An extracellular sulfhydryl group modulates background Na(+) conductance and cytosolic Ca(2+) in pituitary cells.
Treatment of GH(3) pituitary cells with p-chloromercurybenzenesulfonate (PCMBS) increased the cytosolic Ca(2+) concentration ([Ca(2+)](i)). This effect was reversed by dithiothreitol and blocked by L-type Ca(2+) channel antagonists or Na(+) removal. PCMBS increased membrane conductance and depolarized the plasma membrane. Apart from minor effects on K(+) and Ca(2+) channels, PCMBS increased (6 times at -80 mV) an inward Na(+) current whose properties were similar to those of a background Na(+) conductance (BNC) described previously, necessary for generation of spontaneous electrical activity. In rat lactotropes and somatotropes in primary culture, PCMBS also produced a Na(+)-dependent [Ca(2+)](i) increase, whereas little or no effect was observed in thyrotropes, corticotropes, and gonadotropes. The Na(+) conductance elicited by PCMBS in somatotropes seemed to be the same as that stimulated by the hypothalamic growth hormone (GH)-releasing hormone, which regulates membrane excitability and GH secretion. The BNC studied here could play a physiological role, regulating excitability and spontaneous activity, and explains satisfactorily the [Ca(2+)](i)-increasing actions of the mercurials reported previously in several excitable tissues.
Fonteriz
Rosalba I
RI
Instituto de Biología y Genética Molecular, Universidad de Valladolid y Consejo Superior Investigaciones Científicas, Departamento de Fisiología y Bioquímica, Facultad de Medicina, 47005 Valladolid, Spain.
Villalobos
Carlos
C
García-Sancho
Javier
J
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology*
D013439:Sulfhydryl Reagents; D002731:4-Chloromercuribenzenesulfonate; D013007:Growth Hormone-Releasing Hormone; D012964:Sodium; D011188:Potassium; D002118:Calcium