Inhibitory effects of caffeine on secretagogue-induced catecholamine secretion from adrenal chromaffin cells of the guinea-pig.
1. The inhibitory action of caffeine on catecholamine secretion induced by secretagogues was investigated in perfused adrenal glands and dispersed chromaffin cells of the guinea-pig. 2. Caffeine (10 mM) caused a reversible inhibition of catecholamine secretion evoked by acetylcholine (ACh, 50 microM), KCl (56 mM, high K+) and veratridine (100 microM) and that induced by muscarinic receptor activation in the absence of extracellular Ca2+ in perfused adrenal glands. 3. In dispersed chromaffin cells, caffeine caused a dose-dependent inhibition of the secretory responses to 100 microM ACh and veratridine. Forskolin (30 microM), dibutyryl cyclic AMP (1 mM) and 8-bromo cyclic AMP (1 mM) did not mimic the action of caffeine. 4. In the voltage-clamp, whole-cell recording mode (at a holding potential of -60 mV or -70 mV), ACh (100 microM) evoked an inward current, and depolarizing pulses elicited inward Na+, Ca2+ and outward K+ currents. All these responses were partially inhibited by caffeine (20 mM). 5. ACh rapidly increased the intracellular concentration of Ca2+ ([Ca2+]i) in fura-2-loaded cells in either the presence or the absence of external Ca2+, though its magnitude was decreased by about 50% in Ca(2+)-free conditions. Caffeine (20 mM) inhibited these ACh-induced increases in [Ca2+]i. 6. In permeabilized chromaffin cells, caffeine (20 mM) caused an inhibition of catecholamine secretion evoked by Ca2+ (10 microM). 7. These results suggest that caffeine inhibits evoked catecholamine secretion through mechanisms such as the blockade of voltage-dependent Na+ and Ca2+ currents and ACh receptor current, and reduction of the release of intracellularly stored Ca2+ and/or Ca(2+)-sensitivity of the secretory apparatus.
Nakazato
Y
Y
Department of Pharmacology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
Tani
Y
Y
Teraoka
H
H
Sugawara
T
T
Asano
T
T
Ohta
T
T
Ito
S
S
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000311:Adrenal Glands / Q000187:drug effects* / Q000378:metabolism*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D005260:Female; D016257:Fura-2; D006168:Guinea Pigs; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D012636:Secretory Rate / Q000187:drug effects; D012680:Sensitivity and Specificity; D014701:Veratridine / Q000494:pharmacology
D002395:Catecholamines; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D002110:Caffeine; D003994:Bucladesine; D014701:Veratridine; D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2