The involvement of protein kinase C in the regulation of choline cotransport in Limulus

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 Elsevier Science Inc. All rights reserved.