The effects of quinidine on sodium-dependent calcium efflux in isolated rod photoreceptors of the salamander retina
✍ Scribed by Leon Lagnado; Peter A. McNaughton
- Publisher
- Springer
- Year
- 1990
- Tongue
- English
- Weight
- 638 KB
- Volume
- 417
- Category
- Article
- ISSN
- 0031-6768
No coin nor oath required. For personal study only.
✦ Synopsis
The effect of quinidine on the membrane current generated by the Na:Ca,K exchange has been investigated in the outer segment of isolated rod photoreceptors from the retina of the larval tiger salamander. The inward exchange current associated with the efflux of Ca 2+ was selectively recorded by introducing a Ca 2 § load through the lightsensitive channels, and then shutting these channels with a bright light. Quinidine (20-1000 ~M) reduced the magnitude of the exchange current and slowed its decay during the removal of a Ca 2+ load. Quinidine did not alter the form of the relation between the exchange current and the total concentration of exchangeable calcium remaining within the outer segment, [Ca]T, showing that it does not change the affinity of the exchange mechanism for internal Ca 2+. The relation between exchange current inhibition and the quinidine concentration could be described by a simple Michaelis relation with a Ki of 287 ~M and a maximum inhibition of 50 %. The incomplete block of the Na:Ca,K exchange current by quinidine shows that it does not act by simple competition with external Na +, and suggests that the inhibition of the exchange by quinidine may be non-specific.