TY - JOUR
T1 - Lobeline displaces [3H] dihydrotetrabenazine binding and releases [3H]dopamine from rat striatal synaptic vesicles
T2 - Comparison with d- amphetamine
AU - Teng, Li Hong
AU - Crooks, Peter A.
AU - Dwoskin, Linda P.
PY - 1998/7
Y1 - 1998/7
N2 - Lobeline, an alkaloid from Indian tobacco (Lobella inflata), is classified as a nicotinic agonist and is currently used as a smoking cessation agent. However, our previous in vitro studies demonstrate that lobeline does not act as a nicotinic agonist but alters presynaptic dopamine (DA) storage by potently inhibiting DA uptake into synaptic vesicles. Recently, d-amphetamine has been reported to act at the level of the synaptic vesicle to alter presynaptic function. The present in vitro studies further elucidate the mechanism of lobeline's action and compare its effects with those of d-amphetamine. [3H]Dihydrotetrabenazine ([3H ] DTBZ), used routinely to probe a high-affinity binding site on the vesicular monoamine transporter (VMAT2), bound to vesicle membranes from rat striatum with a K(D) of 1.67 nM and B(max) of 8.68 pmol/mg of protein. Lobeline inhibited [3H]DTBZ binding with an IC50 of 0.90 μM, consistent with its previously reported IC50 of 0.88 μM for inhibition of [3H]DA uptake into vesicles. These results suggest that lobeline specifically interacts with DTBZ sites on VMAT2 to inhibit DA uptake into synaptic vesicles. Interestingly, d- amphetamine inhibited [3H]DTBz binding to vesicle membranes with an IC50 of 39.4 μM, a concentration 20 times greater than reported for inhibition of VMAT2 function, suggesting that d-amphetamine interacts with a different site than lobeline on VMAT2 to inhibit monoamine uptake. Kinetic analysis of [all] DA release from [3H] DA-preloaded synaptic vesicles in the absence of drug revealed a t(1/2) of 2.12 min. Lobeline and d-amphetamine evoked [3H]DA release with EC50 values of 25.3 and 2.22 μM, respectively. At a concentration 10 times the EC50, lobeline and d-amphetamine significantly decreased the t(1/2) of [3H]DA release to 1.58 and 1.48 min, respectively. Thus, in contrast to d-amphetamine, which is equipotent in inhibiting DA uptake and promoting release from the synaptic vesicles, lobeline more potently (28-fold) inhibits DA uptake (via an interaction with the DTBZ site on VMAT2) than it evokes DA release to redistribute presynaptic DA storage.
AB - Lobeline, an alkaloid from Indian tobacco (Lobella inflata), is classified as a nicotinic agonist and is currently used as a smoking cessation agent. However, our previous in vitro studies demonstrate that lobeline does not act as a nicotinic agonist but alters presynaptic dopamine (DA) storage by potently inhibiting DA uptake into synaptic vesicles. Recently, d-amphetamine has been reported to act at the level of the synaptic vesicle to alter presynaptic function. The present in vitro studies further elucidate the mechanism of lobeline's action and compare its effects with those of d-amphetamine. [3H]Dihydrotetrabenazine ([3H ] DTBZ), used routinely to probe a high-affinity binding site on the vesicular monoamine transporter (VMAT2), bound to vesicle membranes from rat striatum with a K(D) of 1.67 nM and B(max) of 8.68 pmol/mg of protein. Lobeline inhibited [3H]DTBZ binding with an IC50 of 0.90 μM, consistent with its previously reported IC50 of 0.88 μM for inhibition of [3H]DA uptake into vesicles. These results suggest that lobeline specifically interacts with DTBZ sites on VMAT2 to inhibit DA uptake into synaptic vesicles. Interestingly, d- amphetamine inhibited [3H]DTBz binding to vesicle membranes with an IC50 of 39.4 μM, a concentration 20 times greater than reported for inhibition of VMAT2 function, suggesting that d-amphetamine interacts with a different site than lobeline on VMAT2 to inhibit monoamine uptake. Kinetic analysis of [all] DA release from [3H] DA-preloaded synaptic vesicles in the absence of drug revealed a t(1/2) of 2.12 min. Lobeline and d-amphetamine evoked [3H]DA release with EC50 values of 25.3 and 2.22 μM, respectively. At a concentration 10 times the EC50, lobeline and d-amphetamine significantly decreased the t(1/2) of [3H]DA release to 1.58 and 1.48 min, respectively. Thus, in contrast to d-amphetamine, which is equipotent in inhibiting DA uptake and promoting release from the synaptic vesicles, lobeline more potently (28-fold) inhibits DA uptake (via an interaction with the DTBZ site on VMAT2) than it evokes DA release to redistribute presynaptic DA storage.
KW - Dihydrotetrabenazine
KW - Dopamine
KW - Lobeline
KW - Vesicular monoamine transporter
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U2 - 10.1046/j.1471-4159.1998.71010258.x
DO - 10.1046/j.1471-4159.1998.71010258.x
M3 - Article
C2 - 9648873
AN - SCOPUS:0031595598
SN - 0022-3042
VL - 71
SP - 258
EP - 265
JO - Journal of Neurochemistry
JF - Journal of Neurochemistry
IS - 1
ER -