GTP gamma S stimulates exocytosis in patch-clamped rat melanotrophs.
We investigated the molecular mechanisms regulating exocytosis in patch-clamped melanotrophs by measuring the membrane capacitance. Ca(2+)-dependent exocytosis could be induced by membrane depolarization or by including solutions containing 2 microM free Ca2+ in the patch pipette. Ca(2+)-dependent exocytosis was inhibited by GDP beta S, suggesting involvement of a GTP-binding protein. The hydrolysis-resistant GTP analogs, GTP gamma S and GppNHp, were able to stimulate exocytosis at low free Ca2+ concentrations. The stimulatory response to GTP gamma S was abolished by both GDP beta S and GTP. The latter suggests that a sustained activation of a GTP-binding protein is necessary for exocytosis. This behavior is similar to the stimulation of exocytosis by guanine nucleotides in mast cells and other nonexcitable cells and suggests a common regulatory mechanism.
Okano
K
K
Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Monck
J R
JR
Fernandez
J M
JM
D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology / Q000379:methods; D004789:Enzyme Activation; D005089:Exocytosis; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009712:Nucleotides, Cyclic / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology
D002021:Buffers; D009712:Nucleotides, Cyclic; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D006160:Guanosine Triphosphate; D009074:Melanocyte-Stimulating Hormones; D011494:Protein Kinases; D011493:Protein Kinase C; D002118:Calcium