Dihydropyridine-sensitive calcium currents in bipolar cells of salamander retina are inhibited by reductions in extracellular chloride.
Dihydropyridine-sensitive calcium currents (I(Ca)) in photoreceptors are unusual in that they can be inhibited by reductions in extracellular chloride. The present study examined whether I(Ca) in retinal bipolar cells, which as in photoreceptors mediates sustained neurotransmission, is also inhibited by reductions in chloride. Nystatin-perforated patch, whole cell recordings were obtained from bipolar cells in a retinal slice preparation of larval tiger salamander. In the presence of Ba(2+), voltage steps above -40 mV evoked sustained inward currents, which were enhanced by the dihydropyridine, (-)BayK8644, and inhibited by nisoldipine. Similar to photoreceptors, replacing Cl(-) with gluconate or CH(3)SO(4) inhibited bipolar cell I(Ca) and produced a negative shift in the current/voltage relationship. Thus, sensitivity to Cl(-) may be a more general property of L-type Ca(2+) channel subtypes that mediate sustained neurotransmission.
Thoreson
W B
WB
Departments of Ophthalmology and Pharmacology, University of Nebraska Medical Center, 985540, Omaha, NE 68198-5540, USA. wbthores@unmc.edu
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000557:Ambystoma; D000818:Animals; D001464:Barium / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002712:Chlorides / Q000494:pharmacology / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology*; D005942:Gluconates / Q000494:pharmacology; D066298:In Vitro Techniques; D007814:Larva; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D015737:Nisoldipine / Q000494:pharmacology; D009761:Nystatin / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects / Q000502:physiology*; D012160:Retina / Q000166:cytology* / Q000502:physiology
D020746:Calcium Channels, L-Type; D002712:Chlorides; D004095:Dihydropyridines; D005942:Gluconates; D009761:Nystatin; D001464:Barium; D015737:Nisoldipine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; C030691:gluconic acid