Kinetics of rapid Ca2+ release by sarcoplasmic reticulum. Effects of Ca2+, Mg2+, and adenine nucleotides

Journal Article · Tue Jan 14 04:00:00 EST 1986 · Biochemistry; (United States)

OSTI ID:5617512

Meissner, G; Darling, E; Eveleth, J

A radioisotope flux-rapid-quench-Millipore filtration method is described for determining the effects of Ca2+, adenine nucleotides, and Mg2+ on the Ca2+ release behaviour of heavy sarcoplasmic reticulum (SR) vesicles. Rapid 45Ca2+ efflux from passively loaded vesicles was blocked by the addition of Mg2+ and ruthenium red. At pH 7 and 10(-9) M Ca2+, vesicles released 45Ca2+ with a low rate (k = 0.1 s-1). An increase in external Ca2+ concentration to 4 microM or the addition of 5 mM ATP or the ATP analogue adenosine 5'-(beta,gamma-methylenetriphosphate) (AMP-PCP) resulted in intermediate 45Ca2+ release rates. The maximal release rate was observed in media containing 4 microM Ca2+ and 5 mM AMP-PCP and had a first-order rate constant of 30-100 s-1. Mg2+ partially inhibited Ca2+- and nucleotide-induced 45Ca2+ efflux. In the absence of AMP-PCP, 45Ca2+ release was fully inhibited at 5 mM Mg2+ or 5 mM Ca2+. The composition of the release media was systematically varied, and the flux data were expressed in the form of Hill equations. The apparent n values of activation of Ca2+ release by ATP and AMP-PCP were 1.6-1.9. The Hill coefficient of Ca2+ activation (n = 0.8-2.1) was dependent on nucleotide and Mg2+ concentrations, whereas the one of Mg2+ inhibition (n = 1.1-1.6) varied with external Ca2+ concentration. These results suggest that heavy SR vesicles contain a Ca2+ release channel which is capable of conducting Ca2+ at rates comparable with those found in intact muscle. Ca2+, AMP-PCP (ATP), and Mg2+ appear to act at noninteracting or interacting sites of the channel.

• Research Organization: Univ. of North Carolina, Chapel Hill
• OSTI ID: 5617512
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 1; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

551001* -- Physiological Systems-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
AMP
ANIMALS
ATP
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM
CALCIUM 45
CALCIUM ISOTOPES
CELL CONSTITUENTS
DAYS LIVING RADIOISOTOPES
ELEMENTS
EVEN-ODD NUCLEI
INHIBITION
INTERMEDIATE MASS NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
MAGNESIUM
MAMMALS
MEMBRANE TRANSPORT
METALS
MUSCLES
NUCLEI
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANOIDS
RABBITS
RADIOISOTOPES
SARCOPLASMIC RETICULUM
TRACER TECHNIQUES
VERTEBRATES