Comparison of the morphology, antigenicity, and pathology of Nichols and Birmingham isolates of Treponema pallidum.

A strain of Treponema pallidum isolated from a homosexually acquired penile chancre in Birmingham in 1979 was serially passaged in rabbits and compared with the Nichols strain. The two strains appeared identical morphologically, and no gross differences were detected on antigenic analysis by two-dimensional immunoelectrophoresis. The Birmingham strain was, however, considerably less virulent for rabbits; the number of organisms required for equivalent time of development and severity of skin lesions was 10-fold to 100-fold greater for the Birmingham than for the Nichols strain.

Delayed kinetics of squid axon potassium channels do not always superpose after time translation.

The activation of potassium ion conductance in squid axons by voltage-clamp depolarization is delayed when the depolarizing step is preceded by a conditioning hyperpolarization of the axonal membrane. Moreover, the control conductance kinetics superpose with the delayed kinetics when they are translated along the time axis by an amount equal to the delay. We have found that the degree of superposition with internally perfused axons depends upon voltage-clamp protocol.

Developmental changes in subthreshold pace-maker currents in chick embryonic heart cells.

1. Small re-aggregates of cells dissociated from the ventricles of 12-or 17-day-old chick embryonic hearts have beating properties in low potassium tissue culture medium which differ from re-aggregates prepared from 7-day-old hearts; 12-day preparations either beat with a slower rate than comparable-size 7-day preparations or they are quiescent; 17-day preparations usually do not beat. 2.

Analysis of subthreshold pace-maker currents in chick embryonic heart cells.

1. Small re-aggregates of cells dissociated from the ventricles of 7-day-old chick embryonic hearts beat spontaneously in low external potassium concentration (Ko = 1.3 mM) tissue culture medium.

Pacemaker currents in chick embryonic heart cells change with development.

The initial heartbeat of the chick embryo occurs shortly after the first day of incubation. The pacemaker of this beat originates in the region of the primitive heart destined to become sinoatrial tissue in the adult. Individual cells isolated from the atrial and ventricular portions of the embryonic heart are also capable of beating spontaneously at this stage.

Fluctuations in interbeat interval in rhythmic heart-cell clusters. Role of membrane voltage noise.

Small clusters of ventricular cells prepared from 7-d chick heart maintain spontaneous, stationary, rhythmic beating in culture for many hours. For clusters containing I-125 cells, mean interbeat interval (IBI) is 0.45 +/- 0.

Current noise parameters derived from voltage noise and impedance in embryonic heart cell aggregates.

We have recorded membrane impedance and voltage noise in the pacemaker range of potentials (-70 to -59 mV) from spheroidal aggregates of 7-d embryonic chick ventricle cells made quiescent by exposure to tetrodotoxin in medium containing 4.5 mM K+. The input capacitance is proportional to aggregate volume and therefore to total membrane area.

Comparison of ion current noise predicted from different models of the sodium channel gating mechanism in nerve membrane.

The theoretical power density spectrum S(f) of ion current noise is calculated from several models of the sodium channel gating mechanism in nerve membrane. Sodium ion noise experimental data from the frog node of Ranvier [Conti, F., et al.

Random walk analysis of potassium fluxes associated with nerve impulses.

We present a novel recursion method for obtaining theoretical expressions for unidirectional single-file fluxes of ions through narrow membrane channels containing an arbitrary number of ion sites. The theory is applied to experimental tracer fluxes associated with nerve impulses from cephalopod giant axon membranes at various temperatures between 7 degrees and 27 degrees. The comparison between the theoretical and experimental one-way fluxes suggests that the potassium channel in nerve membrane contains three ion sites, which is consistent with the deduction by Hodgkin and Keynes that the potassium channel contains two or three sites on the basis of the ratio of tracer influx to tracer efflux.

Theoretical model of the ionic mechanism of 1/f noise in nerve membrane.

A model is presented for the ionic mechanism of low frequency 1/f electrical noise which has been observed in axonal membranes. The model consists of narrow channels which open randomly throughout the membrane and remain open for only a short time compared with f-1max where fmax approximately 2 kHz is the maximum frequency for which 1/f noise is observed. The fluctuation in channel formation is coupled to low frequency normal mode vibrations in liquid crystals which have properties similar to nerve membranes.