title: Modulation by BNP of GABA receptors on ON-type rod bipolar cells is dependent on subcellular sites.
abstract: Brain natriuretic peptide (BNP) suppresses GABA(A) receptor-mediated current of ON-type rod-dominant bipolar cells (RBCs) in the rat retina. Here we report that such BNP-induced modulation is dependent on subcellular sites. Whole-cell currents could be induced by GABA focally applied to both dendrites/somata and axon terminals of isolated ON-type RBCs. Whilst the GABA currents induced at the axon terminal were significantly suppressed by BNP (50 nM), those at the dendrites/somata were hardly changed or slightly suppressed. Similar results were obtained when such experiments were performed in rat retinal slices. Calcium imaging showed that application of BNP (50 nM) caused a prominent increase in intracellular calcium concentrations ([Ca(2+)](i)) at the axon terminal, and the increase monotonically decayed when the acting site of BNP was moved away from the axon terminal along the cell: more distant, less significant. No detectable increase in [Ca(2+)](i) was found at the dendrites. Such increase in [Ca(2+)](i) could be completely blocked by pre-incubation with anantin, an antagonist of the NP-receptor-A (NPR-A). On the other hand, caffeine, an agonist of the ryanodine receptor, caused a similar subcellular site-dependent changes in [Ca(2+)](i), thus mimicking the BNP effect. All these results suggest that BNP-induced modulation of the activity of GABA receptors may be largely restricted to the inner retina.
authors.affiliation: Institute of Neurobiology, Institutes of Brain Science and State Key Laboratory of Medical Neurobiology, Fudan University, 138 Yixueyuan Road, Shanghai 200032, China.
authors.forename: Li-Hui
authors.initials: LH
authors.lastname: Cao
authors.forename: Bo
authors.initials: B
authors.lastname: Zhou
authors.forename: Xiong-Li
authors.initials: XL
authors.lastname: Yang
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D066298:In Vitro Techniques; D020097:Natriuretic Peptide, Brain / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018079:Receptors, GABA / Q000378:metabolism*; D051245:Retinal Bipolar Cells / Q000145:classification / Q000166:cytology / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000378:metabolism*
chemical_list: D018079:Receptors, GABA; D020097:Natriuretic Peptide, Brain; D002118:Calcium