ω3 polyunsaturated fatty acid modulates dihydropyridine effects on L-type Ca²⁺ channels, cytosolic Ca²⁺, and contraction in adult rat cardiac myocytes

The effect of docosahexaenoic acid (DHA; C22:6) on dihydropyridine (DHP) interaction with L-type Ca²⁺ channel current (I_Ca), cytosolic Ca²⁺ (Ca_i), and cell contraction in isolated adult rat cardiac myocytes was studied. The DHP L-type Ca²⁺-channel blocker nitrendipine (10 nM) reduced peak I_Ca (measured by whole-cell voltage clamp from -45 to 0 mV) and reduced the amplitude of the Ca²⁺ transient (measured as the transient in indo-1 fluorescence, 410/490 nm) and the twitch amplitude (measured via photodiode array) during steady-state electrical stimulation (0.5 Hz). The DHP L-type Ca²⁺ channel agonist BAY K 8644 (10 nM) significantly increased I_Ca, the amplitude of the Ca_i transient, and contraction. When cells were exposed to DHA (5 μM) simultaneously with either BAY K 8644 or nitrendipine, the drug effects were abolished. Arachidonic acid (C20:4) at 5 μM did not block the inhibitory effects of nitrendipine nor did it prevent the potentiating effects of BAY K 8644. DHA modulation of DHP action could be reversed by cell perfusion with fatty acid-free bovine serum albumin at 1 mg/ml. Neither DHA nor arachidonic acid alone (5 μM) had any apparent effect on the parameters measured. DHA (5 μM) had no influence over β-adrenergic receptor stimulation (isoproterenol, 0.01-1 μM)-induced increases in I_Ca, Ca_i, or contraction. The findings that DHA inhibits the effect of DHP agonists and antagonists on Ca²⁺-channel current but has no effect alone or on β-adrenergic-induced increases in I_Ca suggests that DHA specifically binds to Ca²⁺ channels at or near DHP binding sites and interferes with I_Ca modulation.