Effect of quinine solutions on intracellular Ca²⁺ levels in neuro-2a cells - Conventional physiological method for the evaluation of bitterness

The purpose of the present study was to examine the effect of quinine on intracellular Ca²⁺ ([Ca²⁺]_i) levels in cultured neuro-2a cells, and to investigate the possibility of using [Ca ²⁺]_i levels to predict the bitterness of quinine solutions. [Ca²⁺]_i levels in neuro-2a cells increased following stimulation by quinine in a concentration-related manner. There was a good linear correlationship between the quinine-induced increase in [Ca ²⁺]_i levels increase and the bitterness scores of the quinine solutions as assessed in human gustatory sensation tests (r ²=0.918). The quinine-induced increase in [Ca²⁺] _i levels was inhibited by thapsigargin (an inhibitor of the Ca ²⁺ pump into intracellular stores), U73122 (an inhibitor of phospholipase C) and ω-conotoxin (an N-type Ca²⁺-channel blocker), but not by nifedipine (an L-type Ca²⁺-channel blocker).