The removal of myoplasmic free calcium following calcium release in frog skeletal muscle.

Abstract

SUMMARY1. Transient changes in intracellular free calcium concentration (A[Ca2+]) in response to pulse depolarizations were monitored in isolated segments of single frog skeletal muscle fibres cut at both ends and voltage clamped at a holding potential of -90 mV in a double-Vaseline-gap chamber. Calcium transients were monitored optically using the metallochromic indicator dye Antipyrylazo III (APIII), which entered the fibre by diffusion from the solution applied to the cut ends.2. Optical artifacts due to fibre movement were minimized or eliminated by stretching the fibres to sarcomere lengths at which there was little or no overlap of thick and thin contractile filaments. Remaining movement-independent optical changes intrinsic to the fibre and unrelated to the dye were monitored at 850 nm, where free and dye-bound APIII have no absorbance. These 850 nm signals scaled by A-1 2 were used to remove intrinsic components from the signals at 700 or 720 nm, wave-lengths at which the APIJI absorbance increases when calcium is bound. The corrected 700 or 720 nm signals were used to calculate A[Ca2+].3. The decay of A[Ca2+] following fibre repolarization at the termination of a depolarizing pulse was well described by a single exponential plus a constant. Ca2+] following fibre repolarization after any given pulse became slower with increasing dye concentration. This reflects the rapid calcium-buffering action of APIII and could be used to estimate the rapid calcium-buffering activity intrinsic to the fibre.8. The components of the removal model and the intrinsic rapid calcium buffer are discussed in terms of the biochemical constituents known to be present in skeletal muscle fibres.

Processes that remove calcium from the cytoplasm during excitation‐contraction coupling in intact rat heart cells.

“…In seven experiments, this factor was, on average, 086 + 009 (i +or). We have therefore proceeded with the analysis on the assumption that the values listed in Table 1 (Melzer, Rios & Schneider, 1986 the result of the SR Ca2+ pump, operating far from saturation and as dimeric units. In mammalian cardiac muscle, however, the evidence presented so far is that the SR is the dominant process (Fig.…”

“…- primarily by the relatively slow binding of Ca2" to an 'intermediate sink', the Ca2" ligand parvalbumin (Melzer et al 1986 (Bers, Bridge & MacLeod, 1987 (Wier, 1990;Noble & Powell, 1991), cytoplasmic Ca2+ ligands have a major influence on the time course of the removal of Ca2+ from the cytoplasm. Addition of relatively small amounts of a high-affinity Ca2" ligand (indo-1) influence the declining phase of the [Ca21]i transient profoundly (Fig.…”

Calcium signals recorded from cut frog twitch fibers containing antipyrylazo III.

“…In their experiments, carried out using voltage clamp, antipyrylazo III was continuously present in the end-pool solutions and its concentration inside the fiber always increased with time . They (and also Melzer et al, 1986) analyzed their results in terms of rapidly equilibrating Ca-binding sites intrinsic to the fiber; the progressive slowing of the Ca signal was assumed to be due exclusively to the increase in Ca buffering associated with the increase in indicator concentration . The results in this article show that this assumption is not correct, at least under our experimental conditions .…”

Effects of tetracaine on sarcoplasmic calcium release in mammalian skeletal muscle fibres

“…1, left column) as described by Kov acs et al (1983) using the correction for intrinsic fibre absorbance at 850 nm following the procedure in Melzer et al (1986). Fura_2 fluorescence was used to calculate the resting [Ca¥]é.…”