Vasoactive intestinal polypeptide stimulates cyclic AMP production in mouse N1E-115 neuroblastoma cells: modulation by a protein kinase C activator and ionomycin

Differential modulation of nucleoside transport types in neuroblastoma cells by protein kinase activation

Nucleoside transport regulation in undifferentiated Neuro-2A cells has been studied and found to include Na+-dependent adenosine transport and facilitated diffusion adenosine transport. The latter corresponded to nitrobenzylthioinosine-sensitive nucleoside transport. Short-term treatment of Neuro-2A cells with physiologically relevant signals only modulated the facilitated diffusion component. The stimulation of undifferentiated cells with forskolin or other activators of the protein kinase A pathway, decreased NBTI-sensitive adenosine transport. Treatment of cells with an inactive analogue of forskolin, 1,9-dideoxi-forskolin, had no effect on NBTI-sensitive nucleoside transport. Therefore, the inhibition of protein kinase A activity by pre-incubation with H-89 or the cAMP antagonist, Rp-8-Br-cAMPS, completely prevented the inhibitory effect of forskolin. Similarly, the activation of protein kinase C with phorbol 12,13-dibutyrate (PDBu) and the calcium ionophore A-23187 decreased NBTI-sensitive adenosine transport. The effect of PDBu was reversed by pre-incubation of cells with staurosporine. Maximal transport inhibition was obtained by the simultaneous stimulation of cells with a phorbol ester and A-23187 or a phorbol ester and forskolin. The modulation of NBTI-sensitive nucleoside transport corresponded to changes in specific [3H]NBTI binding to Neuro-2A cells. Maximal inhibition correlated well with a maximal enhancement of cAMP production. However, the Na+-dependent adenosine transport in Neuro-2A cells was not modulated by any of these signals.

Coordinated role of vasoactive intestinal peptide and nitric oxide in cardioprotection

The present study sought to examine the interrelationship between nitric oxide (NO) and vasoactive intestinal peptide (VIP) in myocardial protection. Isolated rat hearts were perfused for 15 min with buffer only (Group I); 0.3 mM VIP (Group II); 3 mM L-arginine (a precursor of NO) (Group III); VIP and aminoguanidine (iNOS blocker) (Group IV); or L-arginine plus VIP 10-28 (VIP inhibitor) (Group V). Each heart was then made globally ischemic for 30 min followed by 2 h reperfusion. Both VIP and NO were found to provide cardioprotection during ischemia and reperfusion. However, the beneficial effects of VIP and NO were reduced by inhibition of NO and VIP, respectively, suggesting that cardioprotection by VIP is modulated by NO and vice versa. The results of this study suggested a coordinated regulation by cardioprotection by NO and VIP.

Vasoactive intestinal peptide: mediator of laminin synthesis in cultured Schwann cells

To learn more about neuropeptide-induced glial responses which accompany axon regeneration, we studied effects of VIP on laminin production by cultured Schwann cells. Schwann cells were isolated from sciatic nerves of neonatal mice, purified, and incubated for 5 days in either control medium (DMEM + 15% FCS) or control medium containing 10-7 -10-11 M VIP. At 10-7 and 10-8 M VIP, laminin levels measured by enzyme-linked immunosorbent assay were significantly higher (55% and 35%) than those in control cultures. Lower VIP concentrations (10-9 -10-11 M) produced smaller increases which were not significant. Low-affinity VIP receptors which mediated this effect were demonstrated on Schwann cells by radioligand binding studies. The increased Schwann cell synthesis of laminin induced by VIP was blocked when either a VIP antagonist or a VIP receptor antagonist was added to the VIP-containing incubation medium. In contrast to astrocytes, when Schwann cells were loaded with fura-2, VIP did not increase cytosolic Ca2+. This indicates that Schwann cells and astrocytes may have different intracellular transduction pathways; their receptor subtypes also may differ. We suggest that the VIP-induced increase in laminin synthesis which we have observed in cultured Schwann cells may also occur in vivo and might be an important component of axon-Schwann cell interactions during nerve regeneration.