Effects of dietary fish oil on calcium homeostasis in rat platelets

Mechanisms to explain the differential effects of dietary n-6 and n-3 polyunsaturated fatty acids (PUFA) on cellular functions are not completely understood. In this study, we investigated the effects of these two types of PUFA on ionized calcium (Co 2+ ) fluxes in platelets. Adult male rats were fed either an n-6 PUFA-rich diet (corn oil, CO) or an n-3 PUFA-rich diet (menhaden oil, MO) for 8 to 12 days. Receptor-stimulated release and basal membrane fluxes of Ca 2+ were studied in platelets using two different reporter molecules. The fluorescent indicator chlorotetracycline (CTC) was employed to investigate Ca 2+ mobilization from internal storage compartments upon stimulation. Aequorin, a photoprotein, was used to monitor calcium movements through platelet membranes. Platelets with n-3 PUFA in membrane lipids as a consequence of the MO diet demonstrated a delay in the mobilization of Co 2+ from intracellular stores in response to stimulation to several doses of thrombin compared with control platelets (CO). This delayed response was significantly different compared with that found for controls at the lowest dose of agonist (MO, 40.2 ±3.2 sec; CO, 28.5 .9 sec, mean EM, P = 0.02). Decay rates for aequorin in rat platelets were found to be linear for 30 min and were similar after exposure to either 0.75 or 1.5 mM external calcium. The rates in platelets from animals fed MO were significantly lower compared with those observed in platelets from the animals fed CO (```P`` = 0.003). The combined results with the reporter molecules suggest that incorporation of n-3 PUFA into membranes delays calcium release and flux under stimulated and basal conditions, respectively. Such alterations would contribute to changes in cellular responses and suggest additional actions of n-3 PUFA beyond those attributed to their inhibitory actions on eicosanoid production from n-6 PUFA.