Effects of creatine phosphate and P(i) on Ca2+ movements and tension development in rat skinned skeletal muscle fibres.

Abstract

1. Mechanically skinned fast-twitch (FT) and slow-twitch (ST) muscle fibres of the rat were used to investigate the effects of fatigue-like changes in creatine phosphate (CP) and inorganic phosphate (Pi) concentration on Ca2+-activation properties of the myofilaments as well as Ca2+ movements into and out of the sarcoplasmic reticulum (SR). 2. Decreasing CP from 50 mm to zero in FT fibres increased maximum Ca2+-activated tension (Tmax) by 16 + 2 % and shifted the mid-point of the tension-pCa relation (pCa50) to the left by 0'28 + 0 03 pCa units. In ST fibres, a decrease of CP from 25 mm to zero increased Tmax by 9 + 1 % and increased the pCa50 by 0 16 + 0 01 pCa units. The effect of CP on Tmax was suppressed in both fibre types by prior treatment with 0 3 mm FDNB (1-fluoro-2,4-dinitrobenzene), suggesting that these effects may occur via changes in creatine kinase activity. 3. Increases of Pi in the range 0-50 mm reduced the pCa50 and Tmax in both fibre types.These effects were more pronounced in ST fibres than in FT fibres in absolute terms. However, normalization of the results to resting Pi levels appropriate to both fibre types (1 mm for FT and 5 mm for ST fibres) revealed similar decreases in Tmax (% 39% at 25 mM Pi and -48% at 50 mm Pi) and pCa50 (0 25

Mitochondrial free [Ca2+] levels and the permeability transition

“…Increasing the phosphate content of the medium had an effect on [Ca 2+ ] M increase or Ca 2+ release from mitochondria only when it reached the near-millimolar range, as expected from the solubility of the CaHPO 4 complex in ionic solutions or in other cellular compartments such as the endoplasmic reticulum (16). Our data strongly contrast with those obtained with fluorescent dyes such as fura2-FF in purified mitochondrial preparations [6,7], which showed much lower maximum free [Ca 2+ ] values (below 5 M) in the mitochondrial matrix.…”

Sodium phosphate enhances plasmid DNA expression in vivo

“…[27][28][29][30][31] Phosphate ion applied intracellularly or extracellularly to myofiber cells enters the sarcoplasmic reticulum and precipitates calcium, which in turn decreases muscle contraction. 32,33 Thus, sodium phosphate injections into muscle could somehow aid the entry of plasmid DNA into muscle cells. It has been reported that calcium is required for cell membrane resealing by a process involving recruitment of intracellular membrane vesicles which bind to, fuse with and patch damaged plasmalemma.…”

El acoplamiento excitación-contracción en el músculo esquelético: preguntas por responder a pesar de 50 años de estudio

“…También se ha encontrado aumento del fosfato (P i ) libre durante el desarrollo de la fatiga y esto parece favorecer el depósito de Ca 2+ dentro del retículo sarcoplásmico en la forma de fosfato de Ca 2+ , lo cual disminuye el Ca 2+ disponible para ser liberado (115,116). Además, el aumento de P i causa disminución de la sensibilidad del mecanismo contráctil al Ca 2+ para generar tensión (86,100).…”