Biomedical subjects
Publications and source records attributed to G Haudecoeur.
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Agents such as TEA+ or CS+ ions, these last ions instead of K+ ions in poor K extracellular solution, known to reduce or abolish the inwardly rectifying channel in many preparations produced no effect in crayfish muscle membrane By contrast, poor Cl extracellular solution (Cl- ions were replaced by CH3OSO3- ions) blocked the inward current activated by hyperpolarizing pulses and produced an increase of the resting potential. Niflumic acid is a agent which inhibited the inward going rectification of the crayfish muscle membrane. Apparent dissociation constant of niflumic acid with membrane sites was equal to about 6 X 10(-8) M; this value corresponds to that given by Cousin & Motais (1979) concerning translocation of Cl- ions in the membrane of red cells. Activation of the inward going rectification in the crayfish membrane is responsible of an inward current carried by Cl- ions.
ATP hydrolysis-pCa and isometric tension-pCa relationships were determined for isolated myofibrils under a variety of ionic conditions i.e. in presence of Cl- ions (normal conditions), in presence of CH3COO- or CH3OSO3- (ions replacing all or a part of Cl- ions). In all ionic conditions, these relationships have a S-shape. For each ionic condition, the relationships between isometric tension or ATP hydrolysis and pCa were parallel, but the isometric tension-pCa was shifted towards a smaller value of pCa. The relation between ATP hydrolysis and pCa has been analysed by means of the enzymatic reaction described by Michaelis-Menten. The analysis of isometric tension-pCa relationship can be also described by using the consecutive scheme of reaction for the co-operative action of two Ca2+ ions in the process of tension activation given by Ashley & Moisescu (1977) for barnacle myofibrils. The dissociation constant (k1) equal to the one that we determined for the ATP hydrolysis probably corresponds to the Ca2+ binding site of troponin (M1). This association (M1-Ca) would lead to the phosphorylation of the second site (M2) localized on myosin, which can bind a Ca2+ ion. In presence of CH3COO-, ATP hydrolysis (V) was increased with no change of the affinity of the first site for the Ca2+ ion. At the opposite, V did not change but the affinity of M1 site was decreased in presence of CH3OSO3-. CH3OSO3- must be considered as a competitive inhibitor whereas CH3COO- must be considered as an activator ion of the ATP hydrolysis reaction. In all cases, the relationship between isometric tension and ATP hydrolysis was hyperbolic.
1.--The tetraethylammonium (TEA) effects on K+ contracture and membrane depolarization are compared in both crab and frog skeletal muscle fibres. 2.--The mechanical tension of the contracture is reduced by the TEA in frog skeletal muscle fibre; it is increased in crab skeletal fibre. 3.--When no mechanical phenomenon is observed in frog skeletal muscle, the amplitude and the velocity of membrane depolarization induced by an increase of outward K+ concentration is reduced by the TEA. These effects are in opposition in crab muscle fibre. 4.--In crab muscle fibre, the results obtained tend to show that the C1-ions are not distributed on each side of the membrane according to Donnan equilibrium.
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Experiments were performed to investigate the modifications of electrical activity and the loss of contraction by examination of the ultrastructure. These alterations were obtained with a control physiological solution (artificial sea water, ASW) which was made hypertonic by adding sucrose, glycerol, choline chloride or urea. 1. Under these conditions, the ultrastructural results show that: a) all those substances induce a modification of the coupling junction (either diad or triad). This modification can explain the inhibition of the mechanical phenomenon; b) sucrose (Figs. 6C and 6D) and glycerol (Figs. 4A and 4B) induce alterations of the surface membrane and of the tubular system (less important with glycerol). They can explain the decrease of the resting potential and the abolishment or the modification of the action potential; c) in contrast, choline chloride (Figs. 7A to 7E) and urea (Figs. 9A to 9F) only modify the organisation of the coupling junction. The action potential is maintained. 2. A short exposure of the fibre in an isotonic sucrose solution (Figs. 5A to 5D) deeply modifies the tubular system, particularly, in cutting it off from the sarcolemma. 3. Choline chloride and urea produce similar changes in the ultrastructure but as urea is not ionized, it can be added to the ASW to investigate the electrical phenomenon which cannot be modified by contraction.
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Membrane currents during depolarisation steps were determined by a method in which three electrodes were inserted near the end of the crab's striated muscular fibre. The value of the reversal potential for the early current appears to be consistent with the calcium equilibrium potential. This early transient inward current is abolished by manganese. The value of about +120mV is consistent with the level of internal free Ca++ ions, as generally tested by different authors.
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