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S Weidmann

Publications and source records attributed to S Weidmann.

9 recordsLinked to original sources
PubMed1987

Cardiac cellular electrophysiology: past and present.

The time-course of the cardiac action potential can be accounted for in terms of ionic currents crossing the cell membranes. Depolarizing current is carried by Na+ or Ca2+ entering the cells, repolarizing current by K+ leaving the cells. Membrane permeability for the passive movement of these ions is thought to be voltage-dependent as well as time-dependent. Net transfer of charge may also result from active transport, 2 Na+ out against 1 K+ in; or coupled exchange, 3 or 4 Na+ in against 1 Ca2+ out. This review follows the path by which present-day knowledge has been reached. It also gives a few examples to illustrate that electrophysiology has provided concepts useful to clinical cardiology.

Action Potentials↗
PubMed1977

Effects of palytoxin on the electrical activity of dog and rabbit heart.

Reversible effects of palytoxin, extracted from colonies of the soft coral Palythoa caribaeorum, are described. There is a decrease of both membrane resting potential and overshoot during activity. Rise time of the action potential is prolonged, while repolarization is shortened. The electrical events resemble those seen with metabolic poisons.

Acrylamides↗
PubMed1975

Low resistance pathways between myocardial cells.

To test the hypothesis of whether the intercalated discs represent a low resistance to diffusing ions, a method was developed to study the longitudinal diffusion of radioactive potassium (42K), tetraethylammonium ([14C]TEA), and the fluorescent dye Procion yellow (PY) in sheep and calf heart bundles. The method involved 1) loading the cells, 2) allowing the ions to diffuse for periods of 2-6 hr, 3) freezing the bundle in liquid air and cutting it into equal slices of 0.5 mm, 4) measuring the concentration of the ion in each slice. From the results, the diffusion of coefficients were considered to be due partially to the discs and partially to the myoplasm. The permeabilities of the nexal membranes were 7.68-10(-3), 1.27-10(-3), and 1.4-10(-6) cm/sec for 42K, 14C-TEA, and PY. These values are 9,600, 21,000, and 220 times more than the corresponding ones for the surface membrane. The disc resistance for potassium, the main intracellular charge carrier, was about 0.9 ohm cm2. From the van der Waals sizes of the ions, the diameter of the nexal pores has to be 10-15 A. It is concluded that the junctions between myocardial cells have low resistances and that propagation of action potentials is possible by local circuit currents.

Animals↗
PubMed1975

[Propagation of stimuli].

Cardiac muscle is considered as a biological cable, similar to fibres of skeletal muscle or nerve. "Local currents" within the core of the cable and through the extracellular space are responsible for the propagation of membrane excitation. Conduction velocity depends on (i) fibre diameter, (ii) specific resistance of the core and interstitial fluid, (iii) strength of possible inward current through the surface membrane. Conduction delay and possible block is found at sites of transition between terminal Purkinje fibres and ventricular muscle. Monophasic action potentials of somewhat different shapes are recorded from various parts of the heart. A slow upstroke is characteristic for sites of low conduction velocity (SA-node, AV-node). A progressive decrease of resting potential in the phase of diastole is typical for regions showing a tendency to automatic impulse generation (SA-node, AV-node, Purkinje fibres). Cardiac muscle is a functional syncytium. This statement is based on (i) measurements of electrical resistance between cells and (ii) diffusion experiments using tracer substances. Progressive de-coupling is observed under various pathological conditions, resulting in slow conduction or block.

Action Potentials↗
PubMed1973

[Ectopic beats].

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Action Potentials↗