Portland State University. Environmental Sciences and Resources Ph. D. Program
Jonathan J. Abramson
Date of Publication
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Science and Management
Sarcoplasmic reticulum, Calcium in the body
1 online resource (3, x, 132 pages)
Skeletal muscle contains an internal membrane system called the sarcoplasmic reticulum (SR) whose function is to regulate the Ca2+ concentration of the myoplasm. Ca2+ is transported into the SR from the myoplasm via a Ca2+ dependent ATPase thus lowering the myoplasmic Ca2+ concentration. Ca2+ exits from the SR via a Ca2+ releqse pathway resultingin the increase of myoplasmic Ca2+. Muscles contract when the myoplasmic Ca2+ concentration is > 5 uM and relax when the Ca2+ concentration is lowered below 1 uM. The Ca2+ dependent ATPase has been extensively studied but the Ca2+ release system is less well understood.
SR vesicles release their internal Ca2+ when a reactive thiol group is oxidized (oxidation-induced Ca2+ release). It is shown in this dissertation that oxidation-induced Ca2+ release is stimulated by adenine nucleotides with an order of effectiveness of: ATP > AMP-PCP > cAMP > AMP > adenine. The stimulatory effect is not dependent upon phosphorylation of a protein because AMP-PCP, a nonhydrolyzable analogue of ATP, is almost as effective as ATP in stimulating oxidation-induced Ca2+ release.
It is also shown in this dissertation that photooxidation of histidyl residues results in an increase Ca2+ permeability of the SR. Unlike oxidation-induced Ca2+ release, photooxidation-induced Ca2+ release is Mg2+ independent, not inhibited by ruthenium red and inhibited by adenine nucleotides. Covalent modification of histidyl residues with ethoxyformic anhydride results in the increased permeability of SR vesicles. Similar to photooxidation-induced Ca2+ efflux, EFA-induced Ca2+ efflux is Mg2+ independent and is inhibited by ATP. The AMP-PCP protection of SR proteins from modification with EFA is similar to non-competitive inhibition with a KI = 50 uM. The photooxidation effect is not on membrane lipids but on a protein component which may be an ion transport system, other than the Ca2+ release protein, altered in such a way that it now transports Ca2+.
Stuart, Janice F., "Chemical Modification of Skeletal Muscle Sarcoplasmic Reticulum Vesicles: A Study of Calcium Permeability" (1989). Dissertations and Theses. Paper 1389.