Release of cholecystokinin-like immunoreactivity in the frontal cortex of conscious rats as assessed by transcerebral microdialysis: effects of different depolarizing stimuli.
The release of cholecystokinin-like immunoreactivity (CCK-LI) from the frontal cortex of freely moving rats has been studied using a transcerebral microdialysis technique coupled to a radioimmunoassay procedure. Basal levels of CCK-LI in the dialysate were above detection limits (2.4 +/- 0.7 pg/20 min; n = 8). High-K+ media evoked CCK-LI overflow in a concentration-dependent manner. The threshold concentration was 50 mM KCl. The peak overflow evoked by 100 mM K+ amounted to 42.7 +/- 2.8 pg/20 min (n = 6); it was totally Ca2+ dependent but insensitive to 1 microM tetrodotoxin. Infusion of 4-aminopyridine (1 mM; 20 min) evoked an overflow of CCK-LI (32 +/- 2.3 pg/20 min; n = 4), which was totally Ca2+ dependent and tetrodotoxin sensitive. Depolarization with 100 micrograms/ml of veratrine (20 min) provoked a CCK-LI overflow (62.2 +/- 10 pg/20 min; n = 6), which was also blocked by tetrodotoxin or by the absence of Ca2+ ions. The CCK-LI material collected under basal conditions or during veratrine infusion consisted essentially of CCK octapeptide sulfate. The veratrine-induced CCK-LI overflow did not change significantly when the infusion time was prolonged to 100 min. A second 20-min stimulus with 100 micrograms/ml of veratrine applied 200 min after a first 20-min stimulus evoked a barely significant CCK-LI overflow. These data suggest that one single 20-min stimulus with 100 micrograms/ml of veratrine may be sufficient to deplete the CCK-LI releasable stores and that > 200 min are required to replenish the depleted CCK-containing vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)
Vallebuona
F
F
Istituto di Farmacologia e Farmacognosia, Universitá degli Studi di Genova, Italy.
Paudice
P
P
Raiteri
M
M
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002766:Cholecystokinin / Q000378:metabolism*; D003956:Dialysis; D004594:Electrophysiology; D005625:Frontal Lobe / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013779:Tetrodotoxin / Q000494:pharmacology; D014702:Veratrine / Q000494:pharmacology
D013779:Tetrodotoxin; D002766:Cholecystokinin; D015761:4-Aminopyridine; D014702:Veratrine; D011188:Potassium; D002118:Calcium