Inhibition of the calcium-activated chloride current in cardiac ventricular myocytes by N-(p-amylcinnamoyl)anthranilic acid (ACA)

N-(p-amylcinnamoyl)anthranilic acid (ACA), a phospholipase A2 (PLA2) inhibitor, is structurally-related to non-steroidal anti-inflammatory drugs (NSAIDs) of the fenamate group and may also modulate various ion channels. We used the whole-cell, patch-clamp technique at room temperature to investigate the effects of ACA on the Ca2+-activated chloride current (ICl(Ca)) and other chloride currents in isolated pig cardiac ventricular myocytes. ACA reversibly inhibited ICl(Ca) in a concentration-dependent manner (IC50 = 4.2 μM, nHill = 1.1), without affecting the L-type Ca2+ current. Unlike ACA, the non-selective PLA2 inhibitor bromophenacyl bromide (BPB; 50 μM) had no effect on ICl(Ca). In addition, the analgesic NSAID structurally-related to ACA, diclofenac (50 μM) also had no effect on ICl(Ca), whereas the current in the same cells could be suppressed by chloride channel blockers flufenamic acid (FFA; 100 μM) or 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS;100 μM). Besides ICl(Ca), ACA (50 μM) also suppressed the cAMP-activated chloride current, but to a lesser extent. It is proposed that the inhibitory effects of ACA on ICl(Ca) are PLA2-independent and that the drug may serve as a useful tool in understanding the nature and function of cardiac anion channels.

Research highlights
► Pharmacological agents are major tools to study calcium-activated chloride channels.
► Specific blockers of calcium-activated chloride channels are needed.
► ACA is a potent calcium-activated chloride channel blocker, with no effect on calcium channels.