Differential regulation of mammalian brain-specific proline transporter bycalcium and calcium-dependent protein kinases

1 This study examined the role of [Ca2+](I) and Ca2+-dependent kinases in t he modulation of high-affinity, mammalian brain-specific L-proline transpor ter (PROT). 2 beta-PMA (phorbol 12-myristate 13-acetate), an activator of protein kinas e C (PKC), inhibits PRO uptake, and bisindolylmalemide I (BIM), a potent PK C inhibitor, prevents beta-PMA inhibition. Down-regulation of PKC by chroni c treatment with beta-PMA enhances PROT function indicating PROT regulation by tonic activity of PKC. 3 Thapsigargin, which increases [Ca2+](I) levels by inhibiting Ca2+-ATPase, inhibits PROT and exhibits additive inhibition when co-treated with beta-P MA. KN-62, a Ca2+/calmodulin-dependent kinase II (CaMK II) inhibitor, but n ot BIM (a PKC inhibitor) prevents the inhibition by thapsigargin. These dat a suggest that PKC and CaMK II modulate PROT and that thapsigargin mediates its effect via CaMK II. 4 Thapsigargin raises [Ca2+](I) and increases PRO-induced current on a seco nd time scale, whereas the inhibitory effect of thapsigargin occurs only af ter 10 min of treatment. These data suggest that Ca2+ differentially regula te PROT: Ca2+ initially enhances PRO transport but eventually inhibits tran sport function through CaMK II pathway. 5 Ca2+-induced stimulation exemplifies the acute regulation of a neurotrans mitter transporter, which may play a critical role in the profile of neurot ransmitters during synaptic transmission.