Effects of the endogenous cannabinoid anandamide on voltage-dependent sodium and calcium channels in rat ventricular myocytes

BACKGROUND AND PURPOSE The endocannabinoid anandamide (N-arachidonoyl ethanolamide; AEA) exerts negative inotropic and antiarrhythmic effects in ventricular myocytes. EXPERIMENTAL APPROACH Whole-cell patch-clamp technique and radioligand-binding methods were used to analyse the effects of anandamide in rat ventricular myocytes. KEY RESULTS In the presence of 1-10 M AEA, suppression of both Na+ and L-type Ca2+ channels was observed. Inhibition of Na+ channels was voltage and Pertussis toxin (PTX) - independent. Radioligand-binding studies indicated that specific binding of [H-3] batrachotoxin (BTX) to ventricular muscle membranes was also inhibited significantly by 10 mu M metAEA, a non-metabolized AEA analogue, with a marked decrease in B-max values but no change in K-d. Further studies on L-type Ca2+ channels indicated that AEA potently inhibited these channels (IC50 0.1 mu M) in a voltage-and PTX-independent manner. AEA inhibited maximal amplitudes without affecting the kinetics of Ba2+ currents. MetAEA also inhibited Na+ and L-type Ca2+ currents. Radioligand studies indicated that specific binding of [H-3]isradipine, was inhibited significantly by metAEA. (10 mu M), changing B-max but not K-d. CONCLUSION AND IMPLICATIONS Results indicate that AEA inhibited the function of voltage-dependent Na+ and L-type Ca2+ channels in rat ventricular myocytes, independent of CB1 and CB2 receptor activation.