Characterization of CCK(A) receptor affinity states and Ca(2+) signal transduction in vagal nodose ganglia.
CCK(A) receptors are present on vagal afferent fibers. The objectives of this study were to identify the presence of high- and low-affinity CCK(A) receptors on nodose ganglia and to characterize the intracellular calcium signal transduction activated by CCK. Stimulation of acutely isolated nodose ganglion cells from rats with 1 nM CCK-8 primarily evoked a Ca(2+) transient followed by a sustained Ca(2+) plateau (45% of cells responded), whereas 10 pM CCK-8 evoked Ca(2+) oscillations (37% of cells responded). CCK-OPE, a high-affinity agonist and low-affinity antagonist of CCK(A) receptors, primarily elicited Ca(2+) oscillations (29% of cells responded). CCK-OPE inhibited the Ca(2+) transient induced by 1 nM CCK-8 but not by carbachol and high K(+). This result suggests the presence of high- and low-affinity states of CCK(A) receptors on nodose ganglia. We further demonstrated that nicardipine (10 microM) but not omega-conotoxins GVIA and MVIIC (10-100 nM) abolished Ca(2+) signaling induced by CCK-8, indicating that an L-type voltage-dependent Ca(2+) channel and not an N- or Q-type Ca(2+) channel is coupled to CCK(A) receptors. In a separate study, we showed that the G protein activator NaF (10 mM) elicited a Ca(2+) transient and inhibited CCK-8-evoked Ca(2+) signaling, indicative of G protein(s) involvement in CCK(A) receptor activity. The G(q) protein antagonist Gp antagonist-2A (10 microM) also abolished the action of CCK-8. This study indicates that CCK(A) receptors exist in both high- and low-affinity states in the nodose ganglia. Activation of high-affinity CCK(A) receptors elicits Ca(2+) oscillations, whereas stimulation of low-affinity CCK(A) receptors evokes a sustained Ca(2+) plateau. These Ca(2+)-signaling modes are mediated through the L-type Ca(2+) channel and involve the participation of G(q) protein.
Lankisch
Tim O
TO
Gastroenterology Research Unit, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA.
Tsunoda
Yasuhiro
Y
Lu
Yuanxu
Y
Owyang
Chung
C
D000345:Affinity Labels / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000378:metabolism; D008297:Male; D009620:Nodose Ganglion / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043886:Receptor, Cholecystokinin A; D011949:Receptors, Cholecystokinin / Q000378:metabolism*; D012844:Sincalide / Q000031:analogs & derivatives* / Q000494:pharmacology
D000345:Affinity Labels; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D010446:Peptide Fragments; D043886:Receptor, Cholecystokinin A; D011949:Receptors, Cholecystokinin; C067408:cholecystokinin (26-32), Tyr-Gly-Nle(28,31) phenethyl ester-; D019204:GTP-Binding Proteins; D012844:Sincalide; D002118:Calcium