Modulation of neuronal T-type calcium channel currents by photoactivation of intracellular guanosine 5'-O(3-thio) triphosphate

Neuroscience. 1990;38(2):285-94. doi: 10.1016/0306-4522(90)90028-3.


Low voltage-activated T-type Ca2+ channel currents were recorded from cultured rat dorsal root ganglion neurons using the whole-cell clamp technique with Ba2+ as the charge carrier. The T-type Ca2+ channel current was identified by its low threshold of activation (Vc -50 to -20 mV from VH - 90 mV), its kinetics of inactivation and its sensitivity to NiCl2 (100 microM). It was also sensitive to 1-octanol (1 microM). omega-Conotoxin (1 microM) markedly reduced the high threshold voltage-activated Ca2+ channel currents but did not inhibit the T-type Ca2+ channel current. Photorelease of intracellular guanosine 5'-O(3-thio) triphosphate from a photolabile "caged" precursor had dose-dependent effects on the T-type Ca2+ channel current. At a concentration of 6 microM, guanosine 5'-O(3-thio) triphosphate enhanced the current, but further photorelease of guanosine 5'-O(3-thio) triphosphate (up to 20 microM) inhibited the current. Only the inhibitory response was sensitive to pertussis toxin. These data suggest that more than one G-protein is involved in T-type Ca2+ channel current modulation. Inclusion of guanosine 5'-O(2-thio) diphosphate (1 mM) in the patch solution prevented guanosine 5'-O(3-thio) triphosphate from potentiating the current, and greatly attenuated the inhibitory effects observed when larger amounts of guanosine 5'-O(3-thio) triphosphate were photoreleased. Photorelease of guanosine 5'-O(2-thio) diphosphate had no effect on T-type current but did significantly increase the high voltage-activated current. A low concentration of (-)-baclofen (2 microM), potentiated T-type current, while 100 microM(-)-baclofen inhibited T-type current.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Baclofen / pharmacology
  • Calcium Channels / physiology*
  • Calcium Channels / radiation effects
  • Culture Techniques
  • Electrophysiology
  • Ganglia, Spinal / cytology
  • Ganglia, Spinal / metabolism
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Guanosine 5'-O-(3-Thiotriphosphate) / physiology*
  • Intracellular Membranes / metabolism*
  • Light*
  • Neurons / metabolism*
  • Rats
  • Rats, Inbred Strains
  • Stereoisomerism


  • Calcium Channels
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Baclofen