Intracellular calcium kinetics after odorant stimulus in olfactory receptor cells isolated from mice

cAMP and IP3 act as secondary messengers in olfactory signal transduction and when activated, stimulate calcium levels in olfactory receptor cells. Little is known however, about the causal mechanism. We studied calcium kinetics in mouse olfactory receptor cells after odorant stimuli. Olfactory receptor cells were isolated from female BALB/c mice, treted with trypsin, and stained with Fura-2/AM. Changes in intracellular Ca2+ concentrations in stained cells were measured with a fluorescent microscopic image-processing device (ARGUS-50; Hamamatsu Photonix, Japan). We found that intracellular Ca2+ concentrations rose after exposure to a set of odorants, including 3-ethoxy-4-hydroxy-benzaldehyde, caprylic acid, heptanoic acid, nonanoic acid, eugenol, phenethyl alcohol, and n-amyl acetate. Adding 2', 5'-dideoxyadenosine, a cAMP inhibitor, beforehand suppressed olfactory receptor cell response to odorants. Intracellular Ca2+ concentrations increased substantially in response to stimulation by odorants in calcium-free Ringer's solution, but only a slight increase was seen in intracellular calcium concentration in response stimulation by a high concentration of K+ (145.6 mM) in calcium-free Ringer's solution. The increase in intracellular Ca2+ concentration after odorant stimuli was suppressed when olfactory receptor cells were pretreated with ryanodine, which releases Ca2+ from intracellular stores. These findings suggest that elevated Ca2+ concentrations may be involved in releasing Ca2+ from intracellular calcium stores in mouse olfactory receptor cells, in which cAMP functions as a secondary messenger in olfactory signal transduction.