TY - JOUR
T1 - Expression of the extraneuronal monoamine transporter in RPE and neural retina
AU - Rajan, Prasanna D.
AU - Kekuda, Ramesh
AU - Chancy, Christy D.
AU - Huang, Wei
AU - Ganapathy, Vadivel
AU - Smith, Sylvia B
N1 - Funding Information:
This work was supported by National Institutes of Health Grants DA10045 and EY 09682, Fight for Sight Award GA99037, Medical College of Georgia Research Institute, and an unrestricted grant from Research to Prevent Blindness Inc. NY to the Department of Ophthalmology, Medical College of Georgia. We thank Ms. Sue Johnson for assistance in the preparation of the manuscript and Ms. Penny Roon for preparation of the frozen tissue for in situ hybridization. We thank Dr. Ruth Caldwell for the gift of the ARPE-19 cells.
PY - 2000/3
Y1 - 2000/3
N2 - Purpose. Dopamine has several important functions in the retina including a possible role in controlling photoreceptor disk shedding to the RPE. While some cells express a transporter for dopamine, the RPE cell does not, leading us to ask whether the newly described catecholamine transport system, the extraneuronal monoamine transporter (uptake2) (also known as organic cation transporter 3 (OCT3), is present in RPE and might function as a transporter for dopamine. OCT3 also accepts histamine as a transportable substrate and so we investigated the interaction of this retinal neurotransmitter with OCT3. Methods. OCT3 expression in the mouse eye was analyzed by in situ hybridization, Northern blot analysis and RT-PCR. OCT3 function was analyzed in cultured human ARPE-19 cells by monitoring the uptake of 1-methyl-4-phenyl pyridinium (MPP+), a neurotoxin, which is a known substrate for OCT3. Results. In situ hybridization analysis showed that OCT3 is expressed in mouse RPE and in several cell types of the neural retina, including photoreceptor, ganglion, amacrine, and horizontal cells. The expression of OCT3 in RPE was confirmed by Northern blot analysis and RT-PCR. The characteristics of MPP+ uptake in cultured ARPE-19 cells included the stimulation of transport by alkaline pH, high affinity (K(t) = 28 ± 4 μM), competition with several cationic drugs and monoamine neurotransmitters and sensitivity to steroids. In addition, the uptake of MPP+ in RPE cells was inhibited by dopamine and histamine with IC50 values (concentration needed for 50% inhibition) of 637 ± 84 μM and 150 ± 20 μM, respectively. Conclusions. This study provides the first report on the expression and function of an organic cation transporter, OCT3, in the eye and in particular the RPE. The data have physiological and pharmacological relevance as it is likely that OCT3 participates in the clearance of dopamine and histamine from the subretinal space and may also play a key role in the disposition of the retinal neurotoxin MPP+.
AB - Purpose. Dopamine has several important functions in the retina including a possible role in controlling photoreceptor disk shedding to the RPE. While some cells express a transporter for dopamine, the RPE cell does not, leading us to ask whether the newly described catecholamine transport system, the extraneuronal monoamine transporter (uptake2) (also known as organic cation transporter 3 (OCT3), is present in RPE and might function as a transporter for dopamine. OCT3 also accepts histamine as a transportable substrate and so we investigated the interaction of this retinal neurotransmitter with OCT3. Methods. OCT3 expression in the mouse eye was analyzed by in situ hybridization, Northern blot analysis and RT-PCR. OCT3 function was analyzed in cultured human ARPE-19 cells by monitoring the uptake of 1-methyl-4-phenyl pyridinium (MPP+), a neurotoxin, which is a known substrate for OCT3. Results. In situ hybridization analysis showed that OCT3 is expressed in mouse RPE and in several cell types of the neural retina, including photoreceptor, ganglion, amacrine, and horizontal cells. The expression of OCT3 in RPE was confirmed by Northern blot analysis and RT-PCR. The characteristics of MPP+ uptake in cultured ARPE-19 cells included the stimulation of transport by alkaline pH, high affinity (K(t) = 28 ± 4 μM), competition with several cationic drugs and monoamine neurotransmitters and sensitivity to steroids. In addition, the uptake of MPP+ in RPE cells was inhibited by dopamine and histamine with IC50 values (concentration needed for 50% inhibition) of 637 ± 84 μM and 150 ± 20 μM, respectively. Conclusions. This study provides the first report on the expression and function of an organic cation transporter, OCT3, in the eye and in particular the RPE. The data have physiological and pharmacological relevance as it is likely that OCT3 participates in the clearance of dopamine and histamine from the subretinal space and may also play a key role in the disposition of the retinal neurotoxin MPP+.
KW - 1-Methyl-4-phenylpyridinium
KW - Dopamine
KW - Extraneuronal monoamine transporter
KW - Histamine
KW - Organic cation transporter
KW - Retinal pigment epithelium
UR - http://www.scopus.com/inward/record.url?scp=0034087276&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034087276&partnerID=8YFLogxK
U2 - 10.1076/0271-3683(200003)2031-9FT195
DO - 10.1076/0271-3683(200003)2031-9FT195
M3 - Article
C2 - 10694895
AN - SCOPUS:0034087276
SN - 0271-3683
VL - 20
SP - 195
EP - 204
JO - Current Eye Research
JF - Current Eye Research
IS - 3
ER -