A fluorescence stopped flow analysis of Ca2+ exchange with troponin C.

Johnson, J D; Charlton, S C; Potter, James D.

doi:10.1016/s0021-9258(18)50787-0

Cited by 182 publications

(24 citation statements)

References 17 publications

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“…What is the rate-limiting process within thin filament activation regulates k tr during submaximal Ca 2ϩ activations? Because the rate of Ca 2ϩ binding to N-terminal sites of both skeletal and cardiac muscle TnC appears to be diffusion-limited (or very nearly so) (Johnson et al, 1979(Johnson et al, , 1980(Johnson et al, , 1994Rosenfeld and Taylor, 1985), another step in the thin filament activation process is probably rate-limiting. This could be the rate of Ca 2ϩ dissociation from TnC, a Ca 2ϩ -dependent conformational transition within TnC, or a Ca 2ϩ -dependent interaction between TnC and another thin filament regulatory protein (TnI, TnT).…”

Section: Discussionmentioning

confidence: 99%

Regulation of Skeletal Muscle Tension Redevelopment by Troponin C Constructs with Different Ca2+ Affinities

Regnier

Rivera

Chase

et al. 1999

Biophysical Journal

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In maximally activated skinned fibers, the rate of tension redevelopment (ktr) following a rapid release and restretch is determined by the maximal rate of cross-bridge cycling. During submaximal Ca2+ activations, however, ktr regulation varies with thin filament dynamics. Thus, decreasing the rate of Ca2+ dissociation from TnC produces a higher ktr value at a given tension level (P), especially in the [Ca2+] range that yields less than 50% of maximal tension (Po). In this study, native rabbit TnC was replaced with chicken recombinant TnC, either wild-type (rTnC) or mutant (NHdel), with decreased Ca2+ affinity and an increased Ca2+ dissociation rate (koff). Despite marked differences in Ca2+ sensitivity (>0.5 DeltapCa50), fibers reconstituted with either of the recombinant proteins exhibited similar ktr versus tension profiles, with ktr low (1-2 s-1) and constant up to approximately 50% Po, then rising sharply to a maximum (16 +/- 0.8 s-1) in fully activated fibers. This behavior is predicted by a four-state model based on coupling between cross-bridge cycling and thin filament regulation, where Ca2+ directly affects only individual thin filament regulatory units. These data and model simulations confirm that the range of ktr values obtained with varying Ca2+ can be regulated by a rate-limiting thin filament process.

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Section: Discussionmentioning

confidence: 99%

Regulation of Skeletal Muscle Tension Redevelopment by Troponin C Constructs with Different Ca2+ Affinities

Regnier

Rivera

Chase

et al. 1999

Biophysical Journal

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“…Based upon studies of divalent cation binding to troponin, Potter and co-workers (Potter and Gergely, 1975 ;Johnson et al, 1979) have identified the low-affinity, Cat'-specific binding sites on troponin C (TnC) as the putative sites that regulate contraction. Potter and Gergely (1975) obtained a good fit of their model with the relation between myofibrillar ATPase and Ca2+ by assuming that ATPase is directly proportional to the occupancy of the Ca2+specific sites on troponin by Ca 21 .…”

Section: Discussionmentioning

confidence: 99%

Influence of temperature upon contractile activation and isometric force production in mechanically skinned muscle fibers of the frog.

Godt¹,

Lindley²

1982

The Journal of General Physiology

436

290

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Increasing temperature (4-22°C) increases the Ca 21 concentration required for activation of mechanically skinned frog muscle fibers . The pCa required for 50% maximal force (pCa5o) was inversely proportional to absolute temperature. Assuming that relative force is directly related to fractional occupancy of the C2-binding sites on troponin that regulate force, the shift was consistent with a Gibbs free energy change of binding (AG) of about -7 .8 kcal/ mol. This is close to the AG for Ca 2+ binding to the calcium-specific sites on troponin C reported by others . Decreasing Mgt' from 1 mM to 60 NAM shifts the force-pCa curves at either 4 or 22°C to higher pCa, but the shift of pCaso with temperature over this range (0 .4 log units) was the same at low and high Mg t+ . Maximal force increased with temperature for the entire range 4-22°C with a Q,jo of 1 .41, and over the restricted range 4-15°C with a Quo of 1 .20. From the dual effects of temperature on Cat+ activation and maximal force, one would expect that force would respond differently to temperature change at high or low Cat+ . At high Cat+ , a temperature increase will lead to an increased force. However, at low to intermediate Ca 2+ levels (below the intersection of the forcepCa curves for the initial and final temperatures), steady state force should decrease with increasing temperature. The inverse responses should occur with a decrease in temperature. These responses are observed when temperature is changed by rapid solution exchange.

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“…The consistent finding is that the free calcium concentration increases in muscle before the force rises and declines before the force falls. Using measure-THE JOURNAL OF GENERAL PHYSIOLOGY -VOLUME 83 -1984 ments of the rate constants for calcium association and dissociation from troponin (Johnson et al ., 1979), Robertson et al . (1981) have proposed models predicting the time course of changes in bound calcium levels during activation, but no direct measurements have been made in intact muscle fibers.…”

Section: Introductionmentioning

confidence: 99%

Muscle calcium transient. Effect of post-stimulus length changes in single fibers.

Ridgway¹,

Gordon²

1984

The Journal of General Physiology

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We examined the effects of post-stimulus length changes on voltage-clamped, aequorin-injected single muscle fibers from the barnacle Balanus nubilus. Extra light (extra calcium) is seen when the fiber is allowed to shorten (a small percentage) during the declining phase of the calcium transient. The opposite is observed when the fiber is stretched. Increasing the extent of shortening increases the amount of extra calcium, as does decreasing the temperature. The extra calcium probably comes from the myofilaments and not from the sarcoplasmic reticulum because (a) there is a strong correlation between the extra calcium and the level of activation ; (b) there is a strong correlation between the extra calcium and the amount of force redeveloped after a length change ; and (c) the time course of the appearance of the extra calcium is intermediate between that of the free calcium concentration and that of force. We suggest (a) that the calcium binding to the activating myofibrillar proteins is sensitive to muscle length or muscle force, and (b) that there is a pool of bound calcium (activating calcium) that waxes and wanes with a time course intermediate between the free calcium concentration and force.

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A fluorescence stopped flow analysis of Ca2+ exchange with troponin C.

Cited by 182 publications

References 17 publications

Regulation of Skeletal Muscle Tension Redevelopment by Troponin C Constructs with Different Ca2+ Affinities

Regulation of Skeletal Muscle Tension Redevelopment by Troponin C Constructs with Different Ca2+ Affinities

Influence of temperature upon contractile activation and isometric force production in mechanically skinned muscle fibers of the frog.

Muscle calcium transient. Effect of post-stimulus length changes in single fibers.

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