5'-(N-ethylcarboxamido)adenosine inhibits Ca2+ influx and activates a protein phosphatase in bovine adrenal chromaffin cells.
We investigated the effect of the adenosine receptor agonist 5'-(N-ethylcarboxamido)adenosine (NECA) in catecholamine secretion from adrenal chromaffin cells that exhibit only the A2b subtype adenosine receptor. NECA reduced catecholamine release evoked by the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) in a time-dependent manner. Inhibition reached 25% after 30-40-min exposure to NECA. This effect on DMPP-evoked catecholamine secretion was mirrored by a similar (27.7 +/- 3.3%), slowly developing inhibition of [Ca2+]i transients induced by DMPP that peaked at 30-min preincubation with NECA. The capacity of the chromaffin cells to buffer Ca2+ load was not affected by the treatment with NECA. Short-term treatment with NECA failed both to modify [Ca2+]i levels and to increase endogenous diacylglycerol production, showing that NECA does not activate the intracellular Ca2+/protein kinase C signaling pathway. The inhibitory effects of NECA were accompanied by a 30% increase of protein phosphatase activity in chromaffin cell cytosol. We suggest that dephosphorylation of a protein involved in DMPP-evoked Ca2+ influx pathway (e.g., L-type Ca2+ channels) could be the mechanism of the inhibitory action of adenosine receptor stimulation on catecholamine secretion from adrenal chromaffin cells.
Mateo
J
J
Departamento de Bioquímica y Biología Molecular, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
Castro
E
E
Zwiller
J
J
Aunis
D
D
Miras-Portugal
M T
MT
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D010749:Phosphoprotein Phosphatases / Q000378:metabolism* / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D013997:Time Factors; D014665:Vasodilator Agents / Q000494:pharmacology*
D002395:Catecholamines; D014665:Vasodilator Agents; D019830:Adenosine-5'-(N-ethylcarboxamide); D004246:Dimethylphenylpiperazinium Iodide; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D000241:Adenosine; D002118:Calcium