Inhibition of [Ca2+]i transients in rat adrenal chromaffin cells by neuropeptide Y: role for a cGMP-dependent protein kinase-activated K+ conductance.
The effects of neuropeptide Y on the intracellular level of Ca2+ ([Ca2+]i) were studied in cultured rat adrenal chromaffin cells loaded with fura-2. A proportion (16%) of cells exhibited spontaneous rhythmic [Ca2+]i oscillations. In silent cells, oscillations could be induced by forskolin and 1,9-dideoxyforskolin. This action of forskolin was not modified by H-89, an inhibitor of protein kinase A. Spontaneous [Ca2+]i fluctuations and [Ca2+]i fluctuations induced by forskolin- and 1,9-dideoxyforskolin were inhibited by neuropeptide Y. Increases in [Ca2+]i induced by 10 and 20 mM KCI but not by 50 mM KCI were diminished by neuropeptide Y. However, neuropeptide Y had no effect on [Ca2+]i increases evoked by (-)BAY K8644 and the inhibitory effect of neuropeptide Y on responses induced by 20 mM KCI was not modified by omega-conotoxin GVIA, consistent with neither L- nor N-type voltage-sensitive Ca2+ channels being affected by neuropeptide Y. Rises in [Ca2+]i provoked by 10 mM tetraethylammonium were not decreased by neuropeptide Y, suggesting that K+ channel blockade reduces the effect of neuropeptide Y. However, [Ca2+]i transients induced by 1 mM tetraethylammonium and charybdotoxin were still inhibited by neuropeptide Y, as were those to 20 mM KCI in the presence of apamin. The actions of neuropeptide Y on [Ca2+]i transients provoked by 20 and 50 mM KCI, 1 mM tetraethylammonium, (-)BAY K8644 and charybdotoxin were mimicked by 8-bromo-cGMP. In contrast, 8-bromo-cAMP did not modify responses to 20 mM KCI or 1 mM tetraethylammonium. The inhibitory effects of neuropeptide Y and 8-bromo-cGMP on increases in [Ca2+]i induced by 1 mM tetraethylammonium were abolished by the Rp-8-pCPT-cGMPS, an inhibitor of protein kinase G, but not by H-89. A rapid, transient increase in cGMP level was found in rat adrenal medullary tissues stimulated with 1 microM neuropeptide Y. Rises in [Ca2+]i produced by DMPP, a nicotinic agonist, but not by muscarine, were decreased by neuropeptide Y. Our data suggest that neuropeptide Y activates a K+ conductance via a protein kinase G-dependent pathway, thereby opposing the depolarizing action of K+ channel blocking agents and the associated rise in [Ca2+]i.
Lemos
V S
VS
Université Louis Pasteur de Strasbourg, Laboratoire de Pharmacologie et Physiopathologie Cellulaires-CNRS URA 600, Illkirch, France.
Bucher
B
B
Côrtes
S F
SF
Takeda
K
K
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000311:Adrenal Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D005576:Colforsin / Q000031:analogs & derivatives / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004594:Electrophysiology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D009478:Neuropeptide Y / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018679:Cholinergic Agonists; D009478:Neuropeptide Y; D015221:Potassium Channels; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D006152:Cyclic GMP; C047983:1,9-dideoxyforskolin; D011188:Potassium