Effects of quinine on the intracellular calcium level and membrane potential of PC 12 cultures

The mechanism for the perception of bitterness appears to be quite complicated, even for quinine, which is a model bitter substance, and thus has yet to be completely elucidated. To investigate the possibility of being able to predict the bitterness of quinine solutions, we examined the effects of quinine on intracellular calcium ion concentration ([Ca²⁺]i) and membrane potentials in PC 12 cultures. [Ca²⁺]i and membrane potentials were analysed by fluorescence confocal microscopic imaging using the Ca ²⁺-sensitive probe Calcium Green 1/AM and the membrane potential-sensitive probe bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC₄(3)). Quinine elicited an increase in the membrane potential along with a concentration-dependent increase in [Ca²⁺]i. These increases were inhibited by extracellular Ca²⁺-free conditions, thapsigargin, which is a Ca²⁺-pump inhibitor, and U73122, which is a phospholipase C inhibitor. The quinine-induced increase in [Ca²⁺]i levels was inhibited by nifedipine, an L-type Ca²⁺-channel blocker, ufconotoxin, a T-type Ca²⁺-channel blocker, and BMI-40, which is a bitterness-masking substance. These results suggest that responses in PC 12 cultures may be used as a simple model of bitterness perception.