George G. McDonald

A new method for measuring longitudinal relaxation times

The longitudinal relaxation times of two-tryptophan protons were determined by using a new pulse sequence: apply a 90° pulse, spoil field homogeneity, wait for a delay time, τ, apply a 90° sampling pulse. Relaxation times of 1.6 and 3.0 seconds were found for the low and high field aromatic doublets of tryptophan using this new pulse sequence. On the basis of the relaxation times an assignment of the low and high field aromatic doublets to the C4 and C7 ring protons is made.

Interaction of general anesthetics with phospholipid vesicles and biological membranes

Low concentrations of general anesthetics, including halothane, ethrane, trilene, diethyl ether and chloroform are observed to shift the phase transitions of phospholipid vesicles to lower temperatures, and from these data partition coefficients for the anesthetic between lipid and water can be calculated. In contrast to the anesthetics, high concentrations of ethanol are required to shift the phase transition of lipids and glycerol causes no effect. Above the phase transition general anesthetics alter nuclear magnetic resonance spectra of phospholipid dispersions and increase the rotational and lateral diffusion rates of fluorescent probes located in the hydrocarbon core of the bilayer, indicating that they induce disorder in the structure. In red blood cell membranes and sarcoplasmic reticulum fragments, the rotational diffusion rate of 1-phenyl-6-phenylhexatriene is increased in the presence of general anesthetics. The 220 MHz nuclear magnetic resonance spectra of sarcoplasmic reticulum reveal some resolved lines from the lecithin fatty acid protons; addition of general anesthetic increases the contribution of these peaks. The data from the NMR and fluorescence techniques lead to the conclusion that general anesthetics increase the pool size of melted lipids in the bimolecular phospholipid layers of biological membranes; this would account for the ability of general anesthetics to increase passive diffusion rates of various substances in membranes.

Measurement of the self-diffusion coefficient of each component in a complex system using pulsed-gradient fourier transform NMR☆

Abstract The self-diffusion coefficient of each component in a multicomponent system may be determined by obtaining the Fourier transform of the spin echo using the pulsed gradient, spin echo technique. The pulsed gradient Fourier transform technique also has the individual advantages of Fourier transform NMR and the pulsed gradient technique leading to enhanced signal-to-noise ratio and improved resolution. The method is illustrated for a water(dimethylsulfoxide solution.

Measurement of transmembrane pH gradients in human erythrocytes using 19F NMR

Abstract A new high-sensitivity method has been described for measuring transmembrane pH gradients in vesicular systems using 19 F NMR. The 19 F resonance of trifluoroethylamine has been shown to have a large pH-dependent chemical shift and the position of the resonance was measured with high precision and sensitivity. In suspensions of human erythrocytes, trifluoroethylamine distributed itself across the membrane and separate 19 F resonances were obtained from the trifluoroethylamine inside and outside of the cells. The pH in each compartment was calculated from the resonance positions.

The relationship between global myocardial ischemia, left ventricular function, myocardial redox state, and high energy phosphate profile. A phosphorous-31 nuclear magnetic resonance study☆

UNLABELLED The onset of global myocardial ischemia was related to mechanical function (intraventricular pressure), cellular redox state (NADH fluorophotography), and high energy profile (phosphorous-31 nuclear magnetic resonance). Ten rabbit hearts were excised and perfused on a modified Langendorff apparatus (37 degrees C; pO2 480 Torr). Developed pressure and positive and negative dp/dt were determined at control, 1-10, 15, 30, 45, and 60 sec of acute global ischemia. NADH fluorophotographs were taken at control, 1-10, 15, 20, 30, 60 sec, and 5, 10, and 30 min. P-31 NMR spectra in 14 guinea pig hearts under identical conditions were obtained at control, 1, 5, 10, 20, 40, and 60 min of acute global ischemia. LV contractility diminished within 1 sec (P less than 0.01) of ischemia and dropped to less than 35% of control by 1 min. Reduction of mitochondria was detected by epicardial NADH fluorophotography at 2 sec of ischemia. Cellular pH diminished 0.3 pH units by 5 min. Adenosine triphosphate (ATP) concentration remained at control levels while phosphocreatine (PCr) dropped to 63 +/- 8.5% of control by 1 min of ischemia. CONCLUSIONS After the onset of global ischemia (1) mitochondrial electron transport ceases by 2 sec; (2) acidosis develops immediately; (3) LV contractility diminishes by 1 sec; (4) ATP concentration appears to be buffered by PCr, and is dissociated from myocardial function.

Oxygen diffusion in phospholipid artificial membranes studied by Fourier transform nuclear magnetic resonance.

Abstract Spin-lattice ( T i ) relaxation mesurements can provide information about the presence of oxygen in the environment of a nucleus, since oxygen, by virtue of its paramagnetic properties, increases T i relaxation rates. Spin-lattice relaxation times were measured for the choline, fatty acid methylene, and fatty acid methyl protons of sonicated dimyristoyl phosphatidyl choline vesicles in D 2 O at several oxygen pressures. The increase in relaxation rate due to oxygen was found to be greater for the fatty acid resonances than for the choline resonance. This was interpreted to indicate the presence of oxygen in the hydrocarbon core of the bilayer. In addition, the T i relaxation data permitted calculation of the oxygen diffusion coefficient in the water and lipid phases.