Biomedical subjects

R WERMAN

Publications and source records attributed to R WERMAN.

15 recordsLinked to original sources

PubMed1964

ANTIDROMIC INHIBITION ACCOMPANIED BY VENTRAL ROOT POSITIVITIES.

Ventral-root positivities exhibiting the time course of antidromic inhibition were recorded in the cat. Hyperpolarization of the motoneuron occurs concomitant to antidromic inhibitionwithout damage to the motoneuron. Under optimal conditions L7 and S1 ventral-root filaments show electrotonic potentials of positive sign with the time course of antidromic inhibition. Conditions predisposing to membrane depolarization are not responsible for this hyperpolarization. Antidromic inhibition was not found in roots caudal to S1.

Cats↗

PubMed1963

Electrical inexcitability of the frog neuromuscular synapse.

Frog muscle endplates were explored with an extracellular microelectrode. An intracellular microelectrode nearby simultaneously monitored invasion of the endplate by a spike directly evoked by a third microelectrode placed away from the endplate in the same fiber. External positivities were seen only at sites generating miniature endplate potentials. The external positivity reached a maximum prior to the internally recorded potential and was followed by a small late negativity. Small movements away from active synaptic sites resulted in positive-negative-positive potential sequences characteristic of activity and propagation. Since the external potential is a function of membrane current, the absence of negativity associated with the rising phase of the spike indicates the absence of inward current at synaptic sites. Thus, the synaptic membrane appears not to be excited by a depolarization of the magnitude of an action potential. In an Appendix it is shown that the late negativity and earlier maximum of the external potential can be accounted for by capacitative current through passive membrane.

Action Potentials↗

PubMed1961

Graded and all-or-none electrogenesis in arthropod muscle. I. The effects of alkali-earth cations on the neuromuscular system of Romalea microptera.

Graded electrically excited responsiveness of Romalea muscle fibers is converted to all-or-none activity by Ba(++), Sr(++), or Ca(++), the two former being much the more effective in this action. The change occurs with as little as 7 to 10 per cent of Na(+) substituted by Ba(++). The spikes now produced have overshoots and may be extremely prolonged, lasting many seconds. During the spike the membrane resistance is lower than in the resting fiber, but the resting resistance and time constant are considerably increased by the alkali-earth ions. The excitability is also increased, spikes arising neurogenically from spontaneous repetitive discharges in the axon as well as myogenically from spontaneous activity in the muscle fibers. Repetitive responses frequently occur on intracellular stimulation with a brief pulse. The data indicate that the alkali-earth ions exert a complex of effects on the different action components of electrically excitable membrane. They may be described in terms of the ionic theory as follows: The resting K(+) conductance is diminished. The sodium inactivation process is also diminished, and sodium activation may be increased. Together these changes can act to convert graded responsiveness to the all-or-none variety. The alkali-earth ions can also to some degree carry inward positive charge during activity, since spikes are produced when Na(+) is fully replaced with the divalent ions.

Alkalies↗

PubMed1961

Graded and all-or-none electrogenesis in arthropod muscle. II. The effects of alkali-earth and onium ions on lobster muscle fibers.

Conversion of graded responsiveness of lobster muscle fibers to all-or-none activity by alkali-earth and tetraethylammonium (TEA) ions appears to be due to a combination of effects. The membrane is hyperpolarized, its resistance is increased, and its sensitivity to external K(+) is diminished, all effects which indicate diminished K(+) conductance. While the spikes are prolonged, the conductance is higher throughout the response than it is in the resting membrane. Repetitive activity becomes prominent. These effects indicate maintained high conductance for an ion which causes depolarization. This is normally Na(+), since its presence in low concentrations potentiates the effects of Ba(++), but the alkali-earth ions and TEA can also carry inward charge. Ba(++), Sr(++), and TEA appear to be more effective than is Ca(++) in its normal role, which is probably to depress K(+) conductance and Na inactivation. Thus, conversion of graded to all-or-none responsiveness appears to occur because of the relative increase of depolarizing inward ion flux and decrease of repolarizing outward flux.

Alkalies↗

PubMed1961

The ionic mechanisms of hyperpolarizing responses in lobster muscle fibers.

Lobster muscle fibers develop hyperpolarizing responses when subjected to sufficiently strong hyperpolarizing currents. In contrast to axons of frog, toad, and squid, the muscle fibers produce their responses without the need for prior depolarization in high external K(+). Responses begin at a threshold polarization (50 to 70 mv), the potential reaching 150 to 200 mv hyperpolarization while the current remains constant. The increased polarization develops at first slowly, then becomes rapid. It usually subsides from its peak spontaneously, falling temporarily to a potential less hyperpolarized than at threshold for the response. As long as current is applied there can be oscillatory behavior with sequential rise and subsidence of the polarization, repeating a number of times. Withdrawal of current leads to rapid return of the potential to the resting level and a small, brief depolarization. Associated with the latter, but of longer duration, is an increased conductance whose magnitude and duration increase with the antecedent current. Hyperpolarizing responses of lobster muscle fibers are due to increased membrane resistance caused by hyperpolarizing K inactivation. The oscillatory characteristic of the response is due to a delayed superimposed and prolonged increase in membrane permeability, probably for Na(+) and for either K(+) or Cl(-). The hyperpolarizing responses of other tissues also appear to result from hyperpolarizing K inactivation, on which is superimposed an increased conductance for some other ion or ions.

Animals↗

PubMed1960