Changes in thin filament structure induced by Ca(2+) binding to troponin and subsequent strong cross-bridge regulate additional attachment, force development, dependence of on sarcomere length skeletal cardiac muscle. Variations activation properties account for functional differences between these muscle types.

The maximal calcium-activated isometric tension produced by a skinned frog single muscle fiber falls off as the ionic strength of solution bathing this is elevated declining to zero near 0.5 M varied using KCl. When other neutral salts are used, always declines at high strength, but there some difference between various used. anions and cations can be ordered in terms their ability inhibit tension. order increasing inhibition (decreasing tension) for propionate(-) approximately SO(4) (--) <...

In frog fast skeletal muscle, we find a decline of twitch, tetanus, and maximum K caffeine contracture tensions as tonicity the bathing solution is increased. The tension independent method producing contraction indicates that major effect hypertonicity directly on contractile probably because increased internal ionic strength. However, there some apparent disruption excitation-contraction (E-C) coupling in solutions made three times normal (3T solutions) since: (a) 3T tetanic to zero from...

Cooperative binding of myosin S-1.ADP to regulated F-actin was previously reported and has been interpreted by a two-state model in which an important source cooperativity is nearest neighbor interactions between the 7-actin.tropomyosin (TM).troponin units (functional units) (Hill, T.L., Eisenberg, E., Greene, L. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3186-3190). It postulated that head-to-tail overlap adjacent TM molecules structural basis interactions. We tested hypothesis examining...

Force (F) and stiffness (K) were measured in glycerinated psoas fibers at various calcium levels with 0, 10, 20, 30 mM orthophosphate (Pi) added to the bathing solutions. The concentrations of solution constituents as follows: 110 potassium, 40 sodium, 4 MgATP, 10 total EGTA, variable amounts MOPS (pH buffer). pH was 7.0, ionic strength 200 mM, temperature degrees C. Calcium established by adding CaCl2. All solutions contained 4% Dextran T-500. Fiber K imposing sinusoidal length changes...

1. We examined the effects of aluminofluoride (AlFx) and orthovanadate (Vi), tightly binding analogues orthophosphate (Pi), on mechanical properties glycerinated fibres from rabbit psoas muscle. Maximum Ca(2+)‐activated force, stiffness, unloaded shortening velocity (Vus) were measured under conditions steady‐state inhibition (up to 1 mM inhibitor) during recovery inhibition. 2. Stiffness was using either step or sinusoidal (1 kHz) changes in fibre length. Sarcomere length monitored...

The binding of the NH2-terminal region troponin T (TnT) to COOH-terminal tropomyosin (Tm) and head-to-tail overlap between Tm molecules is thought provide a pivotal link (Tn) (White, S.P., Cohen, C., Phillips, G.N., Jr. (1987) Nature 325, 826-828). To further explore structure-function relationship TnT, we studied 26,000-dalton TnT fragment (26K-TnT, Ohtsuki, I., Shiraishi, F., Suenaga, N., Miyata, T., Tanokura, M.J. (1984) J. Biochem. (Tokyo) 95, 1337-1342) which corresponds residues 46-259...

The results of work by several investigators indicate that crossbridge attachment serves as a positive feedback mechanism transiently increases the Ca2+ affinity troponin C (TnC) during each normal heartbeat. To monitor structural changes in cardiac isoform TnC (cTnC) associated with binding and muscle, we labeled cTnC sulfhydryl-specific fluorescent probe 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid (IAANS). When IAANS-labeled (cTnCIAANS) was substituted for endogenous TnC,...

We examined the effects of post-stimulus length changes on voltage-clamped, aequorin-injected single muscle fibers from barnacle Balanus nubilus. Extra light (extra calcium) is seen when fiber allowed to shorten (a small percentage) during declining phase calcium transient. The opposite observed stretched. Increasing extent shortening increases amount extra calcium, as does decreasing temperature. probably comes myofilaments and not sarcoplasmic reticulum because (a) there a strong...

Isolated skinned frog skeletal muscle fibers were activated (increasing [Ca2+]) and then relaxed (decreasing with solution changes, force stiffness recorded during the steady state. To investigate actomyosin cycle, biochemical species changed (lowering [MgATP] elevating [H2PO4-]) to populate different states in ATPase cycle. In solutions 200 microM [MgATP], compared physiological slope of plot relative state vs. was decreased. At low cross-bridge dissociation from actin should be reduced,...

Barnacle single muscle fibers were microinjected with the calcium-specific photoprotein aequorin. We have previously shown (Ridgway, E. B., and A. M. Gordon, 1984, Journal of General Physiology, 83:75-104) that when barnacle are stimulated under voltage clamp length control allowed to shorten during declining phase calcium transient, extra myoplasmic is observed. The time course for shortening steps at different times transient intermediate between those free force. Furthermore, amplitude...

Insulin-induced membrane changes were investigated in K(+)-depleted rat muscle. Male Sprague-Dawley rats placed on a K(+)-free but otherwise adequate diet for 5-8 wk; serum K+ concentration ([K+]) dropped to 1.2-3.2 mM. Omohyoid potential was -81 mV 5.5 mM [K+] (SO4(2-)). Exposure either insulin or low (0.5 mM) singly changed only slightly. The combination resulted depolarization of 90% fibers (-43 mV) and hyperpolarization 10% (-101 mV). Fibers from normokalemic did not depolarize....

This study investigated the influence of muscle source and fiber type on calcium sensitivity skinned rat skeletal fibers from predominantly slow muscles [soleus (SOL) adductor longus (AL)], mixed [posterior gracilis (PG)], fast-twitch [extensor digitorum (EDL)]. Fibers were characterized histochemically by one-dimensional protein gel electrophoresis, calcium-tension relationships determined. Fiber had significant effects negative log concentration associated with half-maximal tension...

We explored the possibility that glucocorticoid-induced muscle weakness and atrophy resulted from impaired membrane excitability. Male Sprague-Dawley rats received intramuscular injections of dexamethasone, cortisone acetate (equivalent anti-inflammatory doses), or saline for up to 28 days. Temporal patterns change in mass, twitch tetanic tension, potential, cable parameters, excitability were studied vitro extensor digitorum longus (EDL), soleus (SOL), omohyoid (OMO), caudofemoralis (CF),...

In single muscle fibers from the giant barnacle, a small decrease in length decreases both calcium activation and peak isometric tension produced by constant current stimulus. The effect is most pronounced if change immediately precedes stimulation. some cases, with shortening can be accounted for almost entirely release rather than changes mechanical factors such as filament geometry. During stimulation membrane becomes more depolarized at longer lengths shorter lengths. Under voltage clamp...