Responses of the solitary olfactory receptor cell of the guinea pig.

Olfactory receptor cells were isolated from the nasal mucosa of the guinea pig, using enzymatic digestion and mechanical dissociation. Under a phase-contrast microscope, the cells can be readily distinguished from other tissues, because of morphological characteristics. The intracellular free calcium ion concentrations ([Ca2+]i) of these cells were determined using the Ca2+ sensitive dye fura-2 and digital imaging microscopy. In the presence of 1 microM ionomycin, calcium-ionophore, there was an irreversible increase in [Ca2+]i in all the cells. During prolonged stimulation by 10 mM n-Amyl acetate under standard conditions, 16 of the 40 isolated olfactory cells responded with [Ca2+]i. There was no evidence of any increase in [Ca2+]i in the olfactory receptor cells in nominally Ca2+ free solution and stimulated by amyl acetate. When 3 mM CaCl2 was added, the [Ca2+]i increased remarkably. When cells were stimulated with amyl acetate in a CaCl2-depleted extracellular fluid supplemented with 10 microM verapamil (an L-type voltage-dependent calcium channel antagonist), no change occurred in [Ca2+]i. The addition of CaCl2 to this fluid did not elevate [Ca2+]i, in any cell. This would suggest that the [Ca2+]i increase in the presence of amyl acetate may mainly depend on the influx of calcium from the extracellular space. Our finding that the influx of extracellular calcium into cells was suppressed by verapamil suggests that the calcium channel, which is opened by amyl acetate, is a voltage-dependent L-type Ca2+ channel.