Dependence of intracellular effects of GTP gamma S and inositoltrisphosphate on cell membrane potential and on external Ca ions

Pflugers Arch. 1987 Aug;409(4-5):499-506. doi: 10.1007/BF00583807.


Single cells from rat lacrimal glands were studied with the tight-seal whole-cell recording method. Ca-dependent K and Cl currents were measured in response to dialysis with inositoltrisphosphate or GTP gamma S, two compounds known for elevating internal Ca2+ concentration. The activation of the Ca-dependent currents elicited by either compound was partially inhibited by sustained depolarization or by removal of external Ca2+. Conversely, hyperpolarization or removal of external Mg2+ led to augmentations of the Ca-dependent currents. These effects became apparent about 1 min after initiation of cell dialysis with inositoltrisphosphate- or GTP gamma S-containing solutions, and they further developed during the ensuing 10 min. Holding potential and external divalent cations did not affect the Ca-dependent currents elicited by dialysing the cells with strongly buffered solutions containing 0.5 microM free Ca2+. In Ca2+-free external saline, cell currents were independent of the holding potential. It is suggested that InsP3 augments intracellular Ca2+ levels not only by releasing Ca2+ from internal stores but also by slowly increasing the Ca permeability of the plasma membrane. The results indicate that Ca2+ entry through the plasma membrane increases with hyperpolarization. The similarity of the effects seen in InsP3- and GTP gamma S-dialysed cells gives support to the hypothesis that production of the former depends on a GTP-binding protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / pharmacology*
  • Cations, Divalent
  • Exocrine Glands / drug effects
  • Exocrine Glands / physiology*
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Guanosine Triphosphate / analogs & derivatives*
  • Guanosine Triphosphate / pharmacology
  • In Vitro Techniques
  • Inositol 1,4,5-Trisphosphate
  • Inositol Phosphates / pharmacology*
  • Kinetics
  • Lacrimal Apparatus / drug effects
  • Lacrimal Apparatus / physiology
  • Magnesium / pharmacology
  • Membrane Potentials / drug effects
  • Rats
  • Sugar Phosphates / pharmacology*
  • Thionucleotides / pharmacology*


  • Cations, Divalent
  • Inositol Phosphates
  • Sugar Phosphates
  • Thionucleotides
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Inositol 1,4,5-Trisphosphate
  • Guanosine Triphosphate
  • Magnesium
  • Calcium