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R Weingart

Publications and source records attributed to R Weingart.

59 records · Page 4Linked to original sources
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↗
PubMed1974

The permeability to tetraethylammonium ions of the surface membrane and the intercalated disks of sheep and calf myocardium.

1. Efflux experiments and longitudinal diffusion experiments were performed to determine the permeability of the surface membrane and of the nexal membrane of sheep and calf ventricular muscle to radioactive [1-(14)C]tetraethylammonium cations ([(14)C]TEA) at 25 degrees C.2. Efflux curves were analysed as the sum of three exponential processes with time constants for TEA loss of 2.7, 13.3, and 832 min.3. The first component was attributed to the exchange of extracellular free TEA, the second to extracellular, probably mucopolysaccharide bound TEA, and the third to intracellular free TEA.4. From the decay of the first phase the tortuosity factor for extracellular radial movement of TEA ions was calculated as 1.59.5. The permeability of the surface membrane to [(14)C]TEA was estimated as 6.06 x 10(-8) cm/sec.6. A tenfold change of [K](o) from 5.4 to 54 mM resulted in a 2.75-fold decrease of the permeability of the surface membrane; a fifteenfold change (5.4 to 81 mM) resulted in a 4.24-fold decrease.7. From longitudinal non-steady state diffusion experiments the permeability of the nexal membrane to [(14)C]TEA turned out to be 1.27 x 10(-3) cm/sec.8. The permeability of the nexal membrane to TEA is 21,000 times larger than that of the surface membrane. This finding is consistent with the concept of low resistance pathways between myocardial cells.9. From a comparison of the dimensions of radiopotassium, [(14)C]TEA and Procion Yellow, and the study of their diffusional properties, the pores within the nexal membrane of the intercalated disks are deduced to have a diameter of somewhat more than 10 A.

Animals↗