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Effects of intracellular pH and [Mg2+] on excitation‐contraction coupling in skeletal muscle fibres of the rat.
Author(s) -
Lamb G D,
Stephenson D G
Publication year - 1994
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.1994.sp020253
Subject(s) - depolarization , biophysics , chemistry , contraction (grammar) , intracellular , extensor digitorum longus muscle , skeletal muscle , endoplasmic reticulum , muscle contraction , calcium , anatomy , biochemistry , endocrinology , biology , organic chemistry
1. The effects on normal excitation‐contraction (E‐C) coupling of two important intracellular ions, H+ and Mg2+, were examined in skinned fibres from the extensor digitorum longus muscle of rat. 2. A single depolarization (2‐3 s duration) in the presence of 1 mM Mg2+ (pH 7.1, 23 degrees C) released most of the available Ca2+ in the sarcoplasmic reticulum (SR), but a similar depolarization in the presence of 10 mM Mg2+ was unable to release almost any Ca2+. Thus, raised [Mg2+] potently inhibits depolarization‐induced Ca2+ release in mammalian muscle. 3. Depolarization at pH 6.2 (1 mM Mg2+, 23 degrees C) induced a large force response, which was on average 78 +/‐ 2%, n = 6, of the depolarization‐induced response at pH 7.1; this reduction resulted from a corresponding reduction in maximum Ca(2+)‐activated force at pH 6.2. Similar results were obtained at 37 degrees C. Also, a single depolarization at pH 6.2 caused almost complete depletion of the releasable Ca2+ in the SR. Thus, low pH does not prevent depolarization‐induced Ca2+ release in mammalian muscle. 4. Lowering the free [Mg2+] from 1 mM to 15 microM caused massive release of Ca2+, and depletion of the SR, at both pH 7.1 and 6.2, indicating that over this pH range, H+ did not readily substitute for Mg2+ at its inhibitory site on the Ca2+ release channel.(ABSTRACT TRUNCATED AT 250 WORDS)