Cholecystokinin-8S-induced intracellular calcium signaling in acutely isolated periaqueductal gray neurons of the rat.
Many behavior studies indicate that cholecystokinin (CCK) is related to nociception and anxiety/panic actions in the midbrain periaqueductal gray (PAG). We previously reported that a sulfated form of CCK octapeptide (CCK-8S) produced excitatory effects at both pre- and postsynaptic loci in PAG neurons using slice preparations and whole-cell patch-clamp recordings. Here, we further examined the detailed mechanism of CCK-8S in acutely isolated PAG neurons of the rat using fura-2-based imaging of intracellular Ca2+ concentration ([Ca2+]i) and whole-cell patch-clamp recordings. Application of 1 microM CCK-8S produced an increase of [Ca2+]i, and its effect did not desensitize. This CCK-8S-induced [Ca2+]i increase was inhibited by the CCK2 receptor antagonist L-365260 but not by the CCK1 receptor antagonist L-364718. In addition, the effect of CCK-8S was eliminated by removing extracellular Ca2+, but not by an addition of the intracellular Ca2+ reuptake inhibitor thapsigargin. When simultaneous recordings of [Ca2+]i imaging and whole-cell patch-clamp were performed, CCK-8S-induced [Ca2+]i increase was significantly reduced at a membrane holding potential of -60 mV while CCK-8S-induced inward current was still observed. Current-voltage plots revealed that CCK-8S-induced inward current reversed near the equilibrium potential for K+ ions with a decreased membrane conductance. However, CCK-8S produced a significant inhibition on high-voltage-activated Ca2+ channel currents. These results suggest that CCK-8S can excite PAG neurons by inhibiting K+ channels, and CCK-8S-induced [Ca2+]i increase occurs secondary to depolarization. The evidence presented here expands our understanding of cellular mechanisms for CCK-mediated anti-analgesic and anxiogenic actions in the PAG.
Yang
Yu-Mi
YM
Biomedical Research Center, Korea Institute of Science and Technology (KIST), Seoul, Korea.
Chung
Jun-Mo
JM
Rhim
Hyewhon
H
D000818:Animals; D001570:Benzodiazepinones / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D010487:Periaqueductal Gray / Q000166:cytology / Q000502:physiology; D010671:Phenylurea Compounds / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043887:Receptor, Cholecystokinin B / Q000037:antagonists & inhibitors; D012844:Sincalide / Q000494:pharmacology*; D019284:Thapsigargin / Q000494:pharmacology
D001570:Benzodiazepinones; D010671:Phenylurea Compounds; D043887:Receptor, Cholecystokinin B; C058121:L 365260; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D012844:Sincalide