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.
Gilchrist
James S C
JS
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
Palahniuk
Chris
C
Abrenica
Bernard
B
Rampersad
Penelope
P
Mutawe
Mark
M
Cook
Tom
T
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