Cyclic GMP-gated channels in a sympathetic neuron cell line.
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.
Thompson
S H
SH
Department of Biological Sciences and the Hopkins Marine Station, Stanford University, Pacific Grove, California 93950, USA. stuartt@leland.stanford.edu
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000166:cytology / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology; D001932:Brain Neoplasms / Q000378:metabolism; D002460:Cell Line; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D015222:Sodium Channels; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016276:8-bromocyclic GMP; D006152:Cyclic GMP