Role of sarcoplasmic reticulum and mitochondria in Ca2+ removal in airway myocytes.
The aim of this study was to use both a theoretical and experimental approach to determine the influence of the sarco-endoplasmic Ca2+-ATPase (SERCA) activity and mitochondria Ca2+ uptake on Ca2+ homeostasis in airway myocytes. Experimental studies were performed on myocytes freshly isolated from rat trachea. [Ca2+]i was measured by microspectrofluorimetry using indo-1. Stimulation by caffeine for 30 s induced a concentration-graded response characterized by a transient peak followed by a progressive decay to a plateau phase. The decay phase was accelerated for 1-s stimulation, indicating ryanodine receptor closure. In Na2+-Ca2+-free medium containing 0.5 mM La3+, the [Ca2+]i response pattern was not modified, indicating no involvement of transplasmalemmal Ca2+ fluxes. The mathematical model describing the mechanism of Ca2+ handling upon RyR stimulation predicts that after Ca2+ release from the sarcoplasmic reticulum, the Ca2+ is first sequestrated by cytosolic proteins and mitochondria, and pumped back into the sarcoplasmic reticulum after a time delay. Experimentally, we showed that the [Ca2+]i decay after Ca2+ increase was not altered by the SERCA inhibitor cyclopiazonic acid, but was slightly but significantly modified by the mitochondria uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. The experimental and theoretical results indicate that, although Ca2+ pumping back by SERCA is active, it is not primarily involved in [Ca2+]i decrease that is due, in part, to mitochondrial Ca2+ uptake.
Roux
Etienne
E
Laboratoire de Physiologie Cellulaire Respiratoire, Institut National de la Santé et de Recherche Médicale E 356, Université Victor Segalen Bordeaux 2, 33076 Bordeaux, France. etienne.roux@u-bordeaux2.fr
Marhl
Marko
M
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002478:Cells, Cultured; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D008962:Models, Theoretical; D032342:Muscle Cells / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013223:Statistics as Topic; D014132:Trachea / Q000378:metabolism
D002110:Caffeine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium