Dihydropyridine-sensitive Ca2+ spikes and Ca2+ currents in rabbit ciliary body epithelial cells.
Intracellular microelectrode and whole-cell patch-clamp recordings were used to investigate a Ba(2+)-induced regenerative depolarization and its underlying Ba2+ current in the ciliary body epithelial cells of the rabbit eye. Exposure of these epithelial cells to 4-10 mmol l-1 Ba2+ depolarized the membrane potential and caused the generation of one or more spikes, before the membrane potential reached a steady-state level. The spikes, but not the slow phase of depolarization, could be blocked with Co2+ (2 mmol l-1), Gd3+ (25 mumol l-1), La3+ (20 mumol l-1), Cd2+ (10 mumol l-1), verapamil (30 mumol l-1) and nifedipine (1 mumol l-1). Tetrodotoxin at 100 nmol l-1 had no effect. In the absence of Na+, but in the presence of external Ba2+, step depolarization of the membrane potential activated an inward current that could be blocked with Co2+ (2 mmol l-1), Cd2+ (10 mumol l-1) and nifedipine (1 mumol l-1), but not with Ni2+ (50 mumol l-1) or omega-conotoxin (1-10 mumol). This inward current could be enhanced with the dihydropyridine agonist (+/-)BAY K 8644 (1 mumol l-1). The inactivation characteristics of the inward current (v1/2 = -38.7 mV, k = 12.6 mV) is most like that seen in neurons. These findings indicate that the epithelial cells of the ciliary body possess dihydropyridine-sensitive, voltage-activated Ca2+ channels.
Farahbakhsh
N A
NA
Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles 90024.
Cilluffo
M C
MC
Chronis
C
C
Fain
G L
GL
D000200:Action Potentials; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002924:Ciliary Body / Q000378:metabolism / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology*; D004848:Epithelium / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects; D011817:Rabbits
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D015221:Potassium Channels; D001464:Barium; D002118:Calcium