Age dependency of [ 3 H]-ouabain binding, 45 Ca 2? eflux and its magnetosensitivity in rats' brain cortex and heart muscle tissues were studied. Curves of dose-dependent [ 3 H]-ouabain binding consisted of three components with different affinities (10 -7 -10 -4 M (a 1 ); 10 -9 -10 -7 M (a 2 ); and 10 -11 -10 -9 M (a 3 )). These curves were also characterized by different dose-dependent kinetics. [ 3 H]-ouabain binding with a 3 receptors in brain cortex and heart muscle tissues of young and adult animals had a dose-dependent character, while that in old ones had a doseindependent character. A 0.2 T static magnetic field (SMF) exposure had modulation effect on ouabain binding with a 1 , a 2 and a 3 receptors in young rats, while in adult ones, only a 3 receptors were magnetosensitive. In old animals, SMF exposure had no significant effect on ouabain binding with a 3 receptors in brain cortex, while in heart muscle, it had inhibitory effect on it. Age-dependent effect of ouabain impact on 45 Ca 2? efflux showed that all concentrations of ouabain lead to inhibitory effect in young animals' brain cortex and heart muscle (with the exception of 10 -10 and 10 -6 M), while in old ones, it had activation effect as compared with data received without ouabain. SMF exposure in young animals had activation effect on 45 Ca 2? efflux from brain cortex and heart muscle in data without ouabain, and in old rats, 45 Ca 2? efflux from brain cortex was magnetic insensitive. In old animals, SMF increased 45 Ca 2? efflux even after extra low concentration of ouabain. It is suggested that a 3 receptors having a crucial role in the regulation of Na ? /Ca 2? exchange serve as age-dependent magnetosensors of excitable cells.

The reason for hyper magnetosensitivity of young animals compared to older ones remains unclear. It has been suggested that age-induced tissue dehydration (decreased water content) could be a basis for the aging-related decrease in the organism's magnetosensitivity. To test this hypothesis, the effect of a 0.2 T static magnetic field (SMF) exposure on heart muscle hydration in three age groups of rats (young, adult, and older) was studied, with and without ouabain poisoning. The SMF exposure resulted in heart muscle dehydration of young (21%) and adult (6.2%) rats but had no effect on older animals. In young animals without ouabin poisoning, SMF exposure caused dehydration of the heart muscle while in the ouabain-poisoned animals it led to hydration (29.6%). These hydration effects were more pronounced in young animals than in adult and older animals. The increased hydration (5.7%) of heart muscles in older animals was evoked by providing distilled water for seven days, which elevated (by 12%) the SMF-induced heart muscle hydration effect. These results suggest that the hyper magnetosensitivity of the young heart muscle and the lower sensitivity of older animals are due to initial high (83.5%) and low (75.3%) tissue hydration levels, respectively. Therefore, the age-induced decrease in the magnetosensitivity of heart muscle is likely to be a result of Na(+)/K(+) pump dysfunction.

In our previous work we have shown that the age-dependent decrease in the magnetosensitivity of heart muscle hydration is accompanied by a dysfunction of the Na(+) /K(+) pump. The reciprocal relation between the Na(+/) K(+) pump and Na(+) /Ca(2+) exchange in development was suggested as a possible pathway for the age-dependent decrease in the magnetosensitivity of heart muscle hydration (water content). Because high and low affinity ouabain receptors in cell membranes are involved in Na(+) /Ca(2+) exchange and Na(+) /K(+) pump functions, respectively, the effect of a 0.2 T static magnetic field (SMF) on dose-dependent, ouabain-induced hydration and [(3) H]-ouabain binding with heart muscle tissues in young, adult and older rats was studied. Three populations of receptors in membranes with high (10(-11) -10(-9)  M), middle (10(-9) -10(-7)  M) and low (10(-7) -10(-4)  M) affinity to [(3) H]-ouabain were distinguished, which had specific dose-dependent [(3) H]-ouabain binding kinetics and effects on muscle hydration. The magnetosensitivity of [(3) H]-ouabain binding kinetics with high affinity receptors was prominent in all the three age groups of animals, while with low affinity receptors it was more expressed only in the young group of animals. All three types of receptors that caused modulations of muscle hydration were age dependent and magnetosensitive. Based on the obtained data we came to the conclusion that heart muscle hydration in young animals is more magnetosensitive due to the intense expression of high affinity ouabain receptors, which declines with aging.

Previously, we have suggested that cell hydration is a universal and extra-sensitive sensor for the structural changes of cell aqua medium caused by the impact of weak chemical and physical factors. The aim of present work is to elucidate the nature of the metabolic messenger through which physiological solution (PS) treated by non-thermal (NT) microwaves (MW) could modulate heart muscle hydration of rats. For this purpose, the effects of NT MW-treated PS on heart muscle hydration, [H]-ouabain binding with cell membrane, Ca uptake and intracellular cyclic nucleotides contents in vivo and in vitro experiments were studied. It is shown that intraperitoneal injections of both Sham-treated PS and NT MW-treated PS elevate heart muscle hydration. However, the effect of NT MW-treated PS on muscle hydration is more pronounced than the effect of Sham-treated PS. In vitro experiments NT MW-treated PS has dehydration effect on muscle, which is not changed by decreasing Na gradients on membrane. Intraperitoneal injection of Sham- and NT MW-treated PS containing Ca have similar dehydration effect on muscle, while NT MW-treated PS has activation effect on Na/Ca exchange in reverse mode. The intraperitoneal injection of NT MW-treated PS depresses [H]-ouabain binding with its high-affinity membrane receptors, elevates intracellular cAMP and decreases cGMP contents. Based on the obtained data, it is suggested that cAMP-dependent signaling system serves as a primary metabolic target for NT MW effect on heart muscle hydration.

The elucidation of the mechanism on the biological effects of weak chemical and physical factors on cells and organism is one of the modern problems in life sciences. According to the Receptor Theory of Prof. Bernard Katz the impact of the biological substances on cells is realized through the activation of ligand-gated ion channels in the membrane. However, this theory doesn't provide a satisfactory explanation on the similar biological effects of extremely low concentrations of different chemical substances, which are unable to activate the ionic channels in the membrane and have non-linear dose-dependent effect on cells. Previously we have suggested that the metabolic control of cell hydration serves as a universal quantum-mechanical sensor for different weak physical and chemical signals. For supporting this hypothesis, in this article the comparative study of the effects of low concentrations of both cold (non-radioactive) and [ 3 H]-ouabain (specific inhibitor for Na + /K +-ATPase) on the hydration in different tissues of rats has been performed. The obtained data have shown that cold and [ 3 H]-ouabain have different effects on cell hydration and such a difference depends on the initial metabolic state of tissues. On the basis of our previous and present results it is suggested that such a quantum-mechanical sensitivity of cell hydration is realized through the cyclic-nucleotides-dependent Na + /Ca 2+ exchange, having a crucial role in the metabolic regulation of cell hydration.