinitrophenol or FCCP. In cell-attached membrane patches, 1 to 100 microM glibenclamide initially inhibited the activation of ATP-sensitive K+ channels induced by dinitrophenol or FCCP, but failed to prevent the activation of these channels during contracture. Myocyte contracture induced by caffeine or Ca++ entry during K+ depolarization did not activate ATP-sensitive K+ channels. In excised membrane patches, 1 to 10 microM glibenclamide did not block completely opening of ATP-sensitive K+ channels. Neither intracellular ADP nor phosphorylable substrate were able to reliably influence the effect of glibenclamide. It is concluded that sulphonylurea drugs, otherwise highly effective blockers of this type of ion channel, were no longer able to inhibit the opening of ATP-sensitive K+ channels during the final stages of metabolic stress. These channels could therefore be responsible for both the glibenclamide-sensitive and glibenclamide-insensitive phases of K+ loss during cardiac ischemia.

Adenosine Triphosphate↗
PubMed1992

Preimplantation diagnosis of a human beta-globin transgene in biopsied trophectoderm cells and blastomeres of the mouse embryo.

The preimplantation diagnosis of a HbSA-globin transgene in biopsied trophectoderm cells and blastomeres in embryos using a transgenic mouse model for the trait of human sickle-cell anaemia has been undertaken. A sensitive procedure was developed for the amplification of the human beta-globin gene sequence flanking the sickle mutation. Polymerase chain reaction (PCR) assays were undertaken on one to five biopsied trophectoderm cells and isolated blastomeres of the preimplantation mouse embryo. After biopsy the blastocysts were cultured whilst the cells were analysed for the presence of the transgene, and a high proportion (82-91%) were viable as assessed by the presence of a blastocoele cavity within a 5-h period. The majority of the biopsied cultured blastocysts were frozen and used to confirm the diagnosis; 90 biopsied cultured blastocysts were transferred to pseudopregnant recipients and 34% established pregnancy. Material from day 13.5 post-coitum fetuses was also used to confirm the original diagnosis. The time (4-5 h) required to carry out the analysis obviates a need for extended culture or cryopreservation of the biopsied embryo. In individual experiments under optimal conditions, the presence of the transgene in biopsied cells was detected with 100% accuracy, and the PCR analysis was sensitive at the 1-cell level. The overall success rate of diagnosis and confirmation of the presence or absence of the human beta-globin sequence in the biopsied embryo was 70%. Over the entire experimental period (14 months) DNA contamination from a variety of sources did occasionally occur; the methods used to overcome this problem are discussed.

Anemia, Sickle Cell↗
PubMed1992

An interactive videodisc 'cancer patients and their families at home', designed for education in primary health care.

This article describes the development of an interactive videodisc program to support professional education in the field of cancer for the primary health care team. Based on a survey of needs, it concentrates on common symptoms and their control, and problems in communication. The educational approach adopted was chosen on the basis of an extensive consideration of the needs, and what was felt most appropriate for adult learners. Plans were carefully reviewed at each stage, with external advisers, and the prototype system independently evaluated in four sites before completing the package. With financial backing from the 'Europe against Cancer' initiative of the European Commission, and close cooperation with national practitioners, Dutch, German, Greek and Portuguese versions of the package have been developed. Local differences in practice are taken into account and translations of key aspects are provided.

Home Care Services↗
PubMed1992

Inhibition of ATP-sensitive K+ channels in cardiac muscle by the sulphonylurea drug glibenclamide.

The effects of the sulphonylurea drug glibenclamide were tested upon ATP-sensitive K+ (KATP) channels activated by 20 microM SR 44866 in isolated ventricular myocytes from guinea pig hearts. Glibenclamide inhibited the openings of KATP channels in both cell-attached and excised inside-out membrane patches. Glibenclamide inhibited the whole-cell KATP current (I-KATP) with an EC50 of 6 nM and Hill Coefficient of 1.26. The kinetics of the onset of inhibition of I-KATP were complex and dose-dependent. The recovery of I-KATP from inhibition was largely dose-independent. The application of glibenclamide for short periods of time was followed by the continued development of inhibition. These results suggest that the cell was loaded with the drug before it interacted with the KATP channel. It is proposed that the sulphonylurea receptor site is to be found in the lipid phase of the membrane. In consequence critical factors involved in the sulphonylurea drug-induced inhibition of KATP channels will include the rates of drug absorption into and exit from the membrane lipid. That sulphonylureas will be concentrated in the membrane lipid suggests that the EC50 value for channel inhibition does not represent the true affinity of the drugs for their receptor.

Adenosine Triphosphate↗
PubMed1992

Effects of pH upon the inhibition by sulphonylurea drugs of ATP-sensitive K+ channels in cardiac muscle.

The effect of pH was tested upon the inhibition of ATP-sensitive K+ (KATP) channels caused by the sulphonylurea drugs tolbutamide and glibenclamide. KATP channels and currents (I-KATP) were activated with SR 44866 in ventricular myocytes isolated from guinea pig hearts. Modification of either external or internal pH had little effect upon the background K+ current (IK1). External pH had no consistent effects upon I-KATP. The application of NH4Cl inhibited I-KATP and its withdrawal caused a slight rebound activation. Compared with the results obtained at pHo 7.4, inhibition of I-KATP by the sulphonylurea drugs was enhanced at pHo 6.5 and reduced at pHo 8.4. The kinetics of the recovery of I-KATP was independent of pHo. Neither internal pH 6.5 nor NH4Cl had any effect upon sulphonylurea-induced inhibition of I-KATP. The dose-response curves for inhibition of I-KATP at different pHo's were found to coincide when plotted for the unionized concentrations of the drugs. It is concluded that it is the unionized forms of the sulphonylurea drugs which are responsible for closure of KATP channels in cardiac muscle. In consequence, extracellular acidification during ischemia will increase the effective concentration of glibenclamide and may be responsible for the cardiovascular disorders associated with this treatment in noninsulin-dependent diabetics.

Adenosine Triphosphate↗
PubMed1991

ATP-sensitive K channels in heart muscle. Spare channels.

We show that ATP-sensitive K+ channels of excised inside-out membrane patches of rat ventricular myocytes show considerable variation in their sensitivity to ATP. In 102 different membrane patches IC50 values ranged from 9 to 580 microM ATP and Hill coefficients from 1% to 6.41% of patches showed openings of ATP-sensitive K+ channels in the presence of 1 mM ATP. These results considerably widen the range of internal ATP concentrations over which one might expect activation of the ATP-sensitive K+ current in cardiac myocytes.

Adenosine Triphosphate↗
PubMed1991

Activation of ATP-sensitive K channels by a K channel opener (SR 44866) and the effect upon electrical and mechanical activity of frog skeletal muscle.

To examine the effects of the activation of adenosine 5'-triphosphate (ATP)-sensitive K channels in a skeletal muscle we have applied the ATP-sensitive K channel opener SR44866 whilst recording single ion channels, voltage-clamped membrane currents, evoked action potentials and tension in sartorius muscles of the frog. In excised inside-out membrane patches SR44866 opened channels which could be inhibited by internal ATP and glibenclamide. In voltage-clamped individual muscle fibres SR44866 evoked a glibenclamide-sensitive membrane current which reversed at -70 mV. The effect of SR44866 was dose dependent with an effective concentration for 50% maximal effect (EC50) of 67 microM and a slope factor of 2. SR44866 dose dependently reduced the duration of the spike after-potential, spike overshoot, Vmax, tetrodotoxin-sensitive voltage-gated inward membrane currents and muscle twitch tension. From this evidence it can be concluded that the opening of ATP-sensitive K channels may be associated with the inhibition of contraction of skeletal muscle.

Action Potentials↗
PubMed1991

In-vitro studies on 'spare' human preimplantation embryos in culture.

Methods previously used for the biopsy of preimplantation mouse embryos have been applied to individual 'spare' human embryos. Early cleavage-stage human embryos have been cultured and individual blastomeres removed following zonae thinning or drilling. Embryos have also been cultured to the blastocyst stage for the biopsy of three to five trophectoderm cells. Both the biopsied embryo and the biopsied cells have been allowed to develop and/or grow in vitro.

Animals↗
PubMed1990

Action potential duration and activation of ATP-sensitive potassium current in isolated guinea-pig ventricular myocytes.

It is difficult to associate the ATP-sensitive potassium (K-ATP) channel of cardiac muscle with hypoxia/ischemia induced action potential shortening because this occurs before intracellular ATP falls to levels associated in vitro with channel opening. This leaves the cardiac K-ATP channel without any obvious physiological function. We have quantitatively examined the relationship between action potential duration and K-ATP channel activity in enzymatically isolated ventricular myocytes of the guinea-pig. In whole-cell voltage-clamp recording experiments when the K-ATP channel opener SR 44866 (2-10 microM) stimulated an outward membrane current greater than 50 pA at 0 mV membrane potential (the equivalent of 30 open K-ATP channels or 1% of the cell K-ATP channel population) action potential duration was reduced by more than 50%. In the majority of cell-attached membrane patch recordings metabolic inhibition stimulated K-ATP channel open probability of 1-2% which continued for long periods (7-25 min) before cell contracture and coincident major K-ATP channel activation (open probability 65%). Our quantitative analysis thus shows that physiologically relevant activity of K-ATP channels in cardiac muscle is confined to a very small percentage of the possible cell K-ATP current and thus intracellular ATP would not have to fall very far before the opening of K-ATP channels would influence cardiac excitability.

Adenosine Triphosphate↗
PubMed1990

Improvement of the culture conditions for the development of human preimplantation embryos.

The culture of human preimplantation embryos from the 1-cell to the morula/blastocyst stage of development is not satisfactory at present. The success of various IVF laboratories ranges from 18 to 23%, therefore there is a requirement for improvement in the standard conditions used to culture the embryo. Using a limited number of 'spare' human embryos which were donated for research, in-vitro studies have been undertaken using various culture media. The results show that a significant improvement in viability is achieved using Ham's F-12 medium compared with other media presently used for culturing embryos.

Culture Media↗
PubMed1990

[Decrease of the contraction force of skeletal muscle in mammals by the potassium channel activator, SR 44866].

The ATP-sensitive K channel opener, SR 44866, was applied to intact extensor digitorum muscle of the mouse. Electrically stimulated maximal twitch contractions of the muscle were decreased by SR 44866 with a KD of 7.4 microM and a Hill coefficient of 1.2 at 34 degrees C. The effect of SR 44866 was antagonized by glibenclamide and reduced at 24 degrees C. We suggest that these results represent the consequence of activation of ATP-sensitive K channels in mammalian skeletal muscle.

Adenosine Triphosphate↗