Differential expression of voltage-gated K+ and Ca2+ currents in bipolar cells in the zebrafish retinal slice.
Whole-cell voltage-gated currents were recorded from bipolar cells in the zebrafish retinal slice. Two physiological populations of bipolar cells were identified. In the first, depolarizing voltage steps elicited a rapidly activating A-current that reached peak amplitude < or = 5 ms of step onset. IA was antagonized by external tetraethylammonium or 4-aminopyridine, and by intracellular caesium. The second population expressed a delayed rectifying potassium current (IK) that reached peak amplitude > or = 10 ms after step onset and did not inactivate. IK was antagonized by internal caesium and external tetraethylammonium. Bipolar cells expressing IK also expressed a time-dependent h-current at membrane potentials < -50 mV. Ih was sensitive to external caesium and barium, and was also reduced by Na+-free Ringer. In both groups, a calcium current (ICa) and a calcium-dependent potassium current (IK(Ca)) were identified. Depolarizing voltage steps > -50 mV activated ICa, which reached peak amplitude between -20 and -10 mV. ICa was eliminated in Ca+2-free Ringer and blocked by cadmium and cobalt, but not tetrodotoxin. In most cells, Ica was transient, activating rapidly at -50 mV. This current was antagonized by nickel. The remaining bipolar cells expressed a nifedipine-sensitive sustained current that activated between -40 and -30 mV, with both slower kinetics and smaller amplitude than transient ICa. IK(Ca) was elicited by membrane depolarizations > -20 mV. Bipolar cells in the zebrafish retinal slice preparation express an array of voltage-gated currents which contribute to non-linear I-V characteristics. The zebrafish retinal slice preparation is well-suited to patch clamp analyses of membrane mechanisms and provides a suitable model for studying genetic defects in visual system development.
Connaughton
V P
VP
University of Texas at Houston Medical School, Department of Neurobiology and Anatomy, 77030, USA. vikki@codon.nih.gov
Maguire
G
G
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000502:physiology*; D015027:Zebrafish
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels