8-bromocyclic-gmp and Brain-Neoplasms

Intracarotid infusion of bradykinin and its analogue, RMP-7, selectively increase the permeability of brain tumor capillaries though the nitrix oxide (NO) and cyclic GMP pathway. Maximum blood-tumor barrier (BTB) permeability induced by bradykinin is observed at 15 min after intracarotid infusion and this effect is decreased even if the infusion continues. The mechanism for this decreased effect with long term infusion has not been clearly defined. This study sought to determine the involvement of the NO-cyclic GMP pathway in this event. Regional permeability was investigated in 44 Wistar rats with implanted RG2 gliomas, using quantitative autoradiography to determine the unidirectional transfer constant (Ki) of radiolabeled 14C-dextran. Tumor bearing rats were treated by intracarotid infusion of bradykinin (10 micrograms kg-1 min-1) with or without pretreatment with bradykinin, the NO donor s-nitrosoglutathione (10 nmol kg-1 min-1), or the cyclic GMP analogue, 8Br-cyclic GMP (200 micrograms kg-1 min-1). At 30 min of bradykinin infusion, BTB permeability was significantly lower compared to 15 min of bradykinin infusion (3.79 +/- 0.99 vs. 16.20 +/- 3.43 microliters g-1 min-1, p < 0.001). Pretreatment with an NO donor significantly decreased BTB permeability in bradykinin infused rats (5.09 +/- 2.61 vs. 13.51 +/- 4.19 microliters g-1 min-1, p < 0.001), as did pretreatment with a cyclic GMP analogue (4.48 +/- 0.95 vs. 12.31 +/- 3.90 microliters g-1 min-1, p < 0.001). There was no increased permeability in nontumor brain areas. Increased tumor permeability by bradykinin appears to be regulated by NO and cyclic GMP which are second messengers involved in the bradykinin B2 receptor mediated cascade.

Topics: Animals; Bradykinin; Brain Neoplasms; Capillary Permeability; Cyclic GMP; Drug Resistance; Female; Glioma; Glutathione; Nitric Oxide; Nitroso Compounds; Rats; Rats, Wistar; S-Nitrosoglutathione

The stimulation of IP3 production by muscarinic agonists causes both intracellular Ca2+ release and activation of a voltage-independent cation current in differentiated N1E-115 cells, a neuroblastoma cell line derived from mouse sympathetic ganglia. Earlier work showed that the membrane current requires an increase in 3',5'-cyclic guanosine monophosphate (cGMP) produced through the NO-synthase/guanylyl cyclase cascade and suggested that the cells may express cyclic nucleotide-gated ion channels. This was tested using patch clamp methods. The membrane permeable cGMP analogue, 8-br-cGMP, activates Na+ permeable channels in cell attached patches. Single channel currents were recorded in excised patches bathed in symmetrical Na+ solutions. cGMP-dependent single channel activity consists of prolonged bursts of rapid openings and closings that continue without desensitization. The rate of occurrence of bursts as well as the burst length increase with cGMP concentration. The unitary conductance in symmetrical 160 mM Na+ is 47 pS and is independent of voltage in the range -50 to +50 mV. There is no apparent effect of voltage on opening probability. The dose response curve relating cGMP concentration to channel opening probability is fit by the Hill equation assuming an apparent KD of 10 microm and a Hill coefficient of 2. In contrast, cAMP failed to activate the channel at concentrations as high as 100 microm. Cyclic nucleotide gated (CNG) channels in N1E-115 cells share a number of properties with CNG channels in sensory receptors. Their presence in neuronal cells provides a mechanism by which activation of the NO/cGMP pathway by G-protein-coupled neurotransmitter receptors can directly modify Ca2+ influx and electrical excitability. In N1E-115 cells, Ca2+ entry by this pathway is necessary to refill the IP3-sensitive intracellular Ca2+ pool during repeated stimulation and CNG channels may play a similar role in other neurons.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Brain; Brain Chemistry; Brain Neoplasms; Cell Line; Cyclic GMP; Ganglia, Sympathetic; Ion Channel Gating; Membrane Potentials; Mice; Neuroblastoma; Neurons; Patch-Clamp Techniques; Sodium Channels; Sympathetic Nervous System