Cellular Volume Changes Research Articles

Cell Volume as a Factor Influencing Electrical and Mechanical Activity of Vascular Smooth Muscle

The effects of variations in the extracellular osmolarity on the electrical and mechanical activity of the isolated rat portal vein were studied. Addition of sucrose or xylose (20–100 mmoles/l) to the “normal” solution caused inhibition of contractile activity which could be ascribed to changes in the electrical discharge pattern. Increasing osmolarity with urea produced transient inhibition, return to control activity, and, on return to normal solution, a transient excitation. Reducing osmolarity by 30–60 mOsm/l by decreasing the [Na+] and [Cl] of the medium caused sustained excitation with continuous spike discharge and tetanic contraction. Comparable decreases in the ionic concentrations but with osmotic substitution by sucrose or xylose had little influence on muscle activity. Substituting Na+ and Cl with urea on an equiosmolar basis caused excitation resembling that in hypoosmotic solution. If the smooth muscle cells are looked upon as osmotic cells with membranes that are freely permeable to H2O and urea but less permeable to sugar and ions, the results indicate a consistent correlation between cell volume and state of activity; shrinkage associated with inhibition, swelling with excitation. Changes in the transuiembrane concentration gradients for K+, Na+ and Cl-, caused by the cellular volume changes, are not sufficient to explain the electrical responses. Changes in ionic membrane permeability are assumed to occur.

Lipid cytochemistry and morphologic change in aging populations of Tetrahymena.

SYNOPSIS. In cultures of strains GL, S, W, and WH6 of Tetrahymena pyriformis grown in proteose‐peptone medium and stained with phosphine 3R the percentage of cells containing lipid granules increased in early stationary phase, decreased in the middle of stationary phase, and increased again toward the end of culture life. Granules appeared first in the anterior ends of cells and spread thruout the cytoplasm as the cultures aged. These granules consisted of neutral fat and were present in living cells. Changes in lipid accumulation were correlated with changes in cellular size, shape, volume and fragility.

CAT HEART MUSCLE IN VITRO. 8. ACTIVE TRANSPORT OF SODIUM IN PAPILLARY MUSCLES.

The cells of cat right ventricular papillary muscles were depleted of K and caused to accumulate Na and water by preincubation at 2-3 degrees C. The time courses of changes in cellular ion content and volume and of the resting membrane potential (V(m)) were then followed after abrupt rewarming to 27-28 degrees C. At physiological external K concentration ([K](o) = 5.32 mM) recovery of cellular ion and water contents was complete within 30 minutes, the maximal observable rates of K uptake and Na extrusion (Deltammol cell ion/(kg dry weight) (min.)) being 3.4 and 3.6, respectively. The recovery rate was markedly slowed at [K](o) = 1.0 mM. Rewarming caused V(m) measured in cells at the muscle surface to recover within from <1 to 9 minutes, but only slight restoration of cellular ion contents (measured in whole muscles) had occurred after 10 minutes. Studies of recovery in NaCl-free sucrose Ringer's solution made it possible to separate the ouabain-insensitive outward diffusion of Na as a salt from a simultaneous ouabain-sensitive Na extrusion which is associated with a net cellular K uptake. A hypothesis consistent with these observations is that rewarming may activate a ouabain-sensitive "electrogenic" mechanism, most probably the net active transport of Na out of the cell, from which net K uptake may then follow passively.

SOME CHARACTERISTICS OF THE PROXIMAL TUBULAR WALL RELATED TO REABSORPTION DURING LUMINAL OCCLUSION FOLLOWING INTERRUPTION OF GLOMERULAR FILTRATION.

AbstractThe purpose of this investigation was to study the hydrostatic pressure changes within and outside the proximal tubules and to study possible changes in proximal cellular volume during the occlusion period following abruption of the renal blood flow and filtration. The pressures were measured directly using the micropuncture technique. The results demonstrate that the proximal tubular wall can resist a modest positive hydrostatic pressure from either the inside or the outside of the cellular wall for a short time interval. During reabsorption in the occlusion period a positive pressure seems to be created in the lumen of the proximal tubules probably due to “interfacial tension” and a positive luminal pressure is maintained until all the fluid has disappeared.The proximal cellular volume was estimated from the cellular area of cross‐sectioned proximal tubules of snap‐frozen kidneys. The area was measured by planimetry. It was demonstrated that the cellular area is the same (within about 10%) at the various rates of transcellular transport of sodium associated with spontaneous variations of the rate of glomerular filtration, and that it remains unchanged during the whole occlusion period. An increase of about 50% in the cellular volume occurred as soon as the luminal fluid was reabsorbed, i. e. about 20 sec after interruption of the renal circulation. The cellular volume then remained unchanged for several minutes.