title: Regulation by GTP and its stable thiol derivatives of calcium current components in rat nodose ganglion neurons.
abstract: The calcium current components of acutely dissociated nodose ganglion neurons were characterized using the whole-cell variation of the patch-clamp technique. Many neurotransmitters regulate neuronal calcium currents via GTP binding (G) proteins and in some cases affect calcium current components selectively. To determine whether G proteins regulated these current components in the absence of ligand binding, recording pipettes contained 0.1 mM GTP, guanosine 5'-O-(thiodiphosphate) (GDP-beta-S), or guanosine 5'-O-(thiotriphosphate) (GTP-gamma-S). Nodose ganglion neurons had three calcium current components, similar to T, N, and L current components found in other sensory neurons. Isolated T currents did not diminish in magnitude during a 20-min recording, but there was a progressive loss of currents containing the N and L current components. The reduction of current magnitude was primarily dependent on the extent of intracellular dialysis and not on the holding potential (Vh) or stimulus frequency. When GDP-beta-S was substituted for GTP in the pipette solution, there was no change in the T current or in the rate of run-down of N and L current components. Substitution of GTP-gamma-S for GTP in the pipette solution resulted in a moderate (approximately 40%) loss of isolated T current. This effect was most evident on T currents evoked at relatively positive clamp potentials (Vc, -30 to -15 mV) and occurred relatively late (approximately 10 min) in the recording. In the presence of GTP-gamma-S, currents evoked from Vh = -80 mV, containing the N and L current components, were reduced 40-60%, with a lesser effect on those currents evoked from Vh = -40 mV, containing primarily the L current component. The average time to peak current (Ip) was increased 3-4-fold in the presence of GTP-gamma-S, and the Vc at which the maximal peak current was evoked was shifted +10 to 20 mV. These effects were evident within 2-5 min after initiation of the whole-cell recording. Pretreatment of neurons with pertussis toxin attenuated or blocked the effects of GTP-gamma-S. We conclude that nodose ganglion neurons have T-, N-, and L-type calcium current components, which had different stability during whole-cell recording. Activation of G proteins with GTP-gamma-S reduced N greater than T much greater than L currents, effects reduced in the presence of pertussis toxin. Thus, the calcium current components of nodose ganglion neurons were regulated by cytosolic constituents and by Gi- or Go- type G proteins.
authors.affiliation: Department of Neurology, University of Michigan Medical Center 48104.
authors.forename: R A
authors.initials: RA
authors.lastname: Gross
authors.forename: J W
authors.initials: JW
authors.lastname: Wiley
authors.forename: T
authors.initials: T
authors.lastname: Ryan-Jastrow
authors.forename: R L
authors.initials: RL
authors.lastname: Macdonald
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D009620:Nodose Ganglion / Q000187:drug effects*; D037342:Pertussis Toxin; D051381:Rats; D014630:Vagus Nerve / Q000187:drug effects*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin