Characterizing voltage-dependent Ca channels coupled to VIP release and NO synthesis in enteric synaptosomes

Kurjak, M., A. Sennefelder, M. Aigner, V. Schusdziarra, and H. D. Allescher. Characterizing voltage-dependent Ca2 channels coupled to VIP release and NO synthesis in enteric synaptosomes. Am J Physiol Gastrointest Liver Physiol 283: G1027–G1034, 2002. First published July 31, 2002; 10.1152/ajpgi.00400.2001.—In enteric synaptosomes of the rat, the role of voltage-dependent Ca2 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 Ca2 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 ( -agatoxin-IVA, 3 10 8 M) and N-type ( -conotoxin-GVIA, 10 6 M) Ca2 channels by 50 and 25%, respectively, but not by blockers of the L-type (isradipine, 10 8 M), Q-type ( -conotoxin-MVIIC, 10 6 M), or T-type (Ni2 , 10 6 M) Ca2 channels. In contrast, NO synthesis was suppressed by -agatoxin-IVA, -conotoxin-GVIA, and isradipine by 79, 70, and 70%, respectively, whereas Ni2 and -conotoxin-MVIIC had no effect. These findings are suggestive of a coupling of depolarization-induced VIP release primarily to the Pand N-type Ca2 channels, whereas NO synthesis is presumably dependent on Ca2 influx not only via the Pand Nbut also via the L-type Ca2 channel. In contrast, none of the Ca2 channel blockers affected VIP release evoked by exogenous NO, suggesting that NO induces VIP secretion by a different mechanism, presumably involving intracellular Ca2 stores.