Combined effects of age and dietary fat on β₁-receptors and Ca²⁺ channels in rat hearts

Male Wistar rats were fed a standard diet or diets supplemented with 10% butter, 10% corn oil, or 10% cod liver oil from the age of 2 mo. At 7 and 24 mo of age, the fatty acid composition of total phospholipids was determined in ventricular crude sarcolemma preparations; binding capacity and affinity (1/K(d)) of [³H]dihydroalprenolol and [³H]nitrendipine binding were also determined. The arachidonic acid level was significantly higher at 24 mo than at 7 mo of age in the membrane phospholipids in rats fed no extra fat, but in rats fed fat-supplemented diets, age had no effect. Affinity of Ca²⁺ channels for [³H]nitrendipine decreased significantly in all dietary groups between 7 and 24 mo of age, whereas the affinity of β₁-receptors for [³H]dihydroalprenolol increased in corn oil-fed rats. Density of β₁-receptors decreased significantly in corn oil- and butter-fed rats and rats fed no extra fat between 7 and 24 mo of age, whereas the density of Ca²⁺ channels decreased significantly in corn oil-fed rats. We conclude that the antagonist binding properties of Ca²⁺ channels and β₁-adrenergic receptors in rat hearts may change with age depending on the dietary fat.