Apamin depresses selectively the after-hyperpolarization of cat spinal motoneurons

Extra- (but not intra-) -cellularly applied apamin depresses selectively the after-hyperpolarization (AHP) of cat spinal motoneurons in situ, while causing only a slight depolarization and minor changes in size and shape of the action potential. Apamin increases firing evoked by long depolarizing current pulses. These results indicate that the Ca2+-dependent K conductance underlying the AHP is sensitive to apamin, and that this conductance is likely to have a physiological role in the control of motoneuronal firing.

Mechanism of Action of Pseudomonas syringae Phytotoxin, Syringomycin : Stimulation of Red Beet Plasma Membrane ATPase Activity

Syringomycin, a peptide toxin produced by the phytopathogen Pseudomonas syringae pv syringae preferentially stimulated (2-fold) the vanadate-sensitive ATPase activity associated with the plasma membrane of red beet storage tissue. The toxin had a very slight effect on the tonoplast ATPase and had no detectable effect on the mitochondrial ATPase. Optimal stimulation was achieved with 10 to 50 micrograms of syringomycin per 25 micrograms of membrane protein. Treatment of membranes with 0.1% (weight/volume) deoxycholate eliminated the activation effect, and enzyme solubilized with Zwittergent 3-14 was not affected by syringomycin. ATPase activity was activated to the same extent at KCl concentrations ranging from 0 to 50 millimolar. Valinomycin, nigericin, carbonylcyanide p-trifluoromethoxyphenylhydrazone, and gramicidin did not increase the plasma membrane ATPase activity. However, these ionophores did not hinder the ability of syringomycin to stimulate the activity. We suggest that syringomycin does not increase ATPase activity by altering membrane ion gradients nor directly interacting with the enzyme, but possibly through regulatory effectors or covalent modification of the enzyme.

Effects of 4-aminopyridine on the action potential and the after-hyperpolarization of cat spinal motoneurons

In cats under pentobarbital anaesthesia, intramotoneuronal administrations of 4-aminopyridine significantly prolong the falling phase of the antidromic action potential but have much less effect on the orthodromic action potential. 4-aminopyridine probably blocks the fast K channels involved in the repolarization of the membrane and indirectly activates ionic channels through enhancement of synaptic transmission, also suggested by the potentiation of excitatory postsynaptic potentials. In many cells, 4-aminopyridine depresses the amplitude and prolongs the time course of the after-hyperpolarization; therefore 4-aminopyridine may also partly block Ca2+-activated K+ channels.

Mechanism of action of Pseudomonas syringae phytotoxin, syringomycin. Interaction with the plasma membrane of wild-type and respiratory-deficient strains of Saccharomyces cerevisiae

The effects of the phytotoxin, syringomycin, produced by Pseudomonas syringae pv. syringae, were examined on cells of a wild-type and a respiratory-deficient (rho0) mutant of Saccharomyces cerevisiae. The growth of both strains in liquid culture was inhibited by 0.5 micrograms syringomycin per ml and higher. Uptake rates of tetraphenylphosphonium and dimethyloxazolidine ions in cell suspensions of both strains increased when 1.5 micrograms per ml syringomycin was added. These responses were kinetically and quantitatively similar in the two strains and indicated increases in electrical potential (cell interior negative) and pH differences (cell interior alkaline) across the plasma membrane. Glucose (0.1 M) enhanced the effect on the electrical potential, was required for the pH changes, and increased the cellular ATP levels. These results show that the effects of syringomycin are energy-dependent and are due to alterations of plasma membrane and not to mitochondrial function.

Why TCP timers don't work well

Repeated observation of TCP retransmission timer problems stimulated investigation into the roles and limitations of timers. Timers are indispensable tools in building up reliable distributed systems. However, as the experience with the TCP retransmission timer has shown, timers have intrinsic limitations in offering optimal performance. Any timeout based action is a guess based on incomplete information, and as such is bound to be non-optimal. We conclude that, if we aim at high performance, we should use external events as a first line of defense against failures, and depend on timers only in cases where external notification has failed.

[Prognostic analysis of four pathological features in carcinoma of the uterine cervix and its clinical significance]

The correlation between different pathological features of biopsy specimen and the five year survival rate of 442 patients with carcinoma of uterine cervix treated in our hospital during 1968 to 1980, were studied by means of gradual regression. The result showed that the five year survival rate was influenced, at different levels, by the pathological features. The peritumoral lymphocytic infiltration was the most significant factor influencing the prognosis. Then were the fibrous tissue reaction and the cell type but the mode of invasion was insignificant. The best regression equation to predict the prognosis of patients with carcinoma of uterine cervix was established by gradual choosing. By this equation, we could directly calculate the probability of the five year survival of the patient. It was proved by retrospective and prospective analysis that the equation could accurately reflect the real five year survival rate of patients with carcinoma of uterine cervix.

A New Heuristic Search Technique-Algorithm SA

In this paper, we present a new heuristic searching algorithm by introducing the statistical inference method on the basis of algorithm A (or A*). It is called algorithm SA. In a simplified search space, a uniform m-ary tree, we obtain the following result. Using algorithm SA, a goal node can be found with probability one, and its mean complexity is O(N·ln N) where N is the depth at which the goal is located.

Planning collision-free paths for robotic arm among obstacles

A theory for planning collision-free paths of a moving object among obstacles is described. Using the concepts of state space and rotation mapping, the relationship between the positions and the corresponding collision-free orientations of a moving object among obstacles is represented as some set of a state space. This set is called the rotation mapping graph (RMG) of that object. The problem of finding collision-free paths for an object translating and rotating among obstacles is thus transformed to that of considering the connectivity of the RMG. Since the connectivity of the graph can be solved by topological methods, the problem of planning collision-free paths is easily solved in theory. Using this theory, a topological method for planning collision-free paths of a rod-object translating and rotating among obstacles is presented. If a nonrigid robotic arm is viewed as a composite rod with some degrees of freedom, the planning of collision-free paths of a robotic arm can be solved in a similar way to a rod.