2-Chloroadenosine reduces the N calcium current of cultured mouse sensory neurones in a pertussis toxin-sensitive manner.
1. The adenosine analogue 2-chloroadenosine (CADO) reduced the duration of calcium-dependent action potentials (CAPs) in mouse dorsal root ganglion (DRG) neurones in culture, by reducing voltage-activated calcium conductance (Macdonald, Skerritt & Werz, 1986). Using the single-electrode voltage clamp technique, we recorded three calcium current components in these neurones, the transient low-threshold (T), transient high-threshold (N) and slowly inactivating high-threshold (L) currents, as described previously (Nowycky, Fox & Tsien, 1985; Gross & Macdonald, 1987). CADO (100 microM) had no effect on the isolated T and L currents. In contrast, CADO reduced calcium currents evoked at clamp potentials positive to -20 mV from holding potentials (Vh) near the resting membrane potential; under these conditions, the calcium current consisted primarily of N and L calcium current components. 2. This effect of CADO was not voltage dependent. CADO reduced the magnitude of the calcium current without affecting the voltage dependence of the calcium current-voltage relation. In addition, similar reductions of calcium current were observed when currents were evoked from Vh of -60 or -80 mV. 3. In order to determine if a guanine nucleotide-binding (G) protein was involved in the CADO effect on calcium current, cultures were pre-treated with pertussis toxin (PT) for at least four hours. PT (100 ng/ml) reduced or abolished the CADO-induced reduction of CAP duration and calcium current. 4. Since CADO inhibits adenylate cyclase through the PT-sensitive G protein, Gi, we compared the effects of CADO and 8-Br-adenosine 3',5'-cyclic-monophosphate (8-Br-cyclic AMP) on calcium current. The effect of 8-Br-cyclic AMP was voltage dependent, unlike that of CADO. 8-Br-cyclic AMP reduced calcium currents evoked from Vh = -65 mV, but had no effect on currents evoked from Vh = -85 mV. 5. We conclude that the adenosine agonist CADO reduced CAP duration in mouse DRG neurones by selectively reducing the N current component, and that the coupling between the adenosine receptor and the calcium channel required a PT-sensitive G protein. The CADO effect was unlikely, however, to be due to modulation of adenylate cyclase activity.
Gross
R A
RA
Department of Neurology, University of Michigan, Ann Arbor 48104.
Macdonald
R L
RL
Ryan-Jastrow
T
T
D015762:2-Chloroadenosine / Q000494:pharmacology*; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D037361:Adenylate Cyclase Toxin; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D003864:Depression, Chemical; D005727:Ganglia, Spinal / Q000502:physiology*; D051379:Mice; D009125:Muscle Relaxants, Central / Q000494:pharmacology*; D009475:Neurons, Afferent / Q000187:drug effects*; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D009125:Muscle Relaxants, Central; D010566:Virulence Factors, Bordetella; D015762:2-Chloroadenosine; D015124:8-Bromo Cyclic Adenosine Monophosphate; D037342:Pertussis Toxin; D002118:Calcium