Gi-3 protein mediates the increase in voltage-gated K+ currents by somatostatin on cultured ovine somatotrophs.
Voltage-gated K+ currents in rat somatotrophs are increased by somatostatin (SRIF) through unidentified G protein. In this experiment, somatotroph-enriched cells (up to 85%) were obtained from ovine pituitary glands and further identified by the increase in K+ currents by SRIF. The whole cell recording was employed to study the voltage-gated K+ currents. A reversible increase in K+ currents (up to 150% of control) was obtained in response to local application of SRIF (10 nM) but not vehicle. When the guanosine 5'-O-(3-thiotriphosphate) was included in the pipette solution (200 microM), the recovery phase of K+ current response to SRIF was abolished. Inclusion of guanosine 5'-O-(2-thiodiphosphate) (200 microM) in pipette solution blocked the K+ current response to SRIF. Intracellular dialysis of antibodies against alphao-, alphai-, alphai-1-2-, or alphai-3-subunits of G proteins via patch pipettes was confirmed by immunofluorescent staining of the antibodies. Antibody dialysis alone did not modify voltage-gated K+ currents. Dialysis of anti-alphai or anti-alphai-3 antibodies significantly attenuated the increase in K+ currents that was obtained after application of 10 or 100 nM SRIF. Dialysis with anti-alphao, anti-alphai-1-2, or heat-inactivated (60 degreesC for 10 min) anti-alphai antibodies did not diminish the effect of SRIF on K+ currents. We conclude that the Gi-3 protein mediates the effect of SRIF on voltage-gated K+ currents in ovine somatotrophs.
Chen
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Prince Henry's Institute of Medical Research, Clayton, Victoria 3168, Australia.
D000818:Animals; D000906:Antibodies; D002478:Cells, Cultured; D005071:Evoked Potentials / Q000187:drug effects; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007150:Immunohistochemistry; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012756:Sheep; D013004:Somatostatin / Q000494:pharmacology* / Q000502:physiology; D013997:Time Factors
D000906:Antibodies; D015221:Potassium Channels; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013004:Somatostatin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go