Application of adsorption kinetics for estimation of dissociation constants

Substances such as drugs, as well as special ligands with expressive biospecific properties, all with different affinities, interact with proteins which can be characterized by dissociation constants. The method for estimation of the dissociation constant on the basis of adsorption kinetics was verified for two typical cases: adsorption of lactate dehydrogenase onto bead cellulose derivatized by reactive dyes C.I.2. or C.I.19, and adsorption of different drugs (neuroleptics and local anesthetics) onto calmodulin immobilized on agarose gel. The real equilibrium values obtained by using the complete time-concentration model of adsorption were fitted according to the respective adsorption isotherms by non-linear regression.     

Prevention by 7-oxo-prostacyclin of the calcium paradox in rat heart: Role of the sarcolemmal (Na,K)-ATPase

It is demonstrated a fast and significant depression in the sarcolemmal (Na,K)-ATPase activity that occurs as early as 25 sec after the onset of Ca²⁺ depletion, and participates in the development of Ca²⁺-paradox in the rat heart. Pretreatment of the animals with 7-oxo-prostacyclin (PG12) 24–48 h prior to the experiment prevented fairly the Ca²⁺-depletion-induced depression in (Na,K)ATPase activity and the accompanying structural and functional damage to the heart and sarcolemma during Ca²⁺-depletion as well as the development of Ca²⁺-paradox during the subsequent Ca²⁺-repletion. Pretreatment with PGI, was chosen intentionally because previous experiments revealed, that in its late effect the drug is acting via stabilizing the membranes due induction of high activity of (Na,K)-ATPase that has increased affinity to ATP. From results obtained the following may be concluded: If during the phase of Ca²⁺-deprivation, the capability of heart sarcolemma to maintain sodium extrusion remains preserved, the expected aggravation of Ca²⁺-overload injury to Ca²⁺-paradox that would develop during Ca²⁺-repletion, may be definitely prevented. Sufficiently preserved (Na,K)-ATPase activity, hand in hand with stabilized sarcolemmal structure, may prevent an accumulation of sodium beneath the sarcolemma and consequently also an overexcessive entry of Ca²⁺ into the myocytes.