Recovery from desensitization of neuronal nicotinic acetylcholine receptors of rat chromaffin cells is modulated by intracellular calcium through distinct second messengers.
The mechanisms through which changes in intracellular Ca2+ concentration ([Ca2+]i) might influence desensitization of neuronal nicotinic receptors (nAChRs) of rat chromaffin cells were investigated by simultaneous patch-clamp recording of membrane currents and confocal microscopy imaging of [Ca2+]i induced by nicotine. Increases in [Ca2+]i that were induced by membrane depolarization or occurred spontaneously did not influence inward currents elicited by focally applied test pulses (10 msec) of nicotine, indicating that raised [Ca2+]i per se did not trigger desensitization of nAChRs. Desensitization of nAChRs, evoked by 2 sec focal application of nicotine, which largely raised [Ca2+]i, was not affected by intracellular application of agents that activate or depress protein kinase C (PKC) or A (PKA) or inhibit phosphatase 1, 2 A and B. Conversely, recovery from desensitization was facilitated by the phorbol ester phorbol 12-myristate 13-acetate (PMA) or the phosphatase 2 B inhibiting complex of cyclosporin A-cyclophilin A, whereas it was impaired by the broad spectrum kinase inhibitor staurosporine. The effects of PMA or staurosporine were prevented by the intracellularly applied Ca2+ chelator BAPTA. The adenylate cyclase activator forskolin accelerated recovery, whereas the selective PKA antagonist Rp-cAMPS had an opposite effect. The action of staurosporine and Rp-cAMPS on recovery from desensitization was additive. It is proposed that when nAChRs are desensitized, they become susceptible to modulation by [Ca2+]i via intracellular second messengers such as serine/threonine kinases and calcineurin. Thus, the phosphorylation state of neuronal nAChRs appears to regulate their rate of recovery from desensitization.
Khiroug
L
L
Biophysics Sector and Istituto Nazionale di Fisica della Materia Unit, International School for Advanced Studies (SISSA), 34013 Trieste, Italy.
Sokolova
E
E
Giniatullin
R
R
Afzalov
R
R
Nistri
A
A
D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology; D019439:Chromaffin Cells / Q000737:chemistry* / Q000201:enzymology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D016716:PC12 Cells; D018408:Patch-Clamp Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D051381:Rats; D011978:Receptors, Nicotinic / Q000502:physiology*; D015290:Second Messenger Systems / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D002273:Carcinogens; D004791:Enzyme Inhibitors; D018722:Nicotinic Agonists; D010703:Phorbol Esters; D011978:Receptors, Nicotinic; D013873:Thionucleotides; D005576:Colforsin; C016957:adenosine-3',5'-cyclic phosphorothioate; D009538:Nicotine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D019311:Staurosporine; D002118:Calcium