John A. S. McGuigan

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The apparent dissociation constants (Kapp) and total ligand concentrations ([Ligand]T) from extensive published and unpublished macroelectrode measurements for Mg2+/ATP, Mg2+/EDTA and Ca2+/EGTA buffers have been recalculated. These calculations were made feasible by the introduction of an Excel program which reduced the time of calculation for Kapp and(More)
Calibration of Ca(2+)/Mg(2+) macroelectrodes and flurochromes in the nmolar and mumolar range, respectively, require the use of buffer solutions. In these buffers the apparent dissociation constant (K(app)) has to be measured since calculation based on tabulated constants gives variable results. The ligand concentration [Ligand](T) has also to be estimated.(More)
An Papillarmuskeln von Rattenherzen ist bei Depolarisation mittels Spannungsklemme ein beträchtlicher Einwärtsstrom messbar, dessen Stärke in Na+-freier Lösung von der extrazellulären Ca2+-Konzentration abhängt. Die kurze Dauer des Aktionspotentials kleiner Nagetiere wird darauf zurückgeführt, dass die K+-Konduktivität bei Depolarisation der Zellmembran(More)
The new fluorescent indicator, mag-fura-5, was evaluated for its ability to measure accurately physiological changes in cytosolic free magnesium. The apparent dissociation constants (K d) of the fluorochrome for Mg2+, Mg2+/EGTA and Ca2+/EGTA solutions were 14.7 mM, 15.4 mM, and 1.8 mM respectively. The calculated difference in the fluorescence ratios and in(More)
Using simulated Ca2+ and Mg2+ buffers, methods proposed to measure both ligand purity and the apparent dissociation constant (Kapp) were investigated regarding (1) predicted accuracy of both parameters and (2) generality of the solution. The Bers' Ca2+ macroelectrode method [Bers, D. M., 1982 A simple method for the determination of free [Ca] in Ca-EGTA(More)
The modern view of the mammalian ventricular action potential is that Na-ions are responsible for depolarization, the plateau is maintained by an inward Ca current and repolarization is due to the inactivation of this inward Ca current against a background outward K current. The electrical activity spreads over the surface and T-tubules of the cell and the(More)
1. The effect of [K]0 on the current-voltage relationship is described. In the negative potential range the curves cross over as [K]0 is increased. At positive potentials the curves re-cross so that in low [K]0 there is more outward current than in high [K]0 2. Chord conductance has been calculated from the current-voltage relationship and this is taken as(More)
Many organic anions bind free Ca(2+), the total concentration of which must be adjusted in experimental solutions. Because published values for the apparent dissociation constant (Kapp) describing the Ca(2+) affinity of short chain fatty acids (SCFAs) and gluconate are highly variable, Ca(2+) electrodes coupled to either a 3M KCl or a Na(+) selective(More)
The ionized concentration of calcium in physiological buffers ([Ca(2+)]) is normally calculated using either tabulated constants or software programs. To investigate the accuracy of such calculations, the [Ca(2+)] in EGTA [ethylene glycol-bis(β-aminoethylether)-N,N,N|,N|-tetraacetic acid], BAPTA [1,2-bis(o-aminophenoxy) ethane-N,N,N|,N|-tetraacetic acid],(More)