Inhibition of the L-type calcium channel by the five muscarinic receptors (m1-m5) expressed in NIH 3T3 cells.
Modulation of L-type calcium channels by the five cloned muscarinic receptors was studied by expression of the receptors in NIH 3T3 cells. Application of acetylcholine (ACh) to cells transfected with m1-m5 resulted in a reduction in the L-type calcium current amplitude. Elevations in intracellular cAMP concentrations induced by 8-bromo-cAMP or forskolin resulted in no discernible change in the L-type calcium current. In addition, treatment with Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPS), a protein kinase A (PKA) inhibitor, had no effect on the L-type currents. Conversely, application of phorbol dibutyrate, an activator of protein kinase C (PKC) or 8-bromo-cGMP, an activator of cGMP-dependent protein kinase (PKG), reduced the calcium currents. Incubation of the cells with KT5823, an inhibitor of PKG, resulted in a reduction of the response to 8-bromo-cGMP. The ACh-induced depression of L-type calcium current amplitude was sensitive to pertussis toxin (PTX) in cells transfected with the m2 or m4 receptor subtype. The m2-muscarinic-receptor-induced inhibition of the L-type calcium current was attenuated by preincubation of the cells with 8-bromo-cAMP and was unaffected by KT5823 or by calphostin C. The m1-muscarinic-receptor-induced inhibition of the L-type calcium conductance was insensitive to PTX treatment. However, the m1-induced response was blocked by preincubation of the cells with calphostin C. The present data indicate that the m2 (and possibly also the m4) muscarinic receptors inhibit the L-type calcium conductance by a reduction in cAMP concentration and that the m1 (and possibly also the m3 and m5) muscarinic receptors inhibit the L-type calcium channel via activation of PKC.
Pemberton
K E
KE
Molecular Neuropharmacology, Departments of Psychiatry, Pharmacology and Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington VT 05405, USA.
Jones
S V
SV
D016475:3T3 Cells / Q000187:drug effects*; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000502:physiology*
D015220:Calcium Channels; D011976:Receptors, Muscarinic; D009543:Nifedipine