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Decline of myoplasmic Ca2+, recovery of calcium release and sarcoplasmic Ca2+ pump properties in frog skeletal muscle.
Author(s) -
Klein M G,
Kovacs L,
Simon B J,
Schneider M F
Publication year - 1991
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1991.sp018771
Subject(s) - calcium , depolarization , chemistry , endoplasmic reticulum , time constant , biophysics , grenouille , parvalbumin , analytical chemistry (journal) , biology , salientia , biochemistry , chromatography , neuroscience , xenopus , organic chemistry , engineering , gene , electrical engineering
1. The two calcium indicators Antipyrylazo III (AP III) and Fura‐2 were used simultaneously to monitor free myoplasmic [Ca2+] in voltage‐clamped cut segments of frog skeletal muscle fibres (8‐10 degrees C). Antipyrylazo III was used for the relatively large [Ca2+] transients during 100‐200 ms depolarizing pulses to ‐20 to 0 mV and for the rapid decline of [Ca2+] during the 200 ms after the pulses. Fura‐2 was used to follow the slow decline of the small remaining elevation of [Ca2+] during the following 16 s (slow recovery period) and to monitor resting [Ca2+]. 2. From 1 to 16 s of the slow recovery period [Ca2+] declined with two exponential components, having time constants of 1.9 +/‐ 0.3 and 13.5 +/‐ 1.5 s (these and all other values are means +/‐ S.E.M. of eleven runs from seven fibres). At 1.2 s after the end of the pulses the amplitudes of the fast and slow exponential components of decline of [Ca2+] were 34 +/‐ 7 and 31 +/‐ 4 nM, respectively. The resting [Ca2+] in these runs was 40 +/‐ 4 nM. 3. The time course of calcium bound to parvalbumin [( Ca‐Parv]) was calculated from the [Ca2+] records using literature values for the parvalbumin kinetic constants. From 1 to 16 s of the slow recovery period the total calcium [Ca]T outside the sarcoplasmic reticulum (SR) was assumed to equal [Ca‐Parv] + [Ca‐Fura]. During this period [Ca]T declined with two exponential components having time constants of 1.7 +/‐ 0.2 and 14.2 +/‐ 1.4 s, the same as those for [Ca2+]. Assuming the total concentration of parvalbumin cation binding sites to be 1000 microM, the fast and slow components of [Ca]T had amplitudes of 117 +/‐ 21 and 147 +/‐ 16 microM, respectively, at 1.2 s after the pulses. 4. The rate of decline of [Ca]T, ‐d[Ca]T/dt, was used as a measure of the net rate of removal of calcium from the myoplasm by the SR. From 3 to 16 s of the slow recovery period and in the resting fibre ‐d[Ca]T/dt varied with [Ca2+] according to A[Ca2+]n‐L. The term A[Ca2+]n represents the pump rate and L represents a constant rate of calcium leak from the SR. 5. For 40 nM less than or equal to [Ca2+] less than or equal to 80 nM, the power n for the [Ca2+] dependence of pump rate was 3.9 +/‐ 0.6.(ABSTRACT TRUNCATED AT 400 WORDS)