Guanosine-5'-O-(3-thiotriphosphate) modifies kinetics of voltage-dependent calcium current in chick sensory neurons.
Internal perfusion with the G-protein activator guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma S) mimics the effect of noradrenaline and dopamine on the voltage-dependent calcium current in chick dorsal root ganglion (DRG) cells. With 100 microM GTP-gamma S in the pipette, the current at +10 mV was depressed by approximately 50%, with a 10-fold increase of its time to peak. The activation time course of the control calcium current could be approximated with a single exponential curve, whereas with GTP-gamma S the activation time course was double exponential, with time constants tau 1 and tau 2. 2 mM Mg-ATP in the pipette prevented the GTP-gamma S-induced current decrease in 70% of the cells, but the time course of the current was always double exponential. From -50 mV, the current at +10 mV was best fitted with tau 1 = 1.7 +/- 0.5 and tau 2 = 25.6 +/- 5.5 in seven cells. Both time constants decreased with increasing depolarizations. In the first 2 min of recording, the current changed with time. However, both tau 1 and tau 2 were constant, whereas the relative contribution of the slow component increased from 10 to 70%. In addition, the effect was independent of the holding potential in the range from -100 to -30 mV. These results suggest that the activation of a G-protein causes a fraction of the high-threshold calcium channels to switch to a new closed state, with slower opening kinetics.
Marchetti
C
C
Istituto di Cibernetica e Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy.
Robello
M
M
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002642:Chick Embryo; D004553:Electric Conductivity; D005727:Ganglia, Spinal / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009475:Neurons, Afferent / Q000502:physiology*; D013873:Thionucleotides / Q000494:pharmacology*; D013997:Time Factors
D015220:Calcium Channels; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate