Avtor/Urednik		Akopian, Abram; Križaj, David; Witkovsky, Paul
Naslov		Both high- and low voltage-activated calcium currents contribute to the light-evoked responses of luminosity horizontal cells in the Xenopus retina
Tip		članek
Vir		Brain Res
Vol. in št.		Letnik 762, št. 1-2
Leto izdaje		1997
Obseg		str. 121-30
Jezik		eng
Abstrakt		We examined the contribution of two intrinsic voltage-dependent calcium channels to the light-evoked responses of a non-spiking retinal neuron, the horizontal cell (HC). HC's isolated from the Xenopus retina were studied by the whole cell version of the patch clamp. In a mixture of agents which suppressed Na- and K-dependent currents, we identified a transient, low voltage-activated Ca current suppressed by Ba2+ and blocked by Ni2+ (T-type) and a sustained, high voltage-activated, dihydropyridine-sensitive Ca current that was enhanced by Ba2+ (L-type). We made simultaneous intracellular recordings from rods and HC's in the intact, dark-adapted Xenopus retina. Under certain stimulus conditions, transient oscillations appeared in HC responses but were absent in rod light-evoked waveforms. One type of transient was seen at relatively hyperpolarized potentials (< -45 mV), was enhanced by Sr2+ and inhibited by Ni2+. It thus appears to depend on a T-type Ca-current. A second type of oscillation was seen to be superimposed on a prolonged depolarizing wave following light off in the HC and as spike-like depolarizations in rods. These oscillations were enhanced by Ba2+ and Sr2+, but blocked by the dihydropyridine, nifedipine, indicating their dependence on an L-type calcium conductance. All calcium-dependent oscillations were suppressed by 0.05-0.5 mM Co2+. Suppression of glutamate neurotransmission with CNQX or kynurenate, or glycine neurotransmission with strychnine, enhanced the HC oscillations.
Deskriptorji		6-CYANO-7-NITROQUINOXALINE-2,3-DIONE ADAPTATION, OCULAR ANIMALS CALCIUM CALCIUM CHANNELS ELECTROPHYSIOLOGY EXCITATORY AMINO ACID ANTAGONISTS GLUTAMIC ACID GLYCINE GLYCINE AGENTS ION CHANNEL GATING LIGANDS MEMBRANE POTENTIALS PERIODICITY PHOTIC STIMULATION RETINA STIMULATION, CHEMICAL STRYCHNINE XENOPUS LAEVIS