RyR1/SERCA1 cross-talk regulation of calcium transport in heavy sarcoplasmic reticulum vesicles.
We investigated the functional interdependence of sarco-endoplasmic reticulum Ca2+ ATPase isoform 1 and ryanodine receptor isoform 1 in heavy sarcoplasmic reticulum membranes by synchronous fluorescence determination of extravesicular Ca2+ transients and catalytic activity. Under conditions of dynamic Ca2+ exchange ATPase catalytic activity was well coordinated to ryanodine receptor activation/inactivation states. Ryanodine-induced activation of Ca2+ release channel leaks also produced marked ATPase activation in the absence of measurable increases in bulk free extravesicular Ca2+. This suggested that Ca2+ pumps are highly sensitive to Ca2+ release channel leak status and potently buffer Ca2+ ions exiting cytoplasmic openings of ryanodine receptors. Conversely, ryanodine receptor activation was dependent on Ca2+-ATPase pump activity. Ryanodine receptor activation by cytosolic Ca2+ was (i) inversely proportional to luminal Ca2+ load and (ii) dependent upon the rate of presentation of cytosolic Ca2+. Progressive Ca2+ filling coincided with progressive loss of Ca2+ sequestration rates and at a threshold loading, ryanodine-induced Ca2+ release produced small transient reversals of catalytic activity. These data indicate that attainment of threshold luminal Ca2+ loads coordinates sensitization of Ca2+ release channels with autogenic inhibition of Ca2+ pumping. This suggests that Ca2+-dependent control of Ca2+ release in intact heavy sarcoplasmic reticulum membranes involves a Ca2+-mediated "cross-talk" between sarco-endoplasmic reticulum Ca2+ ATPase isoform 1 and ryanodine receptor isoform 1.
Department of Oral Biology, Division of Stroke and Vascular Disease, St. Boniface General Hospital Research Centre, Room 4024, 351 Taché Avenue, University of Manitoba, Winnipeg, MB R2H 2A6, Canada. James_Gilchrist@sbrc.ca
James S C
JS
Gilchrist
Chris
C
Palahniuk
Bernard
B
Abrenica
Penelope
P
Rampersad
Mark
M
Mutawe
Tom
T
Cook
D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002384:Catalysis; D004591:Electrophoresis, Polyacrylamide Gel; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013997:Time Factors
D015220:Calcium Channels; D005456:Fluorescent Dyes; D020033:Protein Isoforms; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium