APPARENT VIOLATIONS OF THE ALL-OR-NONE LAW IN RELATION TO POTASSIUM IN THE PROTOPLASM

In Vol. 37, No. 6, July 20, 1954, page 814, in the third paragraph, delete the first sentence and insert the following: This equation gives excellent results with Nitella for example with 0.001 M KCl outside and 0.05 M KCl in the sap we may use concentrations in place of activities in the equation and put a_s = 0.05 and a_o = 0.001. No allowance is made for any change in the concentration of incoming ions due to their combination with carrier molecules since this change would be small and difficult to estimate. If we put U = 73 and V = 1 we obtain P = 97 mv. which is close to the usual observed value. The expression (73 –1) ÷ (73 + 1) = 0.973.     

Tempo and mode of concerted evolution in the L1 repeat family of mice

A 300-bp DNA sequence has been determined for 30 (10 from each of three species of mice) random isolates of a subset of the long interspersed repeat family L1. From these data we conclude that members of the L1 family are evolving in concert at the DNA sequence level in Mus domesticus, Mus caroli, and Mus platythrix. The mechanism responsible for this phenomenon may be either duplicative transposition, gene conversion, or a combination of the two. The amount of intraspecies divergence averages 4.4%, although between species base substitutions accumulate at the rate of approximately 0.85%/Myr to a maximum divergence of 9.1% between M. platythrix and both M. domesticus and M. caroli. Parsimony analysis reveals that the M. platythrix L1 family has evolved into a distinct clade in the 10-12 Myr since M. platythrix last shared a common ancestor with M. domesticus and M. caroli. The parsimony tree also provides a means to derive the average half-life of L1 sequences in the genome. The rates of gain and loss of individual copies of L1 were estimated to be approximately equal, such that approximately one-half of them turn over every 3.3 Myr.      

TGF-beta expression during rat pregnancy and activity on decidual cell survival

Background  

During early rat pregnancy, trophoblast of the tiny embryo joins with the endometrium and epithelial cells undergo apoptosis. Near the end of pregnancy, regression of the decidua basalis (DB) is also observed (from day 14 to 20). However, little is known about the intra-cellular and molecular mechanisms involved in apoptosis regulation in the uterus during pregnancy. The objective of the present study was to investigate the presence and the developmental expression of transforming growth factor-beta isoforms (TGF-beta well known differentiation factor) in the rat endometrium throughout pregnancy and its action in vitro using cultured endometrial stromal cells.     

NATURE OF THE ACTION CURRENT IN NITELLA : IV. PRODUCTION OF QUICK ACTION CURRENTS BY EXPOSURE TO NACl

Treatment of Nitella with NaCl greatly reduces the time required for the action current and produces an action curve with one peak instead of the customary two. The time may be reduced to 0.6 second in place of the usual 15 to 30 seconds. This might be expected if the treatment increased the conductivity of the aqueous part of the protoplasm. The experiments favor this idea although they do not prove its correctness. This effect is prevented by calcium, possibly because calcium inhibits penetration of salts. That penetration is an important factor is indicated by the fact that salts which might be expected to penetrate rapidly have the most effect. Thus NaSCN is more effective than NaCl but Na₂SO₄ has little or no effect. The action of NH₄Cl and LiCl is similar to that of NaCl.     

THE PENETRATION OF STRONG ELECTROLYTES

The entrance of strong electrolytes into Valonia is very slow unless the cells are injured. This, together with the very high electrical resistance of the protoplasm, suggests that they may penetrate largely as undissociated molecules formed at the surface of the protoplasm by the collision of ions. Under favorable circumstances KCl may be absorbed to the extent of 3 x 10^–8 mols per hour per sq. cm. of surface together with about 0.17 as much NaCl. Other substances which seem to penetrate to some extent are Li, Rb, Br, BrO₃, I, IO₃, and selenite. Little or no penetration is shown by SCN, ferricyanide, ferrocyanide, formate, salicylate, tungstate, seleniate, NO₂, SO₃, Sb, glycerophosphate, and many heavy metals and the alkaline earths. In sea water whose specific gravity had been increased by CsCl cells of Valonia floated for over a year and there was little or no penetration of Cs except as the result of injury. The penetration of NH₄Cl decreases the specific gravity of the sap and causes the cells to float: under these circumstances they live indefinitely. It is probable that NH₃ or NH₄OH penetrates and is subsequently changed to NH₄Cl. It would seem that if the sea contained a little more ammonia this would be a floating organism.     

ANESTHESIA IN ACID AND ALKALINE SOLUTIONS

The action of distilled water in producing anesthesia (loss of response to electrical stimulation) in Nitella is hastened by the addition of acid and alkali and retarded by the addition of calcium. The loss of irritability is fully reversible.     

THE KINETICS OF PENETRATION : V. THE KINETICS OF A MODEL AS RELATED TO THE STEADY STATE

An organic potassium salt, KG, passes from an aqueous phase, A, through a non-aqueous layer, B, into a watery solution, C. In C it reacts with CO₂ to form KHCO₃. The ionic activity product (K) (G) in C is thus kept at such a low level that KG continues to diffuse into C after the concentration of potassium becomes greater in C than in A. Hence potassium accumulates in C, the osmotic pressure rises, and water goes in. A steady state is eventually reached in which potassium and water enter C in a constant ratio. The rate of entrance of potassium (with no water penetrating into C) may fall off in a manner approximately exponential. But water enters and may produce an exponential decrease in concentration. This suggests that the kinetics may be treated like that of two consecutive monomolecular reactions. Calculations made on this basis agree very well with the observed values. The rate of penetration appears to be proportional to the concentration gradient of KG in the non-aqueous layer and in consequence depends upon the partition coefficients which determine this gradient. Exchange of ions (passing as such through the non-aqueous layer) does not seem to play an important rôle in the entrance of potassium. The kinetics of the model may be similar to that of living cells.     

ON THE IMPORTANCE OF MAINTAINING CERTAIN DIFFERENCES BETWEEN CELL SAP AND EXTERNAL MEDIUM

A striking difference exists between the internal and external solution in the case of Valonia macrophysa. If this difference is abolished by placing cells in their own sap most of them quickly die. There is some ground for believing that the maintenance of differences between the sap and the external medium is of importance for vital processes. The sap of Valonia macrophysa is not a balanced solution in the ordinary sense and the question may be raised whether in general the interior of the cell requires a balanced solution in order to maintain life: or it may be that we must distinguish between internal and external balanced solutions.