The involvement of protein kinase C (PKC) in the regulation of [H-3]choline
cotransport was studied in Limulus brain hemi-slice preparations. The PKC
activators, phorbol 12-myristate 13-acetate (PMA) or phorbol 12,13-dibutyra
te (PDBu), significantly decreased [H-3]choline cotransport. Conversely, th
e PKC inhibitors, staurosporine (STAURO) and polymyxin B (PMB), each increa
sed [H-3]choline cotransport. These PKC inhibitors prevented the phorbol es
ter-induced reduction of transport. Both the PMA induced decrease and the S
TAURO induced increase in [H-3]choline cotransport were paralleled by respe
ctive and comparable changes in [H-3]hemicholinium-3 (HC-3) specific bindin
g. Pre-exposure of brain hemi-slices to elevated potassium chloride (120 mM
KCl) resulted in a doubling of [H-3]choline cotransport and [H-3]HC-3 bind
ing. The enhancement of [H-3]choline cotransport by STAURO and antecedent 1
20 mM KCl treatment were additive. PMA did not significantly alter elevated
potassium stimulated transport. Moreover, arachidonyltrifluoromethyl keton
e (AACOCF(3)) and quinacrine (QUIN), both phospholipase A(2) (PLA(2)) inhib
itors, markedly decreased enhanced [H-3]choline transport and [H-3]HC-3 bin
ding induced by antecedent exposure to depolarizing concentrations of potas
sium. These results suggest that PKC and PLA(2) are involved in the regulat
ion of [H-3]choline cotransport but at different regulatory sites. (C) 1999
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