Muscarinic M(1) modulation of N and L types of calcium channels is mediated by protein kinase C in neostriatal neurons.
In some neurons, muscarinic M(1)-class receptors control L-type (Ca(V)1) Ca(2+)-channels via protein kinase C (PKC) or calcineurin (phosphatase 2B; PP-2B) signaling pathways. Both PKC and PP-2B pathways start with phospholipase C (PLC) activation. In contrast, P/Q- and N-type (Ca(V)2.1, 2.2, respectively) Ca(2+)-channels are controlled by M(2)-class receptors via G proteins that may act, directly, to modulate these channels. The hypothesis of this work is that this description is not enough to explain muscarinic modulation of Ca(2+) channels in rat neostriatal projection neurons. Thus, we took advantage of the specific muscarinic toxin 3 (MT-3) to block M(4)-type receptors in neostriatal neurons, and leave in isolation the M(1)-type receptors to study them separately. We then asked what Ca(2+) channels are modulated by M(1)-type receptors only. We found that M(1)-receptors do modulate L, N and P/Q-types Ca(2+) channels. This modulation is blocked by the M(1)-class receptor antagonist (muscarinic toxin 7, MT-7) and is voltage-independent. Thereafter, we asked what signaling pathways, activated by M(1)-receptors would control these channels. We found that inactivation of PLC abolishes the modulation of all three channel types. PKC activators (phorbol esters) mimic muscarinic actions, whereas reduction of intracellular calcium virtually abolishes all modulation. As expected, PKC inhibitors prevented the muscarinic reduction of the afterhyperpolarizing potential (AHP), an event known to be dependent on Ca(2+) entry via N- and P/Q-type Ca(2+) channels. However, PKC inhibitors (bisindolylmaleimide I and PKC-1936) only block modulation of currents through N and L types Ca(2+) channels; while the modulation of P/Q-type Ca(2+) channels remains unaffected. These results show that different branches of the same signaling cascade can be used to modulate different Ca(2+) channels. Finally, we found no evidence of calcineurin modulating these Ca(2+) channels during M(1)-receptor activation, although, in the same cells, we demonstrate functional PP-2B by activating dopaminergic D(2)-receptor modulation.
Perez-Burgos
A
A
Departamento de Biofísica, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City DF, Mexico 04510.
Perez-Rosello
T
T
Salgado
H
H
Flores-Barrera
E
E
Prieto
G A
GA
Figueroa
A
A
Galarraga
E
E
Bargas
J
J
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020864:Calcium Channels, N-Type / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004546:Elapid Venoms / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009116:Muscarine / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D017072:Neostriatum / Q000166:cytology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D043643:Receptor, Muscarinic M1 / Q000037:antagonists & inhibitors / Q000502:physiology*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D004546:Elapid Venoms; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D004963:Estrenes; D018727:Muscarinic Antagonists; D010703:Phorbol Esters; D011760:Pyrrolidinones; D043643:Receptor, Muscarinic M1; C419876:muscarinic toxin 7; C074854:U 73343; D009116:Muscarine; D011493:Protein Kinase C