Interacting effects of capsaicin and anandamide on intracellular calcium in sensory neurones

Capsaicin (100 nM to 1 mu M) and anandamide (200 nM to 10 mu M) caused a tr ansient increase in fluorescence of fura-2 loaded cultured small trigeminal neurones of rats measured with a ratiometric technique. The percentage of cells responding to capsaicin at 100 nM, 330 nM and 1 mu M was 47.4%, 45.3% , and 70.4%, respectively. Averaged peak value of fluorescense ratio (R) at 340 and 380 nm excitation was slightly dose dependent. Peaks of anandamide -induced transients were R = 0.2 at 200 nM and 0.16 at 10 mu M. Near 40% of capsaicin-sensitive cells responded also to anandamide. Anandamide (200 nM ) inhibited the capsaicin-induced calcium influx. The results suggest that anandamide increases intracellular calcium and inhibits capsaicin-evoked ca lcium transients. NeuroReport 11:1949-1952 (C) 2000 Lippincott Williams & W ilkins.