Study on the possible involvement of protein kinases in the modulation of brain presynaptic sodium channels; comparison with calcium channels.
A possible modulatory role of kinases on voltage sensitive Na+ channels of presynaptic brain nerve endings was investigated by testing the effect of several kinase activators and inhibitors on the elevation of [Nai] induced by veratridine in mouse brain synaptosomes loaded with a selective Na+ indicator dye. Veratridine (20 microM) increases the basal [Nai] level (20 mM) more than twofold. This increase is independent of external Ca2+, but abolished by tetrodotoxin (1 microM). Activation of cAMP dependent protein kinase with forskolin or cAMP analogs, or of protein kinase C with diacylglycerol did not affect the veratridine-induced elevation in [Nai]. Drugs reported to inhibit calmodulin-dependent events, as well as the regulatory domain of protein kinase C, were potent and effective inhibitors of the increase in [Nai] induced by veratridine, as well as other veratridine induced responses, namely elevation of [Cai] (monitored with the Ca2+ indicator dye fura-2) and neurotransmitter (GABA) release. Drugs that inhibit kinases by binding to the catalytic site were ineffective, however, as was the phosphatase inhibitor, okadaic acid. A selective inhibitor of Ca2+ and calmodulin dependent protein kinase II also did not affect the elevation of [Nai] induced by veratridine, but markedly diminished the elevation of [Cai] induced by depolarization either with veratridine or with high K+ (15 and 30 mM). On the basis of these results it is concluded that, the dramatic inhibition exerted by some of the drugs tested on the elevation of [Nai] induced by veratridine is not due to their effects on kinases, but to a possible interaction of these compounds with an intracellular site of the Na+ channel. On the other hand, while Ca2+ and calmodulin dependent protein kinase II is unable to modulate brain presynaptic voltage sensitive Na+ channels, it facilitates the activation of brain presynaptic voltage sensitive Ca2+ channels.
Sitges
M
M
Depto. de Biología Celular, Instituto de Investigaciones Biomédicas, México, México. sitges@servidor.unam.mx
Peña
F
F
Chiu
L M
LM
Guarneros
A
A
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D047428:Protein Kinase Inhibitors; D015222:Sodium Channels; D019319:Okadaic Acid; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C063302:KN 62; D014701:Veratridine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D012964:Sodium; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium