[Age-related heart function in patients with healthy hearts]. / Altersabhängigkeit der Herzfunktion bei Herzgesunden.

Left ventricular function was investigated at rest and during submaximal exercise in 191 healthy subjects, including 46 women, by means of radionuclide ventriculography (RNV). As global parameters of heart function, ejection fraction (EF) and maximal rates of volume change during systole (VS) and diastole (VD) as well as endsystolic volume (ESV) were determined. These parameters were calculated for four age groups with mean ages of 32, 45, 55, and 64 years, respectively. At rest, heart rate (HR), EF, VS, and ESV were not significantly different in all age groups, whereas VD decreased with increasing age from 3.3 +/- 0.6 s-1 to 2.6 +/- 0.6 s-1. During exercise, HR, EF, VS, and VD increased in all groups, but less in the elderly. The smaller increase of EF and VD could be accounted for by HR alone. VS was both HR- and age-dependent. The age dependence of VD (at rest) and VS (under exercise) may reflect a reduction of myocardial compliance with increasing age. Differences of EF and VS with respect to sex were not observed, whereas VD was slightly lower in males.

[MR tomography in cardiology. II: Flow phenomena]. / MR-Tomographie in der Kardiologie. II: Flussphänomene.

Flow phenomena modify the information of MR tomograms and can cause artefacts which degrade the image quality. When ECG triggering and suitable modes of excitation are used, flow effects can give diagnostically relevant information concerning global and regional cardiac function and blood flow in vessels. The signal intensity of blood excited by an SE-mode is usually low. The spin echo increases due to the TR-effect. However, the TE-effect reduces the signal of flowing blood with increasing flow velocity. Phase shifts caused by flow generate line-shaped artefacts in the reconstructed tomograms and decrease the signal intensity of all odd spin echoes. The second order phase errors are compensated by phase recombination occurring in all even echoes. Therefore, in double echo acquisition the second spin echo of flowing blood can be higher than the first echo, especially when the flow velocity is physiologically or pathologically reduced. In multi-slice acquisition, time-of-flight effects can be observed, by which a resonance signal induced in one particular slice is shifted to and recorded in another slice.

[NMR tomography in cardiology. I. Anatomy of the healthy heart]. / NMR-Tomographie in der Kardiologie. I. Anatomie des gesunden Herzens.

The normal anatomy of the heart and the neighboring large vessels of a healthy volunteer is depicted in ECG-triggered NMR tomograms. The tomograms were recorded with a slice thickness of 10 mm without gap in transversal, sagittal and coronal orientation. They show a variety of anatomical and morphological details which cannot be obtained by means of other noninvasive imaging modalities.

Postsynaptic actions of ethanol and methanol in crayfish neuromuscular junctions.

Actions of ethanol and methanol on excitatory postsynaptic channels activated by quisqualate were investigated in opener muscles from the first walking leg and the claw of crayfish. Both ethanol and methanol reduced the elementary currents [i] that flow through channels operated by quisqualate in a concentration-dependent manner but did not affect the apparent mean open time, tau noise, of the channels estimated from power spectra. 0.26 mol/l ethanol, or 1 mol/l methanol, respectively, reduced [i] e-fold. Ethanol also markedly decreased the size and the decay time constant tau (sEPSCs) of spontaneous excitatory postsynaptic currents (sEPSCs). At ten fibres, on the average, 0.26 mol/l ethanol decreased tau (sEPSCs) by a factor 1.56 +/- 0.24 (SD). tau (sIPSCs) and tau noise of inhibitory postsynaptic currents apparently were not affected by ethanol. Moreover the size of elementary inhibitory postsynaptic currents did not decrease in the presence of this alcohol. Thus, in crayfish opener muscles ethanol seems to selectively depress excitatory postsynaptic currents.

Excitatory postsynaptic channels operated by quisqualate in crayfish muscle.

Small crayfish muscle fibers were voltage clamped and membrane current noise elicited by bath application of quisqualate, a compound structurally related to the excitatory transmitter glutamate, was measured. It was found that quisqualate activates the same excitatory postsynaptic receptors as glutamate but its affinity for these receptors is about one hundred times larger. Noise analysis revealed that the high potency of quisqualate was attributable in part to an increased apparent mean channel open time, tau noise (quisqualate), which was about ten times larger than on activation by glutamate. The channel conductance gamma(quisqualate), however, was about three times smaller than gamma(glutamate). At T = 8 C and E = -60 mV, tau noise (quisqualate) = 9.3 +/- 1.8 ms and gamma(quisqualate) = 9.7 +/- 1.1 pS resulted. tau noise (quisqualate) decreased with hyperpolarization but it was much less voltage dependent than tau noise (glutamate): tau noise (quisqualate) = 6.0 ms . exp (E/362 mV). Both gamma(quisqualate) and alpha = tau noise (quisqualate) increased with temperature (Q10 approximately 1.6). This temperature dependence was characterized by the temperature independent activation energies E gamma = 29.1 +/- 1.7 kJ/mol and E alpha = 33.9 +/- 1.3 kJ/mol. Concanavalin A which blocks desensitization of the quisqualate/glutamate receptors did not influence tau noise (quisqualate) significantly.

Glutamate activated postsynaptic channels in crayfish muscle investigated by noise analysis.

Excitatory synaptic channels in crayfish muscle were investigated under various experimental conditions. Small muscle fibres of length l less than or equal to 0.6 mm were voltage clamped, spatial control of the voltage being sufficient up to at least 500 Hz. Excitatory synaptic current was induced by superfusion of glutamate. The power density spectra of this current could be fitted by single component Lorentz curves. The analysis revealed a mean open time tau noise = 0.93 ms and a conductance gamma = 32.3 pS of the glutamate operated ion channels (membrane potential E = -60 mV, temperature T = 8 degrees C). Both the conductance gamma and the channel closing rate alpha = tau -1 noise increased significantly with temperature (Q10 approximately 2). The temperature dependence of gamma and alpha could be described by Arrhenius equations with the temperature independent activation energies E gamma = 42.3 kJ/mol and E alpha = 50.2 kJ/mol. alpha also dependent on the membrane potential, increasing about e-fold when the membrane was hyperpolarized by 120 mV. The potential dependence varied considerably from fibre to fibre. The mean channel open time tau noise agreed with the time constant of decay tau (sEPSC) of spontaneous excitatory postsynaptic currents (sEPSCs).

Effects of concanavalin A on glutamate operated postsynaptic channels in crayfish muscle.

Small crayfish muscle fibres were voltage clamped, and synaptic current noise induced by bath application of glutamate was measured. Desensitization of the glutamate receptors was blocked by preincubating the fibres with 0.3-1.0 mumol/l concanavalin A (Con A) for at least 30 min. The power density spectra of the glutamate current noise could be fitted by single component Lorentz curves. The lectin Con A did not influence significantly the conductance gamma of the glutamate channels but increased their mean open time, tau noise. The respective mean values found at T = 8 degrees C and E = -60 mV were gamma = 23.5 +/- 7.0 pS and tau noise = 1.5 +/- 0.2 ms. Both the conductance gamma and the closing rate alpha = tau -1 noise increased with temperature (Q10 approximately 1.9). This temperature dependence was characterized by the activation energies E gamma = 35.2 +/- 7.1 kJ/mol and E alpha = 46.9 +/- 2.1 kJ/mol. The potential dependence of tau noise was almost completely abolished by Con A.

Analysis of miniature spontaneous inhibitory postsynaptic currents (sIPSCs) from current noise in crayfish opener muscle.

Deviating from the normal situation, some crayfish muscle fibres showed spontaneous inhibitory activity: discharge of large inhibitory postsynaptic currents, IPSCs, alternating with long lasting bursts of current noise. Analysis of the bursts of current noise revealed that they are composed of spontaneous miniature unit currents, sIPSCs. In the burst periods the sIPSCs occurred with an average rate of 3.5--10 k Hz and had an amplitude of about alpha = 90 pA at a driving force delta E = 10 mV. The peak conductance gamma alpha = alpha/delta E of the sIPSCs was gamma alpha = 9.2 nS +/- 0.5 (S.D., n = 5) for membrane potentials between E = --60 mV and E = --80 mV. gamma alpha seemed to decrease when the membrane was hyperpolarized. The time constants of decay, tau of the sIPSCs were identical with tau of the IPSCs. Further, tau and its potential dependence agreed with the mean lifetimes of inhibitory postsynaptic channels operated by gamma-aminobutyric acid (GABA) [Dudel et al. 1977, 1980]. Synchronized opening of about 750 inhibitory synaptic channels generates a sIPSC. Analysis of this anomalous bursting inhibitory activity thus yields the size of the inhibitory quantum of transmission, which could not be obtained from IPSCs.

Efficacy of the two-microelectrode voltage clamp technique in crayfish muscle.

Crayfish muscle fibres of different dimensions were voltage clamped and white noise current was injected into the fibres at various distances from the voltage clamp current electrode. The clamp current was measured and power spectral densities were calculated. This method revealed the efficacy of the voltage clamp in these fibres. In large fibres (l = 1.8-2.0 mm; diameter = 100-180 micrometer) a space clamp was achieved only for a band width delta f = 40 Hz. At a distance of 100 micrometer from the clamp electrodes delta f was 250-500 Hz. In fibres of medium size (l = 1.0-1.3 mm; diameter = 60-120 micrometer) delta f was about 80 Hz and about 800 Hz at a distance of 100 micrometer. In experiments with very small muscle fibres (l = 400-600 micrometer; diameter = 30-50 micrometer) delta f was more than 500 Hz. The improvement of the space clamp for the smaller muscle fibres resulted mainly from the reduced total membrane capacity, cm, of these fibres. The limitations of the space clamp could be derived from the impedance properties of the fibres. The band width of the space clamp correlated with the band width for which the square of the absolute impedance, /Zp/2, of the muscle fibre could be described by a simple RC-model. This correlation was demonstrated in a model circuit. Power density spectra of membrane current fluctuations were measured also. To optimize the resolution of these measurements the contribution of instrumental noise was minimized. The effects of instrumental noise are discussed.

Inhibitory synaptic channels activated by gamma-aminobutyric acid (GABA) in crayfish muscle.

Small crayfish muscle fibres were voltage clamped and synaptic current elicited by superfused GABA solutions was measured. Analysis of the fluctuations of synaptic current and of relaxations of the current after voltage steps yielded analogous results. The current has two components. The first component is characterized by the opening of synaptic channels with a single channel conductance gamma = 9 pS and an average open time tau = 5 ms, measured at 23 degrees C and - 100 mV. tau depends on the membrane potential, tau E = tau 0 x eE/epsilon, and epsilon was about +100 mV in the average. The channel open time agrees with the time constant of decay of the inhibitory postsynaptic current (IPSC) elicited by a nerve stimulus. The current is carried by chloride ions. The second current component is much slower, the average channel open time was tau s = 33 ms at 23 degrees C and -60 mV. The open time tau s of the slow component also was shortened on hyperpolarization. The reversal potential for the current component was more positive than -50 mV. This slow component also seems to be a synaptic one.