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Inhibition of the omega-conotoxin-sensitive calcium current by distinct G proteins
1Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235.
Abstract:
Leu-enkephalin (Leu-Enk), norepinephrine (NE), somatostatin (SS), and bradykinin (BK) decrease the voltage-dependent calcium current in NG108-15 cells. Here we have investigated whether distinct G proteins, or a G protein common to all of the pathways, mediates this inhibition. We found that pertussis toxin (PTX) reduced all of these transmitter actions, except that of BK. To examine which of the PTX-sensitive pathways is transduced by GoA, we constructed an NG108-15 cell line that stably expresses a mutant, PTX-resistant alpha subunit of GoA. After treatment with PTX, the mutant GoA alpha rescued the Leu-Enk and NE pathways but not the SS pathway. At least three different G proteins can transduce receptor-mediated inhibition of calcium currents in nerve cells. The effects of these G proteins appear to converge on the omega-conotoxin GVIA-sensitive calcium current.
Insights
Different G proteins mediate neurotransmitter inhibition of calcium currents in nerve cells. Pertussis toxin identified distinct pathways, with GoA rescuing Leu-enkephalin and norepinephrine signaling.
Area of Science:
- Neuroscience
- Cellular Biology
- Molecular Pharmacology
Background:
- Neurotransmitters like Leu-enkephalin (Leu-Enk), norepinephrine (NE), somatostatin (SS), and bradykinin (BK) modulate neuronal excitability by inhibiting voltage-dependent calcium currents.
- G proteins are key signal transducers in these inhibitory pathways, but the specific G proteins involved remain incompletely understood.
Purpose of the Study:
- To elucidate the specific G proteins mediating the inhibitory effects of Leu-Enk, NE, SS, and BK on calcium currents in NG108-15 cells.
- To determine if a common or distinct set of G proteins transduces these diverse receptor-mediated signals.
Main Methods:
- Utilized pertussis toxin (PTX) to inactivate specific G proteins and assess its effect on transmitter-induced calcium current inhibition.
- Generated a cell line stably expressing a PTX-resistant mutant alpha subunit of the GoA G protein.
- Investigated the rescue of signaling pathways by the mutant GoA alpha subunit following PTX treatment.
Main Results:
- Pertussis toxin (PTX) inhibited the actions of Leu-Enk, NE, and SS, but not BK, indicating PTX-sensitive and insensitive pathways.
- The PTX-resistant mutant GoA alpha subunit rescued the inhibitory effects of Leu-Enk and NE after PTX treatment.
- The SS pathway was not rescued by the mutant GoA alpha, suggesting involvement of other PTX-sensitive G proteins.
Conclusions:
- At least three distinct G proteins mediate receptor-induced inhibition of calcium currents in nerve cells.
- These distinct G protein pathways converge on the omega-conotoxin GVIA-sensitive calcium current.
- GoA specifically transduces Leu-Enk and NE signaling, while other G proteins mediate SS inhibition.