Inositol 1,4,5-trisphosphate increases myoplasmic [Ca2+] in isolated muscle fibers. Depolarization enhances its effects

J. R. Lopez, L. Parra

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Inositol 1,4,5-trisphosphate (InsP3) has been proposed as an intracellular messenger which mobilizes calcium from the sarcoplasmic reticulum, during excitation-contraction coupling in skeletal muscle. We have measured the myoplasmic free calcium concentration ([Ca2+]i) by means of calcium selective microelectrodes in intact fibers isolated from Leptodactylus insularis microinjected with InsP3. In muscle fibers bathed in normal Ringer, the mean resting [Ca2+]i was 0.11 ± 0.01 μM (M ± SEM, n = 30). The microinjection of 0.3, 0.5 and 1 μM InsP3 induced transient increments in the [Ca2+]i to 0.35 ± 0.02 μM (n = 9), to 0.53 ± 0.03 μM (n = 11) and 0.94 ± 0.06 μM (n = 10) respectively. Microinjection of 0.3, 0.5 and 1 μM InsP3 in muscle fibers incubated in low Ca2+ solution induced increments in [Ca2+]i similar to those observed in fibers bathed with normal Ringer. The microinjection of 0.3, 0.5 and 1 μM InsP3 in muscle fibers partially depolarized with 10 mM [K+]o induced transient enhancements of the resting [Ca2+]i that were greater than the transients observed in the normally polarized muscle. In partially depolarized fibers microinjected with 0.3, 0.5 and 1 μM InsP3, the [Ca2+]i was changed to 1.45 ± 0.14 μM (n = 20), to 3.37 ± 0.34 μM (n = 7) and to 7.43 ± 0.70 μM (n = 6) respectively. In all partially depolarized fibers these increments in [Ca2+]i were associated with local contraction. These data support the hypothesis that InsP3 could play an important role as an intracellular messenger involved in the calcium release process in skeletal muscle, and that the InsP3 effect on Ca2+ release might be regulated by the membrane potential.

Original languageEnglish (US)
Pages (from-to)543-557
Number of pages15
JournalCell Calcium
Volume12
Issue number8
DOIs
StatePublished - 1991
Externally publishedYes

ASJC Scopus subject areas

  • Physiology
  • Molecular Biology
  • Cell Biology

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