title: Temperature affects human cardiac sarcoplasmic reticulum energy-mediated calcium transport.
abstract: Hypothermic cardioplegic solutions are currently used to preserve cardiac function during transportation. However, it has been shown that end-diastolic compliance decreases in donor hearts during reperfusion. Excessively cold temperatures may affect membrane-bound enzymes (Ca2+ ATPase and Ca2+ uptake) which are necessary for calcium homeostasis. To study the effect of temperature on Ca2+ ATPase and Ca2+ uptake activities over the temperature range to which a donor heart is usually exposed (4 degrees-37 degrees C), sarcoplasmic reticulum (SR) was isolated from human atrial appendages. SR was also isolated from atrial appendages which had been stored in saline at 4 degrees C for 4 or 24 h or 24 h in St Thomas' cardioplegic solution (ST). Ca2+ ATPase and Ca2+ uptake from these samples were compared with those found in the SR of unstored appendages. The activity of Ca2+ uptake and Ca2+ ATPase showed great sensitivity at assay temperatures below 22 degrees C, while no such sensitivity was identified in SR NADPH/cytochrome C reductase (NCR). After storage of atrial appendages for only 4 h in saline at 4 degrees C, Ca2+ uptake activity was reduced 50% in the SR when compared to unstored controls (80 +/- 9.9 nmol/mg/min and 155.24 +/- 2.4 nmol/mg/min, respectively; P < 0.02) whereas Ca2+ ATPase was not affected until 24 h of storage, when the activity was also decreased > 50% (P = 0.0002). However, NCR was not affected. In addition, storage at 4 degrees C significantly decreased the SR protein yield (mg/g homogenate protein) at 4 or 24 h in saline as well as 24 h in ST. However, there was no decrease in the enzyme activities (Ca2+ ATPase, 229 +/- 25.3; Ca2+ uptake, 221 +/- 27.1; NCR, 24.9 +/- 0.48 nmol/mg/min). Following exposure to low temperature, alteration of Ca2+ uptake and Ca2+ ATPase may result in disruption of calcium homeostasis, thereby interrupting excitation-contraction coupling and relaxation. The damaging effects of hypothermia should be taken into account when assessing the peri-operative complications and the long-term results of cardiac transplantation.
authors.affiliation: Cardiovascular Devices Division, University of Ottawa Heart Institute, Ottawa Civic Hospital, Ontario, Canada.
authors.forename: R S
authors.initials: RS
authors.lastname: Labow
authors.forename: P J
authors.initials: PJ
authors.lastname: Hendry
authors.forename: E
authors.initials: E
authors.lastname: Meek
authors.forename: W J
authors.initials: WJ
authors.lastname: Keon
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003080:Cold Temperature; D006325:Heart Atria; D006801:Humans; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009926:Organ Preservation; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D009251:NADPH-Ferrihemoprotein Reductase; D000252:Calcium-Transporting ATPases; D002118:Calcium