[Influence of "zero" magnetic field on the growth of embryonic cells and primary embryos of mouse in vitro].

The present investigation reveals that a 250-fold screening of the geomagnetic field ("zero" geomagnetic fields, 200 nT) is a biologically active factor that adversely affects embryonic cells and the processes of early embryogenesis as a whole. In particular, the cultivation of primary embryonic fibroblasts in "zero" geomagnetic fields causes reduces the capacity for adhesion and proliferation, changes the monolayer morphology and increases cell death. In a more highly organized experimental model, two-celled mouse embryos, the exposure to the "zero" field results in an increase of plasma membrane permeability for dyes, a reorganization of the cytoskeleton because of alpha-actin redistribution, and the disturbance of the spatial orientation of blastomeres. As a result, the development of two-celled mouse embryos stops, and they do not reach the stage of blastocyst. These data show the significant role of geomagnetic fields in the normal growth of embryonic cells in vitro and the regulation of mammalian embryogenesis.

Nicotinic receptors in Lymnaea stagnalis neurons are blocked by alpha-neurotoxins from cobra venoms.

The influence of cobra neurotoxins on the Cl-dependent responses to acetylcholine (ACh) of Lymnaea neurons was studied by the voltage-clamp technique. It was found that a short chain neurotoxin II (NT II), a long chain cobratoxin (CTX) and weak neurotoxin (WTX) diminished the ACh-induced currents, the block being concentration-dependent and competitive. The IC(50) values of 130 nM for CTX, 11 microM for NT II, and 67 microM for WTX were determined. The block induced by NT II was quickly reversible upon toxin washout, whereas the action of CTX and WTX was only partially reversible even after an hour of intensive washing. The data obtained suggest that acetylcholine receptors (AChRs) in Lymnaea neurons have common features with cation-selective alpha 7 AChRs of vertebrates and one type of Aplysia Cl-conducting AChRs.

Intracellular Ca2+ modulates Cl- current evoked by acetylcholine in Lymnaea neurons.

The influence of voltage-gated Ca2+ current (ICa) on Cl current (ICl) initiated by nicotinic receptors (AChRs) in dialysed voltage-clamped Lymnaea neurons was studied. Depolarising steps applied before or during ACh application decreased ICl transiently and slowed down both the rising phase and decay of ICl. The effect of ICa depended on the interval between ICa and ICl; it was prevented by intracellular buffering with BAPTA or Ca2+ channel blocking with Ni2+. ISr had a similar action but the recovery was slower than after ICa; IBa was ineffective. The data suggest that inactivation of AChR channels is mediated by Ca2+ binding to a site in the AChR or the regulatory protein.

Intracellular ATP modifies the voltage dependence of the fast transient outward K+ current in Lymnaea stagnalis neurones.

1. The action of intracellular ATP on the fast transient outward K+ current (A-current) was studied in dialysed voltage-clamped Lymnaea stagnalis neurones. 2. When introduced intracellularly in millimolar concentrations ATP caused a shift of the steady-state inactivation curve along the voltage axis in the direction of positive potentials and decreased A-current at all test voltages. 3. Intracellular treatment with an inhibitor of ATP synthesis, sodium arsenate, led to the opposite changes. The action of arsenate was not reversed upon its removal. After wash-out of arsenate ATP restored the initial voltage dependence. 4. Addition of Mg2+ to the solution weakened the action of ATP in proportion to the Mg2+: ATP concentration ratio. On the other hand, in neurones pretreated with arsenate, Mg2+ did not affect the ATP action. 5. When a mixture of glycolytic substrates was applied after arsenate wash-out the activation and inactivation curves shifted towards positive voltages. A substrate of oxidative phosphorylation was ineffective in the same conditions. 6. Non-hydrolysable analogues of ATP, adenosine-5'-O-gamma-thiotriphosphate and adenylyl imidodiphosphate, did not mimic the ATP action. This means that the ATP effect is mediated by some enzymatic process(es). 7. Elevation of total cytosolic Ca2+ concentration as well as intracellular application of agents increasing intracellular free Ca2+ reduced A-current amplitude but failed to alter its voltage dependence. Therefore, ATP action cannot be related to activation of Ca2+ transport. 8. Treatment of the neurones with alkaline phosphatase evoked a shift of the inactivation voltage dependence towards hyperpolarizing potentials and increased the A-current amplitudes at all test voltages. 9. The data indicate that a change in intracellular ATP concentration modulates the A-current voltage dependence. The effect of ATP is probably the result of phosphorylation of a channel protein or some associated proteins, but lowering of free Mg2+ concentration cannot be excluded. The possible physiological significance of the phenomenon is discussed.

Hypometabolic and hypothermic factors from small intestine of hibernating ground squirrels (Citellus undulatus).

Low molecular mass components of the acetic acid extract from the small intestine of hibernating ground squirrels (Citellus undulatus) produced a decrease in oxygen consumption and body temperature of white mice and a dose-dependent delay in embryonic development of sea urchin (Strongylocentrotus intermedius). Equivalent doses of low molecular mass components obtained by the same method from active (summer) animals did not have such an effect.

[Embryonic development of the sea urchin after low-temperature preservation]. / Razvitie zarodyshei morskogo ezha posle nizkotemperaturnoi konservatsii.

The sea urchin embryos were cooled to -196 degrees by two-step freezing with the use of 1-1.5 M dimethyl sulfoxide as a cryoprotectant. The embryos were equilibrated with the cryoprotectant for 20-30 min at 0 +/- 2 degrees. At -7 degrees ice crystallization was induced and the embryos were cooled to -38-42 degrees at a rate of 6-8 degrees /min. The embryos were then transferred into liquid nitrogen. The embryos were thawed in a water bath at 19 degrees. No less than 90% of the embryos frozen at the stages of blastula, gastrula, or pluteus were capable of recovery and normal development. The length of cryopreservation did not affect the survival of the embryos.