T-type Ca2+ channels contribute to IBMX/forskolin- and K(+)-induced Ca(2+) transients in porcine olfactory receptor neurons.
T-type Ca(2+) channels are low-voltage-activated Ca(2+) channels that control Ca(2+) entry in excitable cells during small depolarization above resting potentials. Using Ca(2+) imaging with a laser scanning confocal microscope we investigated the involvement of T-type Ca(2+) channels in IBMX/forskolin- and sparingly elevated extracellular K(+)-induced Ca(2+) transients in freshly isolated porcine olfactory receptor neurons (ORNs). In the presence of mibefradil (10microM) or Ni(2+) (100microM), the selective T-type Ca(2+) channel inhibitors, IBMX/forskolin-induced Ca(2+) transients in the soma were either strongly (>60%) inhibited or abolished completely. However, the Ca(2+) transients in the knob were only partially (<60%) inhibited. Ca(2+) transients induced by 30mM K(+) were also partially ( approximately 60%) inhibited at both the knob and soma. Furthermore, ORNs responded to as little as a 2.5mM increase in the extracellular K(+) concentration (7.5mM K(+)), and such responses were completely inhibited by mibefradil or Ni(2+). These results reveal functional expression of T-type Ca(2+) channels in porcine ORNs, and suggest a role for these channels in the spread Ca(2+) transients from the knob to the soma during activation of the cAMP cascade following odorant binding to G-protein-coupled receptors on the cilia/knob of ORNs.
Gautam
Shree Hari
SH
Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan.
Otsuguro
Ken-Ichi
K
Ito
Shigeo
S
Saito
Toshiyuki
T
Habara
Yoshiaki
Y
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020747:Calcium Channels, T-Type / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D008297:Male; D020748:Mibefradil / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D009830:Olfactory Bulb / Q000166:cytology; D018034:Olfactory Receptor Neurons / Q000187:drug effects / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D013552:Swine / Q000033:anatomy & histology / Q000502:physiology; D013997:Time Factors; D014966:Xanthenes / Q000378:metabolism
D000814:Aniline Compounds; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; C409648:Fluo 4; D010726:Phosphodiesterase Inhibitors; D014966:Xanthenes; D005576:Colforsin; D020748:Mibefradil; D011189:Potassium Chloride; D009532:Nickel; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine