Histamine H3-receptor-induced attenuation of norepinephrine exocytosis: a decreased protein kinase a activity mediates a reduction in intracellular calcium.
We had reported that activation of presynaptic histamine H(3)-receptors inhibits norepinephrine exocytosis from depolarized cardiac sympathetic nerve endings, an action associated with a marked decrease in intraneuronal Ca(2+) that we ascribed to a decreased Ca(2+) influx. An H(3)-receptor-mediated inhibition of cAMP-dependent phosphorylation of Ca(2+) channels could cause a sequential attenuation of Ca(2+) influx, intraneuronal Ca(2+) and norepinephrine exocytosis. We tested this hypothesis in sympathetic nerve endings (cardiac synaptosomes) expressing native H(3)-receptors and in human neuroblastoma SH-SY5Y cells transfected with H(3)-receptors. Norepinephrine exocytosis was elicited by K(+) or by stimulation of adenylyl cyclase with forskolin. H(3)-receptor activation markedly attenuated the K(+)- and forskolin-induced norepinephrine exocytosis; pretreatment with pertussis toxin prevented this effect. Similar to forskolin, 8-bromo-cAMP elicited norepinephrine exocytosis but, unlike forskolin, it was unaffected by H(3)-receptor activation, demonstrating that inhibition of adenylyl cyclase is a pivotal step in the H(3)-receptor transductional cascade. Indeed, we found that H(3)-receptor activation attenuated norepinephrine exocytosis concomitantly with a decrease in intracellular cAMP and PKA activity in SH-SY5Y-H(3) cells. Moreover, pharmacological PKA inhibition acted synergistically with H(3)-receptor activation to reduce K(+)-induced peak intracellular Ca(2+) in SH-SY5Y-H(3) cells and norepinephrine exocytosis in cardiac synaptosomes. Furthermore, H(3)-receptor activation synergized with N- and L-type Ca(2+) channel blockers to reduce norepinephrine exocytosis in cardiac synaptosomes. Our findings suggest that the H(3)-receptor-mediated inhibition of norepinephrine exocytosis from cardiac sympathetic nerves results sequentially from H(3)-receptor-G(i)/G(o) coupling, inhibition of adenylyl cyclase activity, and decreased cAMP formation, leading to diminished PKA activity, and thus, decreased Ca(2+) influx through voltage-operated Ca(2+) channels.
Seyedi
Nahid
N
Department of Pharmacology, 1300 York Ave., Weill Medical College of Cornell University, New York, NY 10021, USA.
Mackins
Christina J
CJ
Machida
Takuji
T
Reid
Alicia C
AC
Silver
Randi B
RB
Levi
Roberto
R
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D006168:Guinea Pigs; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D018100:Receptors, Histamine H3 / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism
D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D018100:Receptors, Histamine H3; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine