Abstract
Changes in [Mg2+] in a millimolar range have a significant inverse effect on the Ca2+ (or Sr2+) activated tension generation of skeletal muscle fibers. Single frog (Rana pipiens) semitendinosus muscle fibers were 'skinned' (sarcolemma removed) and contracted isometrically in bathing solutions of varying [Ca2+] or [Sr2+] and [Mg2+] but at constant pH, [MgATP2-], [K+], [CP2-], [CPK], and ionic strength. Ca2+ (or Sr2+) activated steady state tensions were recorded for three [Mg2+]'s: 5x10-5 M, 1 x 10-3 M, and 2x10-3 M; and these tensions were expressed as the percentages of maximum tension generation of the fibers for the same [Mg2+]. Maximum tension was not affected by [Mg2+] within Ca2+ activating or Sr2+ activating sets of solutions; however, the submaximum Ca2+ (or Sr2+) activated tension is strongly affected in an inverse fashion by increasing [Mg2+]. Mg2+ behaves as a competitive inhibitor of Ca2+ and also affects the degree of cooperativity in the system. At [Mg2+] = 5x10-5 M the shape of tension versus [Ca2+] (or [Sr2+]) curve showed evidence of cooperativity of Ca2+ (or Sr2+) binding or activation of the contractile system. As [Mg2+] increased, the apparent affinity for Ca2+ or Sr2+ and cooperativity of the contractile system declined. The effect on cooperativity suggests that as [Mg2+] decreases a threshold for Ca2+ activation appears.
| Original language | English |
|---|---|
| Pages (from-to) | 427-444 |
| Number of pages | 18 |
| Journal | Journal of General Physiology |
| Volume | 66 |
| Issue number | 4 |
| State | Published - Dec 1 1975 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Physiology
Cite this
Characterization of the effects of Mg2+ on Ca2+ and Sr2+ activated tension generation of skinned skeletal muscle fibers. / Donaldson, S. K B; Kerrick, W. Glenn.
In: Journal of General Physiology, Vol. 66, No. 4, 01.12.1975, p. 427-444.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Characterization of the effects of Mg2+ on Ca2+ and Sr2+ activated tension generation of skinned skeletal muscle fibers
AU - Donaldson, S. K B
AU - Kerrick, W. Glenn
PY - 1975/12/1
Y1 - 1975/12/1
N2 - Changes in [Mg2+] in a millimolar range have a significant inverse effect on the Ca2+ (or Sr2+) activated tension generation of skeletal muscle fibers. Single frog (Rana pipiens) semitendinosus muscle fibers were 'skinned' (sarcolemma removed) and contracted isometrically in bathing solutions of varying [Ca2+] or [Sr2+] and [Mg2+] but at constant pH, [MgATP2-], [K+], [CP2-], [CPK], and ionic strength. Ca2+ (or Sr2+) activated steady state tensions were recorded for three [Mg2+]'s: 5x10-5 M, 1 x 10-3 M, and 2x10-3 M; and these tensions were expressed as the percentages of maximum tension generation of the fibers for the same [Mg2+]. Maximum tension was not affected by [Mg2+] within Ca2+ activating or Sr2+ activating sets of solutions; however, the submaximum Ca2+ (or Sr2+) activated tension is strongly affected in an inverse fashion by increasing [Mg2+]. Mg2+ behaves as a competitive inhibitor of Ca2+ and also affects the degree of cooperativity in the system. At [Mg2+] = 5x10-5 M the shape of tension versus [Ca2+] (or [Sr2+]) curve showed evidence of cooperativity of Ca2+ (or Sr2+) binding or activation of the contractile system. As [Mg2+] increased, the apparent affinity for Ca2+ or Sr2+ and cooperativity of the contractile system declined. The effect on cooperativity suggests that as [Mg2+] decreases a threshold for Ca2+ activation appears.
AB - Changes in [Mg2+] in a millimolar range have a significant inverse effect on the Ca2+ (or Sr2+) activated tension generation of skeletal muscle fibers. Single frog (Rana pipiens) semitendinosus muscle fibers were 'skinned' (sarcolemma removed) and contracted isometrically in bathing solutions of varying [Ca2+] or [Sr2+] and [Mg2+] but at constant pH, [MgATP2-], [K+], [CP2-], [CPK], and ionic strength. Ca2+ (or Sr2+) activated steady state tensions were recorded for three [Mg2+]'s: 5x10-5 M, 1 x 10-3 M, and 2x10-3 M; and these tensions were expressed as the percentages of maximum tension generation of the fibers for the same [Mg2+]. Maximum tension was not affected by [Mg2+] within Ca2+ activating or Sr2+ activating sets of solutions; however, the submaximum Ca2+ (or Sr2+) activated tension is strongly affected in an inverse fashion by increasing [Mg2+]. Mg2+ behaves as a competitive inhibitor of Ca2+ and also affects the degree of cooperativity in the system. At [Mg2+] = 5x10-5 M the shape of tension versus [Ca2+] (or [Sr2+]) curve showed evidence of cooperativity of Ca2+ (or Sr2+) binding or activation of the contractile system. As [Mg2+] increased, the apparent affinity for Ca2+ or Sr2+ and cooperativity of the contractile system declined. The effect on cooperativity suggests that as [Mg2+] decreases a threshold for Ca2+ activation appears.
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M3 - Article
C2 - 1081122
AN - SCOPUS:0016589363
VL - 66
SP - 427
EP - 444
JO - Journal of General Physiology
JF - Journal of General Physiology
SN - 0022-1295
IS - 4
ER -