Leak Current Rectification in Myxicola Giant Axons : Constant field and constant conductance components

Early leak current, i.e. for times similar to the time to peak of the transient current was measured in Myxicola giant axons in the presence of tetrodotoxin. The leak current-voltage relation rectifies, showing more current for strong depolarizing pulses than expected from symmetry around the holding potential. A satisfactory practical approximation for most leak corrections is constant resting conductance. The leak current-voltage curve rectifies less than expected from the constant field equation. These curves cannot be reconstructed by summing the constant field currents for sodium and potassium using a P_Na/P_K ratio obtained in the usual way, from zero current constant field fits to resting membrane potential data. Nor can they be reconstructed by summing the constant field current for potassium with that for any other single ion. They can be reconstructed, however, by summing the constant field current for potassium with a constant conductance component. It is concluded that the leak current and the resting membrane potential, therefore, are determined by multiple ionic components, at least three and possibly many. Arguments are presented suggesting that ion permeability ratios obtained in the usual way, by fitting the constant field equation to resting membrane potential data should be viewed with skepticism.     

Computation of Impulse Conduction in Myelinated Fibers; Theoretical Basis of the Velocity-Diameter Relation

For myelinated fibers, it is experimentally well established that spike conduction velocity is proportional to fiber diameter. However no really satisfactory theoretical treatment has been proposed. To treat this problem a theoretical axon was described consisting of lengths of passive leaky cable (internode) regularly interrupted by short isopotential patches of excitable membrane (node). The nodal membrane was assumed to obey the Frankenhaeuser-Huxley equations. The explicit diameter dependencies of the various parameters were incorporated into the equations. The fiber diameter to axon diameter ratio was taken to be constant, and the internode length was taken to be proportional to the fiber diameter. Both these conditions reflect the situation that exists in real, experimental fibers. Dimensional analysis shows that these anatomical conditions are equivalent to Rushton's (1951) assumption of corresponding states. Hence, conduction velocity will be proportional to fiber diameter, in complete agreement with the experimental findings. Digital computer solutions of these equations were made in order to compute a set of actual velocities. Computations made with constant internode length or constant myelin thickness (i.e., nonconstant fiber diameter to axon diameter ratio) did not show linearity of the velocity-diameter relation.     

SPORADIC ACUTE GLOMERULONEPHRITIS IN ADULTS

Nineteen adults who had acute glomerulonephritis were reviewed with respect to the clinical course and long-term follow-up. The age range was from 17 to 55 years. Only one patient died during the acute episode. In 11 cases, onset occurred between November and January and 15 of the patients had a known respiratory tract infection three to 30 days before the onset. The most important symptoms noted were weight gain, edema, dyspnea, oliguria and red or smoky urine. The most prominent physical signs were elevated blood pressure, edema, abnormalities in the chest and fever of over 100° F. Fifteen patients showed roentgen evidence of pulmonary vascular congestion, pleural effusion, cardiomegaly, pneumonia or a combination of these abnormalities. All the patients had proteinuria and red blood cells in the urine, and half of them had red blood cell casts. Azotemia, when present, subsided in 9.4 days. The average diastolic pressure was 105 mm. of mercury and the mean fall was 26 mm. in 23.5 days. At six months, nine of the 13 patients still being observed continued to show proteinuria or microscopic hematuria (seven showed both). A late follow-up of ten patients showed one to have significant hypertension and one to have early functional impairment and inconstant proteinuria. In these cases the average blood pressure was 140/91 mm. as compared with 119/74 mm. at the time of discharge.Sporadic glomerulonephritis in adults presents essentially the same pattern as it does in children. Urinary abnormalities may persist for months or even years, and neither the present series nor those reported by others clearly reveal the ultimate prognosis.     

A Molecular Structural Basis for the Excitation Properties of Axons

A structural model is suggested for axon membranes consisting of a double layer of lipid and phospholipid molecules in which the polar ends of certain phospholipids change their orientation and combining properties under the influence of an electric field. The phosphate groups act as ion exchange “gates” for the control of ion flow through the membrane. Expressions are developed for the calculation of membrane current components as functions of time, potential, and ionic environment. Approximate solutions show fairly good agreement with existing experimental data in a number of different respects such as steady-state current-voltage relations, the effect of calcium on steady-state current, potassium tracer flux ratios, initial current and rate of change of current, and the dependence of the time constants of current change on membrane potential.