title: Effects of hypocaloric feeding and refeeding on myocardial Ca and ATP cycling in the rat.
abstract: Hypocaloric feeding (HCF) depresses heart function causing cardiac atrophy, bradycardia, and decreased cardiac output. We tested the hypothesis that HCF results in decreased myocardial Ca- and ATP cycling. We reduced protein-calorie intake of adult rats by 20% for 7 days and then allowed them to recover for 3 days. Changes in ionized Ca concentration (nM/s) of 2.5% myocardial homogenates that were attributable to the Ca-ATPase pump and Ca-release channel (CRC), respectively, of the sarcoplasmic reticulum (SR) were depressed 41 and 85% by HCF from 61.6 +/- 9.4 and 24.7 +/- 3.3, to 36.1 +/- 2.8 and 3.6 +/- 2.9. Activity of the Ca-pump was restored after 3 days of refeeding, whereas the CRC remained 23% depressed (all p < 0.05). Additionally, the CRC activity was inhibited to a 3-fold greater extent than controls by HCF, but was disinhibited within one day of refeeding. The greater effect on CRC than Ca-pump activity resulted in net Ca-uptake being unaffected by HCF. In addition to depression of Ca-cycling, ATP sythetase and total ATPase activities (IU/g), respectively, were depressed 20 and 15% by HCF from 174 +/- 19 and 51.3 +/- 3.8 to 140 +/- 15 and 43.7 +/- 4.7, but were restored to control values within one day of refeeding. We conclude that HCF produces a compensatory, reversible, and asymmetric downregulation and inhibition of Ca-cycling, with the CRC being preferentially affected.
authors.affiliation: Department of Pathology, Ontario Veterinary College, University of Guelph, Canada.
authors.forename: P J
authors.initials: PJ
authors.lastname: O'Brien
authors.forename: H
authors.initials: H
authors.lastname: Shen
authors.forename: D
authors.initials: D
authors.lastname: Bissonette
authors.forename: K N
authors.initials: KN
authors.lastname: Jeejeebhoy
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001835:Body Weight; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D003402:Creatine Kinase / Q000378:metabolism; D015536:Down-Regulation; D002149:Energy Intake; D005508:Food Deprivation / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism; D009929:Organ Size; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D009211:Myoglobin; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D003402:Creatine Kinase; D006180:Proton-Translocating ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium