Effects of ethylene glycol on the kinetics of contraction on flash photolysis of caged ATP in rat psoas muscle fibres

Crossbridge kinetics in single frog muscle fibres in presence of ethylene glycol

Single fibres isolated from frog muscle were tetanically stimulated at 14 degrees C to produce isometric tetani at a sarcomere length of about 2.16 microm, using a striation follower device to measure the sarcomere length of a selected segment of fibre. Force-velocity data were obtained by applying ramp releases at pre-set velocity at the tetanus plateau. Sarcomere stiffness was measured at isometric plateau and during isotonic shortening by using sinusoidal length changes at 2 kHz frequency and about 1 nm per half sarcomere (hs) peak to peak amplitude. A correction method was used to compensate for the force truncation due to the quick recovery. After data collection, the bathing solution was substituted with Ringer plus ethylene glycol (EG) at 2 M (11.2% v/v). When the fibre was fully equilibrated with the new solution, the measurements were repeated. Ethylene glycol reduced the speed of the tetanus rise and tetanus relaxation without altering the isometric tension, and reduced the maximum shortening velocity by about 20%. During isotonic contraction tension and stiffness at each given shortening velocity were reduced by about the same amount, so that the stiffness/tension ratio remained almost unaltered. Force-velocity and stiffness data in both standard and EG Ringer were analysed in terms of a two state model (Huxley, 1957). The analysis showed that our results can be accounted for by assuming that EG at 2 M concentration reduces all the rate constants for crossbridges interaction by about the same amount.

Ethylene Glycol Dimethacrylate Cross-linking Anion Exchange Resin as Phosphate Binder: Effects on Rat gut and Digestion by Small Intestine Contents

In the present study, ethylene glycol dimethacrylate cross-linking 4-vinylpyridinium anion exchange resin (EGDMA-4VP) effectively bound dietary phosphate in normal rats. However, EGDMA-4VP induced more adverse effects in rat gut than cellulose or Dowex 1X2 (both of which have higher water content), and caused damage to the intestine. In order to resolve this seeming paradox, digestion of EGDMA-4VP with rat small intestine content (S-9 fraction) and carboxyl esterase was investigated in vitro to examine the stability of the resin under conditions it would be subjected to as an orally administered medicine. EGDMA-4VP was digested by small intestinal enzymes, with the exception of carboxyl esterase, and the degradation product ethylene glycol (EG) caused reversible relaxation of longitudinal muscle (but not circular muscle) in rat small intestine. Degradation products increased uptake of3H2O into primary cultured rat small intestinal muscle cells, but the increase was not significant.

Probing the coupling of Ca2+ and rigor activation of rabbit psoas myofibrillar ATPase with ethylene glycol

We have exploited solvent perturbation to probe the coupling of Ca2+ and rigor activation of the ATPase of myofibrils from rabbit psoas. Three techniques were used: overall myofibrillar ATPases by the rapid-flow quench method; kinetics of the interaction of ATP with myofibrils by fluorescence stopped-flow; and myofibrillar shortening by optical microscopy. Because of its extensive use with muscle systems, ranging from myosin subfragment-1 to muscle fibres, we chose 40% ethylene glycol as the relaxing agent. At 4 degrees C, the glycol had little effect on the myofibrillar ATPase at low [Ca2+], but at high [Ca2+] the activity was reduced 50-fold, close to the level found under relaxing conditions, and there was no shortening. However, the ATPase of chemically cross-linked myofibrils (permanently activated even without Ca2+) was reduced only 3-4-fold. The lesser reduction of the ATPase of permanently activated myofibrils was also observed in single turnover experiments in which activation occurs by a few heads in the rigor state activating the remaining heads. The addition of ADP, which also promotes strong head-thin filament interactions, also activated the ATPase but only in the presence of Ca2+. Further experiments revealed that in 40% ethylene glycol, Ca2+ does initiate shortening but only with the aid of strong interactions and at temperatures above 15 degrees C. This confirms that in the organized and intact myofibril, Ca2+ and rigor activation are coupled, as proposed previously for regulated actomyosin subfragment-1.

Ethylene glycol poisoning: case report of a record-high level and a review

Ethylene glycol is commonly found in automobile antifreeze and a variety of other commercial products. Ingestion of ethylene glycol, either accidentally or in a suicide attempt, is characterized by severe acidosis, calcium oxalate crystal formation and deposition, and a wide variety of end organ effects that may be fatal. We present a case of a patient who ingested a massive amount of ethylene glycol in a suicide attempt and yet survived with minimal sequelae. A comprehensive review of the literature on the pathology and pathophysiology of ethylene glycol toxicity on each organ system is provided, along with information on diagnosis and current treatment recommendations.

Mechanical study of rat soleus muscle using caged ATP and X-ray diffraction: high ADP affinity of slow cross-bridges

1. The cross-bridges in slow- and fast-twitch fibres (taken, respectively, from soleus and psoas muscles of rats) were examined in mechanical experiments using caged ATP and X-ray diffraction, to compare their binding of ATP and ADP. 2. Caged ATP was photolysed in rigor fibres. When ADP was removed from pre-photolysis fibres, the initial relaxation (+/- Ca2+) in soleus was as fast as that in psoas fibres, whereas the subsequent contraction (+Ca2+) was slower in soleus than in psoas. The ATPase rate during the steady-state contraction was also slower in soleus fibres. 3. When ADP was added to pre-photolysis fibres (+/- Ca2+), tension developed even in the initial phase, the overall tension development being biphasic. Both initial and late components of the Ca(2+)-free contraction were enhanced when ADP was added before photolysis, although pre-photolysis ADP was not a prerequisite for the late component. The effect of ADP was greater in soleus than in psoas fibres. Static experiments on rigor fibres revealed a higher ADP affinity in soleus fibres. 4. The intensity of the actin layer-line from ADP rigor soleus fibres decreased rapidly on photorelease of ATP. We conclude that, despite the tight ADP binding of the soleus cross-bridge, its isometric reaction is not rate limited by the 'off' rate of ADP.

Tension relaxation induced by pulse photolysis of caged ATP in partially crosslinked fibers from rabbit psoas muscle

Muscle contractile force is thought to be generated by ATP-induced conformational changes in myosin crossbridges. In the present study, we investigated the response to ATP binding of force-bearing, attached cross-bridges. For this investigation, skinned fibers, in which myosin heads were in part covalently crosslinked to thin filaments with a zero-length crosslinker, were prepared. Caged ATP [the P3-1-(2-nitro)phenylethyl ester of ATP] was then pulse-photolyzed in these crosslinked fibers, which retained ATP-induced "rigor" tension, and then the subsequent tension changes were followed at 14-16 degrees C and ionic strengths of 0.1-2 M. A rapid tension decrease was observed after the photolysis in the partially crosslinked fibers. The rate of the decrease was not any different from that in the uncrosslinked fibers compared at ionic strength of 0.2 M. This and other results thus indicate a kinetic similarity in the crosslinked and uncrosslinked crossbridges in response to ATP binding. These findings also suggest that ATP-induced structural changes take place in the attached crossbridges at a rate similar to that of the ATP-induced dissociation of crossbridges from thin filaments.

Transient contraction of muscle fibers on photorelease of ATP at intermediate concentrations of Ca2+

We isometrically activated skinned fibers in rigor by flash photolysis of caged ATP at various [Ca2+] at 8 degrees C. On release of ATP, tension initially decreased with the same time course at all [Ca2+]. At high [Ca2+] (pCa < or = 5.8), tension rose to the steady-state plateau after the brief relaxation. When the [Ca2+] was intermediate (7.0 < or = pCa < or = 6.0), tension temporarily overshot the final steady-state level. The half-time during this tension transient was longer at higher [Ca2+]. The transient contractions could be simulated by a simple kinetic model: R + ATP-->Q, and X<-->Q<-->A, where R, X, and A are the rigor, relaxed, and active-tension states, respectively; Q is a "pre-active" state where tension is very low; and Ca2+ affects only the X-Q transition. This scheme was also useful for predicting the tension transients in Ca(2+)- and P(i)-jump experiments at various [Ca2+]. ADP enhanced the Ca2+ sensitivity of the ATP-induced transient contraction, which was not in the scope of the model.

Mechanical response to photolytic ATP pulses of skinned muscle fibres pre-activated with a small pulse of ATP

(1) Skinned fibres from rat psoas muscle were placed in oil and activated at 10 degrees C by pulse photolysis of caged ATP. From the force and stiffness transients on small ATP pulses, we estimated the concentration and rate of ATP hydrolysis of the crossbridges in the fibres. They were 0.14 mM and 0.16 mMs-1, respectively, and thus the turnover rate was 1.1 s-1. (2) To examine the mechanical properties of the physiological ADP-bound crossbridges, we took a double-pulse protocol: the skinned fibre was first activated with a conditioning ATP pulse (0.2-0.5 mM). Several (3-5) seconds later, when almost all the ATP should have been hydrolysed into ADP+P(i), we applied another ATP pulse (0.2-1 mM) to test the fibre. (3) An analysis of the transients on the test pulses indicated that the conditioning pulse slowed the rate of crossbridge detachment. The time course of force development was thus expected to be also delayed, but was not. (4) We suggested that the rigor crossbridge might differ from the nucleotide-free intermediate in the physiological reaction cycle.

Time-resolved electron microscopic analysis of the behavior of myosin heads on actin filaments after photolysis of caged ATP

The interaction between myosin subfragment 1 (S1) and actin filaments after the photolysis of P3-1-(2-nitrophenyl)ethyl ester of ATP (caged ATP) was analyzed with a newly developed freezing system using liquid helium. Actin and S1 (100 microM each) formed a ropelike double-helix characteristic of rigor in the presence of 5 mM caged ATP at room temperature. At 15 ms after photolysis, the ropelike double helix was partially disintegrated. The number of S1 attached to actin filaments gradually decreased up to 35 ms after photolysis, and no more changes were detected from 35 to 200 ms. After depletion of ATP, the ropelike double helix was reformed. Taking recent analyses of actomyosin kinetics into consideration, we concluded that most S1 observed on actin filaments at 35-200 ms are so called "weakly bound S1" (S1.ATP or S1.ADP.Pi) and that the weakly bound S1 under a rapid association-dissociation equilibrium with actin filaments can be captured by electron microscopy by means of our newly developed freezing system. This enabled us to directly compare the conformation of weakly and strongly bound S1. Within the resolution of deep-etch replica technique, there were no significant conformational differences between weakly and strongly bound S1, and neither types of S1 showed any positive cooperativity in their binding to actin filaments. Close comparison revealed that the weakly and strongly bound S1 have different angles of attachment to actin filaments. As compared to strongly bound S1, weakly bound S1 showed a significantly broader distribution of attachment angles. These results are discussed with special reference to the molecular mechanism of acto-myosin interaction in the presence of ATP.

Effects of ionic strength on force transients induced by flash photolysis of caged ATP in covalently crosslinked rabbit psoas muscle fibers

Single fibers from glycerinated rabbit psoas muscle were treated with 1-ethyl-3[3-(dimethylamino) propyl] carbodiimide (EDC), after rigor was induced, to crosslink myosin heads to actin. The optimally pre-stretched (approximately 1.8%), partially crosslinked fibers produce a large force when MgATP is depleted, and this force is abolished when MgATP is reintroduced, even in high ionic strength solution of 0.5 M (Tawada et al. 1989). We investigated the rate of force decay in the crosslinked, force-producing fibers using pulse photolysis of caged ATP (Goldman et al. 1984). The decay of force was fast, the rate of which depending both on the ionic strength and on the amount of ATP released (0.2-2.2 mM) with the second-order rate constant of 0.5-1 x 10(5) M-1s-1 at the ionic strength of 0.5 M. At high ionic strength (1-2M) force decayed at lower rate. At low ionic strength (0.1-0.2 M), however, force decayed more rapidly, but force redeveloped subsequently, which is probably caused by uncrosslinked myosin heads.

Time course of rise of muscle stiffness at onset of contraction induced by photorelease of ATP

Isometric contraction (9-10 degrees C) of skinned fibres from rat psoas muscle was elicited by photorelease of ATP (1.3-1.4 mM), and force (F), in-phase (I) and quadrature (Q) stiffness were monitored. The sinusoidal length change for the stiffness measurement was approximately 0.09% fibre length and 200-1000 Hz. On photolysis, F and I initially fell, and then rose. The half-time of the rise of I was shorter than that of F. Contrary to the previous assumption, Q rose even earlier than I. Although the time courses of the rise of F and I were greatly affected by the presence of phosphate ion (Pi; 4 mM), its effect on Q was modest. We propose the following hypothesis: the rigor crossbridges, after binding ATP, initially enter a state characterized by high Q with low I and none or little F, and then, releasing Pi during passing the state with the increased I, reach the final force generating state.

Effects of ethylene glycol and calcium on the kinetics of contraction induced by photo-release of low concentrations of ATP in rat psoas muscle fibres

To induce isometric contraction in the absence of Ca2+ (10 mM EGTA), low concentrations (130 microM) of ATP were photoreleased from caged ATP in skinned fibres from rat psoas muscle at 15-16 degrees C. The magnitude of contraction was independent of the concentration of EGTA (1-30 mM). Each isometric transient (i) was paired with another (s) obtained under the same conditions but with 0.4% muscle stretch to elevate the rigor force before photolysis. The algebraic difference (d) between i and s was assumed to represent detachment of the crossbridges. The time course of force development (f) by the reattached crossbridges could be estimated by subtracting an appropriately scaled d from i (or s). Ethylene glycol (20% in solvent) reduced the magnitude and the rate of rise of f, although it scarcely affected d, suggesting that ethylene glycol inhibited reattachment of the crossbridges but not their detachment. The presence of Ca2+ (50 microM) increased the magnitude of f, but did not affect its time course (130 microM ATP). Detachment, d, was not influenced by Ca2+ in terms of both extent and rate. The effect of Ca2+ in the presence of ethylene glycol was indistinguishable from that in its absence. Ethylene glycol did not seem to substantially affect the extent of Ca-regulation on the contractile activity.