Mechanical activation of dorsal root ganglion cells in vitro: comparison with capsaicin and modulation by kappa-opioids.
The aim of this study was to characterize plasma membrane pathways involved in the intracellular calcium ([Ca(2+)](i)) response of small DRG neurons to mechanical stimulation and the modulation of these pathways by kappa-opioids. [Ca(2+)](i) responses were measured by fluorescence video microscopy of Fura-2 labeled lumbosacral DRG neurons obtained from adult rats in short-term primary culture. Transient focal mechanical stimulation of the soma, or brief superfusion with 300 nM capsaicin, resulted to [Ca(2+)](i) increases which were abolished in Ca(2+)-free solution, but unaffected by lanthanum (25 microM) or tetrodotoxin (10(-6) M). 156 out of 465 neurons tested (34%) showed mechanosensitivity while 55 out of 118 neurons (47%) were capsaicin-sensitive. Ninty percent of capsaicin-sensitive neurons were mechanosensitive. Gadolinium (Gd(3+); 250 microM) and amiloride (100 microM) abolished the [Ca(2+)](i) transient in response to mechanical stimulation, but had no effect on capsaicin-induced [Ca(2+)](i) transients. The kappa-opioid agonists U50,488 and fedotozine showed a dose-dependent inhibition of mechanically stimulated [Ca(2+)](i) transients but had little effect on capsaicin-induced [Ca(2+)](i) transients. The inhibitory effect of U50,488 was abolished by the kappa-opioid antagonist nor-Binaltorphimine dihydrochloride (nor-BNI; 100 nM), and by high concentrations of naloxone (30-100 nM), but not by low concentrations of naloxone (3 nM). We conclude that mechanically induced [Ca(2+)](i) transients in small diameter DRG somas are mediated by influx of Ca(2+) through a Gd(3+)- and amiloride-sensitive plasma membrane pathway that is co-expressed with capsaicin-sensitive channels. Mechanical-, but not capsaicin-mediated, Ca(2+) transients are sensitive to kappa-opioid agonists.
Gschossmann
J M
JM
CURE Digestive Diseases Research Center/Neuroenteric Disease Program, Department of Medicine, University of California, Los Angeles, Los Angeles CA, USA.
Chaban
V V
VV
McRoberts
J A
JA
Raybould
H E
HE
Young
S H
SH
Ennes
H S
HS
Lembo
T
T
Mayer
E A
EA
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001593:Benzyl Compounds / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology*; D002478:Cells, Cultured; D005682:Gadolinium / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010812:Physical Stimulation; D011437:Propylamines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017473:Receptors, Opioid, kappa / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*
D001593:Benzyl Compounds; D011437:Propylamines; D017473:Receptors, Opioid, kappa; C051844:norbinaltorphimine; D009271:Naltrexone; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000584:Amiloride; D005682:Gadolinium; C067749:fedotozine; D002211:Capsaicin; D002118:Calcium