Biomedical subjects
Publications and source records attributed to N I Pokudin.
Na+/H+ exchange rate in erythrocytes of patients with atherosclerosis of lower limb arteries is less than in erythrocytes of healthy subjects. Ultraviolet exposure of the patients blood in vitro activates Na/H exchange in erythrocytes.
Ca binding in the red blood cell (RBC) membrane of spontaneously hypertensive rats (SHR) and of patients with essential hypertension was studied. Under conditions of physiological concentration of free Ca in the incubation medium of RBC the outer part of the membrane binds 393 +/- 32 and 435 +/- 30 nmole of Ca per ml of RBC in rats and humans, respectively, without essential differences in the amount of Ca in hypertensive individuals as compared to the normotensive controls. The membrane of red blood cell ghosts (RBCgh) at concentrations of free Ca corresponding to its intracellular concentration binds 4.28 +/- 0.39 and 3.53 +/- 0.15 nmole of Ca per mg of protein of RBCgh in rats and humans, respectively. This part of membrane-bound Ca pool (most probably related to the inner part of the red blood cell membrane) is reduced by 48% in SHR and by 28% in patients with essential hypertension as compared to normotensive controls. It is suggested that the decrease of Ca binding ability of the RBC membrane in both types of hypertension studied may be a pattern of a more widespread cell membrane defect.
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Studies of the effects of luliberin (luteinizing hormone-releasing hormone) on cardiac cells showed that the hormone is specifically bound by the sarcolemmal membrane. The activity of the membrane enzyme -- reception of luliberin involves two types of binding sites with high (K' = 10(7) M-1) and low (K'' = 10(5) M-1) affinities for the hormone, respectively. The hormone has no effect on the activities of adenylate cyclase and phosphodiesterase.
The basal content of cAMP and cGMP in isolated adipose cells of rats with spontaneous genetic hypertension (SHR) was studied. No differences were found between SHR rats and animals with normal pressure in the content of cyclic nucleotides. Adrenalectomy changes essentially the content of cAMP and cGMP in the adipocytes, reducing the cAMP/cGMP ratio in the cells to about one half; the content of cAMP and cGMP is greater in the adipocytes of adrenalectomized SHR rats than in those of adrenalectomized animals with normal pressure.
Using the isotope exchange technique including 45Ca, the Ca2+-binding and Ca2+-accumulating capacity of mitochondria, sarcolemma and sarcoplasmic reticulum of rat heart was studied. The ATP-independent binding of Ca2+ to isolated membrane fractions is by 1--2 orders of magnitude less than the ATP-dependent Ca2+-accumulating capacity of the fractions. The Ca2+-accumulating capacity of mitochondria is increased 6--8 fold after addition of physiological concentrations of succinate and Pi to the incubation medium. Under these conditions the ratio of Ca2+-accumulating capacity of mitochondria, sarcolemma and sarcoplasmic reticulum of the heart is 100:3,12:2,9. The initial rate of Ca2+-uptake by the sarcoplasmic reticulum is much higher in comparison with sarcolemma and mitochondria. A high Ca2+-accumulating capacity of heart mitochondria probably determines a long-term regulation of the concentration of "troponin-accessible" Ca2+ in the sarcoplasm, whereas the high initial rate of Ca2+ accumulation by the sarcoplasmic reticulum provides for a rapid decrease of Ca2+ concentration during rhythmic contractions of the heart.
As compared to fatty tissue cells of animals with normal pressure, those of SHR rats were found to be characterized by a higher lipolytic response and a larger increase in the cAMP content on exposure to the effect of ACTH. As compared to the controls, adrenalectomized SHR rats had an increased basal cAMP content and an increased lipolytic response of the adipocytes following adrenaline administration. In inhibition of phosphodiesterase in the fatty cells of adrenalectomized rats with normal pressure, the cAMP content grew by 20% as compared to that in SHR rats subjected to the operation. It is suggested that the changes in intracellular distribution of calcium, shown in this model of hypertension, may be the direct cause of the altered sensitivity of the "target" cells to the effect of hormones.
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Under conditions of physiological concentration of free calcium in the incubation medium (Ca2+f = 1.5 mM), the outer surface of the membrane of human and Wistar rat erythrocytes binds 435 +/- and 359 +/- 32 nmol calcium per 1 ml cells, respectively. The external surface of erythrocytes in patients with essential hypertension and in rats with spontaneous hypertension (SHR, Kyoto Wistar) also binds such amounts of calcium. With the concentration of calcium corresponding to its concentration in the intracellular space (Ca2+f less than 1 mcM), the inner membrane surface of eritrocyte ghosts binds only 3.53 +/- 0.16 and 4.28 +/- 0.39 nmol calcium per 1 mg protein of human and rat eritrocyte ghosts, respectively. The noted decrease in the calcium-binding capacity of the inner part of the erythrocyte membrane, being probably a characteristic feature of membrane alteration displayed also in other cellular structure, may determine the changes in tissue sensitivity to the effect of hormones and catecholamines in both types of hypertension.