Die Impulsregeneration bei der Signalfortleitung in markhaitigen Nervenfasern.

As regards the regeneration of nervous impulses the controlling mechanism of the excitable membrane can be reduced essentially to the following two membrane properties: 1. There is a fixed voltage interval where the two different positive conductivities of the membrane change over continuously. In this transition region if the membrane potential is more positive the current-voltage characteristic shows a negative differential resistance. This characteristic may be measured under steady-state conditions in the presence of the particular ions (K., Rb., and during veratridine-poisoning also Na., Li., NH4 ., C(NH2)3 .) acting as charge carriers during excitation. 2. In addition Na.-K.-selectitivity is observed which effects a faster penetration of Na. than of K. through the membrane. At present the molecular basis of both properties is unknown. But each property can be changed independently of the other. Physicochemical means (e.g., variation of pH, osmolarity, solvent, concentration of bivalent cation) act unpon the shape of the current-voltage relation by shifting the transition region, while the selectivity is changed by the presence of pharmacological agents (local anaesthetics such as cocain, tetrodotoxin, veratridine). So it may be advantageous to localize and characterize the action on membrane structure common to all members of each group of agents in order to approach the molecular origin of the basic membrane properties

Shear dependence of the fibrin coagulation kinetics in vitro.

Fibrin thrombus formation, in vivo and in vitro, preferentially occurs in regions of retarded, recirculating flow which promote local variations of the distribution of blood components, e.g. thrombin, and shear rates. To better understand the effects of shear forces on the thrombin induced fibrin coagulation process the time course of fibrin formation in a fibrinogen/thrombin solution was studied for different shear rates γ̇ (0 s-1 ≤γ̇ ≤500 s-1) and thrombin concentrations c(thr) (0.1 units/ml≤c(thr)≤1.0 units/ml). The clotting curves at zero shear and the shear induced alterations of these curves could essentially be described in terms of a reaction kinetics defined by two rate coefficients k1, k2 which can be attributed to fibrinogen cleavage by thrombin and fibrin polymerisation, respectively. For c(thr)≥O0.5 units/ml and γ̇≥O15s-1 an additional mechanism, presumably fibrin breakage, had to be assumed. The rate coefficient k2 was markedly more affected by c(thr) and shear forces then was k1. The results fit well to the growth kinetics of fibrin thrombi formed in glas models of an arterial branching

 Über die Bedeutung paranodaler Strukturen für die Impulsregeneration am Ranvier´schen schnurring.

The site of the pulse regeneration in myelinated nerve is generally assumed to be the unmyelinated part of the axon membrane in the Ranvier node. To check this, a microirradiation technique using laser pulses (λ=347 nm, t=20 ns) was used to produce morphological lesions of about 1 μm diameter in various regions of the Ranvier node. The electrophysiological functions were monitored parallel to the irradiation. Depending on the localization of the lesions two types of changes in these functions were observed: If a definite site in the paranodal myelin sheath was damaged without affecting the axon, an action potential could no longer be elicited, although the resting potential as well as the stationary current voltage behavior remained unchanged. A damage of the axon resulted in a breakdown of membrane potential and resistance. In most of the cases the excitability recovered after spontaneous or current induced restitution of the membrane resting potential and resistance. These observations indicate that structures in the paranodal region are vital for the Na activation and inactivation. The membrane potential and stationary current voltage behavior can be attributed to the axon membrane. A new hypothesis concerning the mechanism of the Na+ activation/inactivation process is suggested