Effect of blocking the Na+/K+ ATPase on Ca2+ extrusion and light adaptation in mammalian retinal rods

• Published in: Biophysical journal Vol. 69; no. 2; pp. 439 - 450
• Main Authors: Demontis, G.C., Ratto, G.M., Bisti, S., Cervetto, L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-08-1995
• Subjects: Adaptation, Ocular - drug effects; Adaptation, Ocular - physiology; Adaptation, Ocular - radiation effects; Animals; Biophysical Phenomena; Biophysics; Calcium - metabolism; Guinea Pigs; In Vitro Techniques; Ion Transport - drug effects; Light; Macaca nemestrina; Models, Biological; Retinal Rod Photoreceptor Cells - drug effects; Retinal Rod Photoreceptor Cells - metabolism; Retinal Rod Photoreceptor Cells - radiation effects; Sodium - metabolism; Sodium-Potassium-Exchanging ATPase - antagonists & inhibitors; Strophanthidin - pharmacology
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(95)79917-9

Membrane current and light response were recorded from rods of monkey and guinea pig by means of suction electrodes. The correlation between adaptation and the Na+/K+ pump was investigated by measuring light-dependent changes in sensitivity with and without inhibition of Na+/K+ ATPase by strophanthidin. Strophanthidin was found to reduce the dark current, to slow the time course of the photoresponse, and to increase light sensitivity. At concentrations between 20 and 500 nM, the pump inhibitor suppressed in a reversible way the current re-activation occurring during prolonged illumination and modified the light-dependent decrease in sensitivity, which in control conditions approximates to a Weber-Fechner function. The effects of the pump inhibitor on the adaptive properties of rods are associated with an increased time constant of the membrane current attributed to the operation of the Na+:Ca2+,K+ exchanger. The effects of rapid application of the pump inhibitor on the current re-activation are consistent with the idea that significant changes in the internal sodium occur in rods of mammals during background illumination and that they play an important role in the process of light adaptation.