Dependence of intracellular effects of GTP gamma S and inositoltrisphosphate on cell membrane potential and on external Ca ions.
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.
Llano
I
I
Marty
A
A
Tanguy
J
J
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D005088:Exocrine Glands / Q000187:drug effects / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007700:Kinetics; D007765:Lacrimal Apparatus / Q000187:drug effects / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D013403:Sugar Phosphates / Q000494:pharmacology*; D013873:Thionucleotides / Q000494:pharmacology*
D002413:Cations, Divalent; D007295:Inositol Phosphates; D013403:Sugar Phosphates; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D008274:Magnesium; D002118:Calcium