Rat group I metabotropic glutamate receptors inhibit neuronal Ca2+ channels via multiple signal transduction pathways in HEK 293 cells.
We have shown previously that metabotropic glutamate receptors with group I-like pharmacology couple to N-type and P/Q-type calcium channels in acutely isolated cortical neurons using G proteins most likely belonging to the Gi/Go subclass. To better understand the potential mechanisms forming the basis for group I mGluR modulation of voltage-gated calcium channels in the CNS, we have examined the ability of specific mGluRs to couple to neuronal N-type (alpha1B-1/alpha2delta/beta1b) and P/Q-type (alpha1A-2/alpha2delta/beta1b) voltage-gated calcium channels in an HEK 293 heterologous expression system. Using the whole cell patch-clamp technique where intracellular calcium is buffered to low levels, we have shown that group I receptors inhibit both N-type and P/Q-type calcium channels in a voltage-dependent fashion. Similar to our observations in cortical neurons, this voltage-dependent inhibition is mediated almost entirely by N-ethylmaleimide (NEM)-sensitive heterotrimeric G proteins, strongly suggesting that these receptors can use Gi/Go-like G proteins to couple to N-type and P/Q-type calcium channels. However, inconsistent with the apparent NEM sensitivity of group I modulation of calcium channels, modulation of N-type channels in group I mGluR-expressing cells was only partially sensitive to pertussis toxin (PTX), indicating the potential involvement of both PTX-sensitive and -resistant G proteins. The PTX-resistant modulation was voltage dependent and entirely resistant to NEM and cholera toxin. A time course of treatment with PTX revealed that this toxin caused group I receptors to slowly shift from using a primarily NEM-sensitive G protein to using a NEM-resistant form. The PTX-induced switch from NEM-sensitive to -resistant modulation was also dependent on protein synthesis, indicating some reliance on active cellular processes. In addition to these voltage-dependent pathways, perforated patch recordings on group I mGluR-expressing cells indicate that another slowly developing, calcium-dependent form of modulation for N-type channels may be seen when intracellular calcium is not highly buffered. We conclude that group I mGluRs can modulate neuronal Ca2+ channels using a variety of signal transduction pathways and propose that the relative contributions of different pathways may exemplify the diversity of responses mediated by these receptors in the CNS.
McCool
B A
BA
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37203, USA.
Pin
J P
JP
Harpold
M M
MM
Brust
P F
PF
Stauderman
K A
KA
Lovinger
D M
DM
D000818:Animals; D000068438:Brimonidine Tartrate; D015220:Calcium Channels / Q000096:biosynthesis / Q000502:physiology*; D020864:Calcium Channels, N-Type; D002460:Cell Line; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D018698:Glutamic Acid / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D037342:Pertussis Toxin; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000096:biosynthesis; D015398:Signal Transduction; D017783:Superior Cervical Ganglion / Q000502:physiology*; D014162:Transfection; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000068438:Brimonidine Tartrate; D015220:Calcium Channels; D020864:Calcium Channels, N-Type; D019204:GTP-Binding Proteins; D018698:Glutamic Acid; D037342:Pertussis Toxin; D011810:Quinoxalines; D018094:Receptors, Metabotropic Glutamate; D011994:Recombinant Proteins; D014660:Vasoactive Intestinal Peptide; D010566:Virulence Factors, Bordetella