The effects of quinidine on sodium-dependent calcium efflux in isolated rod photoreceptors of the salamander retina.
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 Ca2+ was selectively recorded by introducing a Ca2+ load through the light-sensitive channels, and then shutting these channels with a bright light. Quinidine (20-1000 microM) reduced the magnitude of the exchange current and slowed its decay during the removal of a Ca2+ 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 Ca2+. The relation between exchange current inhibition and the quinidine concentration could be described by a simple Michaelis relation with a Ki of 287 microM 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.
Lagnado
L
L
Physiological Laboratory, Cambridge, UK.
McNaughton
P A
PA
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D007700:Kinetics; D010786:Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011802:Quinidine / Q000494:pharmacology*; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000502:physiology*; D014562:Caudata
D012964:Sodium; D011802:Quinidine; D011188:Potassium; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine