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C M Wang

Publications and source records attributed to C M Wang.

99 records · Page 6Linked to original sources
PubMed1972

The action of phospholipases on the inner and outer surface of the squid giant axon membrane.

1. The effects of phospholipases on resting potential, action potential and membrane ionic conductances of squid giant axons have been studied by means of internal perfusion and voltage clamp techniques. The sample of phospholipases used exhibited both phospholipase A and B activities.2. When applied externally, phospholipases had no effect on the resting and action potentials at a concentration of 100 mug/ml.3. When applied internally, the enzymes effectively suppressed the amplitude and maximum rate of rise of the action potential at a concentration of 100 mug/ml. The resting potential started decreasing appreciably only after the action potential had been suppressed to a considerable extent.4. Under voltage clamp conditions, the peak transient current was suppressed following internal perfusion of phospholipases, 150 mug/ml. The steady-state current began to decrease, and the leakage current to increase only after the transient current had been suppressed to a considerable extent.5. The time course of sodium inactivation was not significantly slowed by internal perfusion of the enzymes.6. The curve relating the peak transient conductance to the membrane potential was shifted in the direction of depolarization after internal perfusion of phospholipases. No appreciable shift of the steady-state conductance curve was observed.7. These experimental results are discussed in connexion with the possible role of membrane phospholipids in the conductance changes associated with excitation.

Action Potentials↗
PubMedDate not supplied

Orthogonal subspace projection-based approaches to classification of MR image sequences.

Orthogonal subspace projection (OSP) approach has shown success in hyperspectral image classification. Recently, the feasibility of applying OSP to multispectral image classification was also demonstrated via SPOT (Satellite Pour 1'Observation de la Terra) and Landsat (Land Satellite) images. Since an MR (magnetic resonance) image sequence is also acquired by multiple spectral channels (bands), this paper presents a new application of OSP in MR image classification. The idea is to model an MR image pixel in the sequence as a linear mixture of substances (such as white matter, gray matter, cerebral spinal fluid) of interest from which each of these substances can be classified by a specific subspace projection operator followed by a desired matched filter. The experimental results show that OSP provides a promising alternative to existing MR image classification techniques.

Brain↗
PubMedDate not supplied

Electrophysiological effects of antidepressants on mammalian hearts and crayfish giant axon.

Cardiotoxicity is known to occur in patients with or without preexisting cardiac diseases during treatments with the tricyclic antidepressants, amitriptyline and imipramine. The antiarrhythmic action of tricyclics was also demonstrated in clinical studies and in animal experiments. Bupropion, a novel antidepressant, is being studied in man and to date has been found to be effective and devoid of cardiovascular toxicity. This study was intended to show the direct effect of tricyclic antidepressants on excitable membrane and to compare their potential toxicity with bupropion in isolated tissues. In crayfish giant axon, all antidepressants exhibited local anesthetic-like action by reducing the action potential amplitude and maximal rate of upstroke (dv/dt). The tricyclics slowed spontaneous sinus discharges in rat atrium and prolonged the duration of evoked action potential in guinea pig atrium with a concomitant decrease in dv/dt. A quinidine-like action of the tricyclic agents is displayed in the termination of spontaneous depolarization and the suppression of dv/dt of evoked action potential in canine Purkinje fibers. The membrane depressant action of antidepressants resulted in the reduction of dv/dt and increased membrane refractoriness in both atrial and ventricular tissues; excitation is blocked even when resting membrane potential remained fully polarized. The present results confirmed the direct quinidine-like action on cardic tissues, which is probably related to the antiarrhythmic and/or cardiotoxic manifestation in man and animals. On on excitable tissues studied, tricyclic antidepressants are the most potent in blocking membrane excitation, while bupropion is the least toxic on the molar basis.

Animals↗