Characterizing voltage-dependent Ca(2+) channels coupled to VIP release and NO synthesis in enteric synaptosomes.
In enteric synaptosomes of the rat, the role of voltage-dependent Ca(2+) channels in K(+)-induced VIP release and nitric oxide (NO) synthesis was investigated. Basal VIP release was 39 +/- 4 pg/mg, and cofactor-substituted NO synthase activity was 7.0 +/- 0.8 fmol. mg(-1). min(-1). K(+) depolarization (65 mM) stimulated VIP release Ca(2+) dependently (basal, 100%; K(+), 172.2 +/- 16.2%; P < 0.05, n = 5). K(+)-stimulated VIP release was reduced by blockers of the P-type (omega-agatoxin-IVA, 3 x 10(-8) M) and N-type (omega-conotoxin-GVIA, 10(-6) M) Ca(2+) channels by ~50 and 25%, respectively, but not by blockers of the L-type (isradipine, 10(-8) M), Q-type (omega-conotoxin-MVIIC, 10(-6) M), or T-type (Ni(2+), 10(-6) M) Ca(2+) channels. In contrast, NO synthesis was suppressed by omega-agatoxin-IVA, omega-conotoxin-GVIA, and isradipine by ~79, 70, and 70%, respectively, whereas Ni(2+) and omega-conotoxin-MVIIC had no effect. These findings are suggestive of a coupling of depolarization-induced VIP release primarily to the P- and N-type Ca(2+) channels, whereas NO synthesis is presumably dependent on Ca(2+) influx not only via the P- and N- but also via the L-type Ca(2+) channel. In contrast, none of the Ca(2+) channel blockers affected VIP release evoked by exogenous NO, suggesting that NO induces VIP secretion by a different mechanism, presumably involving intracellular Ca(2+) stores.
Kurjak
M
M
Department of Internal Medicine II, Technical University Munich, 81675 Munich, Germany. manfred.kurjak@lrz.tu-muenchen.de
Sennefelder
A
A
Aigner
M
M
Schusdziarra
V
V
Allescher
H D
HD
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D008297:Male; D009569:Nitric Oxide / Q000096:biosynthesis* / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; D019001:Nitric Oxide Synthase; D011188:Potassium