Effects of alpha- and beta-adrenoceptor agonists and antagonists on ATP and catecholamine release and desensitization of the nicotinic response in bovine adrenal chromaffin cells.
The effects of a number of alpha- and beta-adrenoceptor agonists and antagonists on the modulation of secretion from bovine adrenal chromaffin cells were investigated. Secretion was induced by nicotine, 56 mM K+, histamine or Ba2+ and was detected by the ATP luciferin-luciferase bioluminescence technique or by the measurement of endogenous catecholamines (CA) by HPLC coupled with electrochemical detection. ATP release from freshly isolated cells by 5 microM nicotine was only weakly inhibited by adrenaline and noradrenaline and even then required high concentrations (greater than 500 microM), while dopamine (1 microM-1 mM) and isoproterenol (100 microM) had no effect. Clonidine (100 microM), oxymetazoline (100 microM), yohimbine (100 microM), and propranolol (5 microM) all produced inhibition of nicotine-induced ATP release with the order of potency:propranolol greater than oxymetazoline greater than clonidine = yohimbine. The inhibitory effect by propranolol could not be reversed by high concentrations of adrenaline or isoproterenol. In chromaffin cell monolayer cultures, all alpha 2-adrenoceptor agents tested (clonidine, oxymetazoline and yohimbine), produced a dose-dependent, Na+-sensitive, non-competitive inhibition of nicotine-induced catecholamine release with little effect on the catecholamine release induced by K+ (56 mM), histamine (10 microM) or Ba2+ (2.2 mM). (+/-)Propranolol caused a similar pattern of inhibition, however, this inhibition was also observed by (+)propranolol, an isomer with little beta-adrenoceptor antagonist activity. The effects of clonidine and propranolol on desensitization of nicotine-induced CA secretion were also investigated. The degree of desensitization of the nicotinic response was dependent on the concentration of nicotine to which the cells were pre-exposed. Desensitization was detected as the decrease in response to a near EC50 concentration of nicotine (5 microM) following pre-incubation of cells to nicotine in the range of 0.3-300 microM. The desensitization had a threshold of 1 microM nicotine and was maximal at 3 microM nicotine in the pre-incubation. Both clonidine (50 microM) and (+/-)propranolol (5 microM) inhibited CA secretion induced by nicotine (0.3 microM-300 microM) during the pre-incubation period. However, regardless of this inhibition of secretion, neither clonidine nor propranolol had an effect on either the onset, or the rate of nicotine-evoked desensitization subsequently observed. These data suggest that inhibition of the nicotinic response and desensitization of the nicotinic response are regulated independently.(ABSTRACT TRUNCATED AT 400 WORDS)
Wan
D C
DC
Department of Biochemistry, University of Melbourne, Parkville, Victoria, Australia.
Powis
D A
DA
Marley
P D
PD
Livett
B G
BG
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects; D002838:Chromaffin System / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D009538:Nicotine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000187:drug effects*; D012964:Sodium / Q000494:pharmacology
D002395:Catecholamines; D011941:Receptors, Adrenergic; D001464:Barium; D009538:Nicotine; D006632:Histamine; D000255:Adenosine Triphosphate; D012964:Sodium; D011433:Propranolol; D003000:Clonidine; D011188:Potassium; D002118:Calcium