Nicotinamide-adenine dinucleotide regulates muscarinic receptor-coupled K+ (M) channels in rodent NG108-15 cells.
1. The possible role of nicotinamide-adenine dinucleotide (NAD+) and cyclic adenosine diphosphate ribose (cADPR) as regulators of M-type K+ currents (IK(M)) has been studied in whole-cell patch-clamped NG108-15 mouse neuroblastoma x rat glioma cells that had been transformed to express m1 muscarinic acetylcholine receptors (mAChRs). 2. Pre-incubation of NG108-15 cells for 6-8 h with streptozotocin (2-5 mM) reduced NAD+ levels by 40-50%. Nicotinamide (2-5 mM) increased NAD+ levels and prevented depletion by streptozotocin. 3. Streptozotocin pretreatment reduced the inhibition of IK(M) produced by 100 microM acetylcholine (ACh) from 51.6 +/- 7.0 to 29.1 +/- 7.5%. This was prevented by simultaneous pre-incubation with 2 mM nicotinamide or by adding 2 mM NAD+ to the pipette solution. Neither procedure significantly affected the initial amplitude of IK(M). 4. Inclusion of 2 microM cADPR in the pipette solution induced a slow loss of IK(M) with a time constant of about 20 min. 5. It is concluded that mAChR-induced inhibition of IK(M) requires intracellular NAD+. This might be needed for the formation of cADPR as a regulator or messenger for IK(M) inhibition.
Higashida
H
H
Department of Biophysics, Kanazawa University School of Medicine, Japan.
Robbins
J
J
Egorova
A
A
Noda
M
M
Taketo
M
M
Ishizaka
N
N
Takasawa
S
S
Okamoto
H
H
Brown
D A
DA
D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000502:physiology; D000818:Animals; D036563:Cyclic ADP-Ribose; D051379:Mice; D009243:NAD / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000502:physiology*; D013311:Streptozocin / Q000494:pharmacology; D013552:Swine; D014407:Tumor Cells, Cultured
D015221:Potassium Channels; D011976:Receptors, Muscarinic; D009243:NAD; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D013311:Streptozocin