Odorants suppress T- and L-type Ca2+ currents in olfactory receptor cells by shifting their inactivation curves to a negative voltage

Mechanisms underlying suppression of T- and L-type Ca2+ currents (I-Ca,I-T and I-Ca,I-L) by odorants were investigated in newt olfactory receptor cell s (ORCs) using the whole-cell version of the patch-clamp technique. Under v oltage clamp, odorants (amyl acetate, limonene and acetophenone) reversibly suppressed I-Ca,I-T and I-Ca,I-L. These currents disappeared completely wi thin 150 ms following amyl acetate puffs, and recovered in approximately 1 s after the washout. Hyperpolarization of the membrane greatly relieved the odorant block of I-Ca,I-T and I-Ca,I-L. The activation curves of both curr ents were not changed significantly by odorants, while their inactivation c urves were shifted to negative voltages. Half-inactivation voltages of I-Ca ,I-T were - 66 mV(control), - 102 mV (amyl acetate), - 101 mV (limonene) an d - 105 mV (acetophenone) (all 0.3 mM); those of I-Ca,I-L were - 33 mV (con trol), - 61 mV (amyl acetate), - 59 mV (limonene), and - 63 mV (acetophenon e) tall 0.3 mM). These phenomena are similar to the effects of local anesth etics on I-Ca in various preparations and also similar to the effects of od orants on I-Na in ORCs, suggesting that these types of suppression are caus ed by the same mechanism. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.