Mechanisms of fatty acid effects on sarcoplasmic reticulum. III. The effects of palmitic and oleic acids on sarcoplasmic reticulum function–a model for fatty acid membrane interactions.

F C Messineo,M Rathier,C Favreau,J Watras,H Takenaka

doi:10.1016/s0021-9258(17)43607-6

Abstract

The mechanism by which palmitic and oleic acids modify calcium sequestration by sarcoplasmic reticulum vesicles was investigated by examining the effects of these fatty acids on calcium-dependent ATPase activity, on the phosphoenzyme intermediates found during calcium sequestration reactions, and on passive membrane permeability to calcium. The calcium sequestered in the presence of these fatty acids was also characterized by determining the amount exchangeable with the extravesicular pool or released by the ionophore A23187. In the presence of 50 microM ATP, 18 microM palmitic acid enhanced and 18 microM oleic acid inhibited calcium sequestration, whereas both fatty acids stimulated ATPase activity. Neither fatty acid had significant effects on the amount or distribution of the phosphoenzyme formed during the calcium transport reaction. Palmitic acid stimulated calcium sequestration only when ATP was present. Oleic acid caused the release of a portion of the accumulated calcium during ATP-supported calcium sequestration and also enhanced the release observed in ATP-depleted reactions. A portion of the calcium sequestered in the presence of palmitic acid appears to be incorporated into a nonexchangeable and ionophore-insensitive calcium pool, although the latter was estimated to be considerably larger than the nonexchangeable pool. These data support the hypothesis that oleic acid inhibits calcium sequestration by increasing membrane permeability to calcium, whereas palmitic acid appears to stimulate calcium sequestration by interacting with a portion of the calcium within the vesicles to form a separate, poorly exchangeable calcium pool.

Highlights

The mechanism by which palmitic and oleic acids phorylated, enzyme intermediate EIP
ATPase activity as both fatty acids stimulated steady state had been inhibited by A23187
ATPase activity to a similar degree at concentrations that these low concentrations of palmitic acid do not interact at have opposite effects on calcium sequestration (Fig. 2)

Summary

RESULTS

Without effect and oleic acidslightly inhibited calciumsequestration, both fatty acids stimulated ATPase activity by more than 75% (Fig. 2). Reactions carried out at high concentrations of ATP (Fig. 1). I CONTROL c4 theseexperiments,palmitic acid hadno effect on calcium association with the sarcoplasmic reticulum [17]. Effects of Palmitic andOleic Acids on ATPase Activity-At concentrations (6-24 p ~ th)at hadopposite effectson calcium. *oleic acids, ATPase activity increased to 2.12 f 0.23 and 1.81 0.14 pmol/mg.min, respectively. Effect of palmitic and oleic acids on the ATPase activity,E 2 P amount, and theE2Pdecay rate constant. Reactions were carried out in 10 pM added calcium, with 12 pg/ml ofprotein and initiatedwith 50 IJMMg[y-:’2P]ATP.The basal ATPase under these conditions is approximately 20-40 nmol of P;/mg.min and was disregarded in the above calculations. The ATPase activity is the mean c S.E. for 4 experiments

18 U M oleic acid

E P EIP EeP

Findings

DISCUSSION