title: Mastoparan and Rab3AL peptide potentiation of calcium-independent secretory activity in rat melanotrophs is inhibited by GDPbetaS.
abstract: The whole-cell patch-clamp membrane capacitance measurement was used to monitor secretory activity in rat melanotrophs, while rab3AL, putative effector domain peptides of Rab3 small GTPases (20-30 kDa), were introduced into cytosol. In melanotrophs dialyzed with calcium free solutions membrane capacitance tends to decrease slightly. This decrease is further potentiated with GDPbetaS (500 microM). We found that rab3AL (100 microM) stimulated secretory activity in the absence of calcium. The rab3AL response was qualitatively comparable to the response to mastoparan (1 microM), an activator of certain heterotrimeric GTP-binding proteins. Interestingly, inclusion of GDPbetaS (500 microM) resulted in a blockade of both rab3AL and mastoparan induced responses. We conclude that rab3AL and mastoparan induce calcium-independent stimulation of secretory activity in rat melanotrophs by activation of a downstream heterotrimeric GTP-binding protein.
authors.affiliation: Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, School of Medicine, Ljubljana, Slovenia.
authors.forename: M
authors.initials: M
authors.lastname: Rupnik
authors.forename: G J
authors.initials: GJ
authors.lastname: Law
authors.forename: W T
authors.initials: WT
authors.lastname: Mason
authors.forename: R
authors.initials: R
authors.lastname: Zorec
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D004357:Drug Synergism; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology; D014862:Wasp Venoms / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D013873:Thionucleotides; D014862:Wasp Venoms; C083869:rab3AL peptide; D006153:Guanosine Diphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); C037500:mastoparan; D019204:GTP-Binding Proteins; D002118:Calcium