D1– and D2–Like Dopamine Receptor Activity Enhance Outward K+ Currents In Zebrafish Retinal Bipolar Cells

Abstract

Abstract: : Purpose: To determine how dopamine affects depolarization elicited K⁺ currents recorded from bipolar cells in the zebrafish retina slice, and identify whether D1–like, D2–like, or both type of dopamine receptor mediate this response. Methods: Voltage–gated K⁺ currents were recorded using whole–cell patch clamp techniques from zebrafish (Danio rerio) bipolar cells in the in vivo retina slice. Recordings were made using a K–based intracellular solution and a standard Ringers solution containing 5mM cobalt chloride. Dopamine modulation of K⁺ currents was determined by examining current traces following the addition of either dopamine, SKF–23390, quinpirole, SCH–23390, or spiperone to the bath solution. Results: Outward K⁺ currents were enhanced 83% above control levels when 200µM dopamine was present in the recording solution. This enhancement was completely blocked by the D1–like receptor antagonist, SCH–23390 (5µM), and partially blocked by the D2–like receptor antagonist, spiperone (10µM). 25µM SKF–38393, a D1–like receptor agonist, enhanced current amplitude 38%, while 25µM quinpirole, a D2–like receptor agonist, enhanced depolarization elicited voltage–gated K⁺ currents 68% above control levels. Co–application of 25µM SKF–38393 and 25µM quinpirole only enhanced current amplitude 18%. Conclusions: These findings are significant as they show both D1–like and D2–like dopamine receptors are found, and often co–localized on, zebrafish bipolar cells. Furthermore, the reduced current enhancement following co–application of SKF–38393 and quinpirole is suggestive of a possible antagonistic interaction between D1–like and D2–like dopamine receptors on K⁺ channel activity.

Keywords: bipolar cells • retina: distal (photoreceptors, horizontal cells, bipolar cells) • ion channels