IP3-gated channels and their occurrence relative to CNG channels in the soma and dendritic knob of rat olfactory receptor neurons.
Olfactory receptor neurons respond to odorants with G protein-mediated increases in the concentrations of cyclic adenosine 3',5'-monophosphate (cAMP) and/or inositol-1,4,5-trisphosphate (IP3). This study provides evidence that both second messengers can directly activate distinct ion channels in excised inside-out patches from the dendritic knob and soma membrane of rat olfactory receptor neurons (ORNs). The IP3-gated channels in the dendritic knob and soma membranes could be classified into two types, with conductances of 40 +/- 7 pS (n = 5) and 14 +/- 3 pS (n = 4), with the former having longer open dwell times. Estimated values of the densities of both channels from the same inside-out membrane patches were very much smaller for IP3-gated than for CNG channels. For example, in the dendritic knob membrane there were about 1000 CNG channels x microm(-2) compared to about 85 IP3-gated channels x microm(-2). Furthermore, only about 36% of the dendritic knob patches responded to IP3, whereas 83% of the same patches responded to cAMP. In the soma, both channel densities were lower, with the CNG channel density again being larger ( approximately 57 channels x microm(-2)) than that of the IP3-gated channels ( approximately 13 channels x microm(-2)), with again a much smaller fraction of patches responding to IP3 than to cAMP. These results were consistent with other evidence suggesting that the cAMP-pathway dominates the IP3 pathway in mammalian olfactory transduction.
Kaur
R
R
School of Physiology and Pharmacology, The University of New South Wales, Sydney 2052, Australia.
Zhu
X O
XO
Moorhouse
A J
AJ
Barry
P H
PH
D000818:Animals; D015220:Calcium Channels / Q000032:analysis / Q000378:metabolism*; D020013:Calcium Signaling; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism*; D003712:Dendrites / Q000737:chemistry / Q000378:metabolism*; D004553:Electric Conductivity; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015640:Ion Channel Gating; D007473:Ion Channels / Q000032:analysis / Q000378:metabolism*; D018034:Olfactory Receptor Neurons / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis / Q000378:metabolism*; D012430:Ruthenium Red; D012903:Smell / Q000502:physiology
D015220:Calcium Channels; D054815:Cyclic Nucleotide-Gated Cation Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007473:Ion Channels; D018160:Receptors, Cytoplasmic and Nuclear; D012430:Ruthenium Red; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP