Ca2+ modulation of the cGMP-gated channel of bullfrog retinal rod photoreceptors.
AUTOR(ES)
Nakatani, K
RESUMO
1. The outer segment of an isolated rod photoreceptor from the bullfrog retina was drawn into a pipette containing choline solution for recording membrane current. The rest of the cell was sheared off with a glass probe to allow internal dialysis of the outer segment with a bath potassium solution ('truncated rod outer segment' preparation). The potential between the inside and the outside of the pipette was held at 0 mV. 2. Application of bath cGMP, in the presence of 3-isobutyl-1-methylxanthine (IBMX), gave rise to an outward membrane current. At saturating cGMP concentrations, this current was insensitive to intracellular Ca2+ at concentrations between 0 and 10 microM. At subsaturating cGMP concentrations, however, this current was inhibited by intracellular Ca2+. This sensitivity to Ca2+ declined after dialysis with a low-Ca2+ solution, suggesting the involvement of a soluble factor. 3. At low (nominally 0) Ca2+, the half-maximal activation constant and Hill coefficient for the activation of the cGMP-gated current by cGMP were 27 microM and 2.0, respectively. At high (ca 10 microM) Ca2+, the corresponding values were 40 microM cGMP and 2.4. 4. The inhibition of the current by Ca2+ was characterized at 20 microM cGMP. Ca2+ inhibited the current by up to 60%, with half-maximal inhibition at 48 nM Ca2+ and a Hill coefficient of 1.6.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1157922Documentos Relacionados
- Permeability and interaction of Ca2+ with cGMP-gated ion channels differ in retinal rod and cone photoreceptors.
- Block of the cGMP-gated cation channel of catfish rod and cone photoreceptors by organic cations.
- Subunit 2 (or beta) of retinal rod cGMP-gated cation channel is a component of the 240-kDa channel-associated protein and mediates Ca(2+)-calmodulin modulation.
- Antagonists of the cGMP-gated conductance of vertebrate rods block the photocurrent in scallop ciliary photoreceptors.
- Diacylglycerol analogs inhibit the rod cGMP-gated channel by a phosphorylation-independent mechanism.