INSP(3) CAUSES AN INCREASE IN APICAL [CA2-CELLS(](I) BY ACTIVATING 2 DISTINCT CURRENT COMPONENTS IN VERTEBRATE OLFACTORY RECEPTOR)

1. Effects of inositol-1,4,5-trisphosphate (InsP(3)) applied through a patch pipette to Xenopus laevis olfactory receptor cells (ORCs) were studied using the patch-clamp technique in conjunction with calcium im aging with fura-2. 2. InsP(3) activated, first, a novel voltage-indepe ndent Ca2+ current (I-Ca) and, second, a nonselective cation current ( I-cat). 3. The activation of these currents occurred at different intr acellular calcium concentrations, and the activation of either current led to a marked increase of [Ca2+](i) in the dendritic knob. 4. The r esults suggest that InsP(3) might act as a second messenger in vertebr ate olfactory receptor cells by activating, through different mechanis ms, a plasma membrane Ca2+ conductance (I-Ca) and a nonselective catio n conductance (I-cat).