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PubMed1979

Biochemical and physiological studies of long-term synaptic plasticity.

High frequency stimulation of fiber systems in the mammalian hippocampus produces a semipermanent increase in synaptic efficacy. This effect, long-term potentiation (LTP), has been of considerable interest as a potential substrate of memory due to its rapid onset and extreme persistence. Experiments are described that indicate that the locus of LTP is confined to the synaptic complex of the fibers stimulated; further, Ca2+ is shown to be essential for the initiation of LTP and may play a role in triggering this increase in synaptic efficiency. Data from biochemical analyses of LTP indicate that a 40,000 dalton synaptic membrane protein shows a highly reliable change in its endogenous phosphorylation following high frequency hippocampal stimulation. Phosphorylase kinase, a Ca2+ sensitive enzyme, is shown to specifically catalyse the phosphorylation of this 40,000 dalton protein. The data are discussed in terms of a working model in which the Ca2+ dependent phosphorylation of the 40,000 dalton protein produced by high frequency stimulation is a biochemical intermediate in the production of LTP.

Animals↗
PubMed1985

[Mechanisms of involvement of Na+(Li+) in the process of intracellular transmission of the trigger signal in skeletal muscles].

The data obtained suggest that Li+ can replace Na+ in transmission of triggering signal from excited surface membrane of muscle fibers onto intracellular effector systems. The participation of extracellular calcium in transmission of activation into the cell being excluded, the Ca2+-activation of the contractile apparatus and kinase-phosphorylase system in electrically stimulated muscles presumably proceeds from the induction of Ca2+ release from sarcoplasmic reticulum (SR) by transmembrane Na+- or Li+-current. The chemical specific features of Na+ and Li+ displayed at that, corroborate the hypothesis of Na+-trigger mechanism of Ca2+ release from the SR in skeletal muscle fibers of vertebrates.

Animals↗
PubMed1984

Agonist and antagonist properties of calmodulin fragments.

Limited proteolysis of calmodulin with trypsin in the presence of ethylene glycol bis(beta-aminoethyl ether)-N, N,N',N'-tetracetic acid (EGTA) or Ca2+ was performed according to a modification of the method of Drabikowski et al. (Drabikowski, W., Kuznicki, J., and Grabarek, Z. (1977) Biochim. Biophys. Acta 485, 124-133). The resulting peptides were purified by reverse-phase high performance liquid chromatography. Tryptic digests in EGTA yielded peptides 1-106, 1-90, and 107-148 with yields of 9, 47, and 61%, respectively. The digests performed with Ca2+ yielded peptides 1-77 and 78-148 in 35 and 45% yield. Analysis by high performance liquid chromatography indicated that the purified fragments contained less than 0.1% contamination by calmodulin, thus allowing a definitive study of the ability of these fragments to activate, or interact with, calmodulin-regulated enzymes and anti-calmodulin drugs. Each of the fragments, except 107-148, bound to a phenothiazine affinity column in a Ca2+-dependent manner. Thus, calmodulin contains two interaction sites for phenothiazines: one on the NH2-terminal half (fragment 1-77) and one on the COOH-terminal half (fragment 78-148). None of the fragments activates the protein phosphatase, calcineurin, or prevents its stimulation by calmodulin, nor does any of the fragments stimulate Ca2+-dependent cAMP phosphodiesterase. A single cleavage in the middle of the calmodulin molecule results in the rapid dissociation of the two resultant fragments and a loss of ability to activate cAMP phosphodiesterase. One fragment, 78-148, interacts with phosphodiesterase and prevents its activation by calmodulin (Ki: 1.5 +/- 0.4 X 10(-6) M). The same fragment, 78-148, can fully activate phosphorylase kinase but with a lower affinity than calmodulin (Kuznicki, J., Grabarek, Z., Brzeska, H., Drabikowski, W., and Cohen, P. (1981) FEBS Lett. 130, 141-145). Thus, peptide 78-148 behaves as a calmodulin agonist or antagonist or as neither, depending on the enzyme under study.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Bioenergetics of intact human muscle. A 31P nuclear magnetic resonance study.

The metabolic state of human muscle in various functional states has been investigated by the non-invasive technique of 31P nuclear magnetic resonance. The concentrations of phosphocreatine, ATP and inorganic phosphate as well as intracellular pH in the flexor digitorum superficialis have been measured during rest, dynamic exercise and recovery from exercise. The observed relationship between phosphocreatine utilization and decrease in intracellular pH during aerobic exercise indicates that lactate production only becomes significant after more than 60% of the phosphocreatine is used up. Surprisingly intracellular pH may reach as low a value as 5.9 to 6.1, indicating that phosphofructokinase is still partially active at pH 6.0. There is no metabolic recovery if the muscle is made ischaemic following exercise, implying that glycolysis is switched off as soon as exercise is stopped. Lactic acidosis is not the cause of this and presumably Ca2+ is needed to maintain the activation of phosphorylase kinase. The time-course of phosphocreatine recovery after exercise reflects the rate of oxidative metabolism, while pH recovery probably represents H+ ion export from the muscle cell. The dynamics of metabolic changes can now be observed with a time resolution of 10 to 60 seconds and thus disturbances in energy metabolism can be readily detected in several pathological states.

Adenosine Diphosphate↗