Modulatory Effect On Voltage Gated Calcium Channel Expressed On Carp Horizontal Cell By Dopamine

Dopamine (DA) regulates the neuronal activity by intracellular secondmessenger system, as a neuromodulator or neurohormone in central nervoussystem (CNS). DA released from dopaminergic neuron in retina regulatesactivity of calcium channel on horizontal cell by activating dopaminereceptor via synapses or diffuse release. Voltage gated calcium channel(VGCC) is one of the main calcium ion influx channels mediating calciumion exchange between cytoplasm and extracellular fluid on horizontal cellmembrane. VGCC activity is inhibited in extracelluar acidic environment,while enhanced in extracelluar alkaline environment.The present study examined the modulatory effect of DA (50umol/L,500umol/L,1mmol/L) on L-type VGCC expressed on H1type horizontalcell in different pH conditions using intracellular calcium imaging techniques.The main results showed that in different pH conditions (pH=6.8,7.4,8.0),DA (50μmol/L,500μmol/L,1mmol/L) up-regulated L-VGCC;50μmol/LDA had an up-regulation effect on L-VGCC, without significant difference indifferent pH conditions; in different pH conditions, high concentration DA(500μmol/L,1mmol/L) up-regulated L-VGCC differentially, with greater regulation in pH=8.0than pH=6.8or7.4, without significant differencebetween pH=6.8and7.4conditions. These results suggest that themodulatory effect of DA on L-VGCC is related to extracellular pH. In light,extracelluar environment is alkaline and DA release is enhanced in retina. Soin retinal light response, L-VGCC is up-regulated by relatively highconcentration DA with collaborative enhancement of extracellularalkalization, enhancing the calcium signal.