Intracellular injection of cyclic-GMP increases sodium conductance in gecko photoreceptors.
In order to examine the possibility that cyclic-GMP is an internal transmitter in the process of phototransduction, cyclic-GMP was iontophoretically injected into a gecko photoreceptor from one barrel of a double-barrelled microelectrode with the other barrel monitoring membrane potential and conductance changes. Cyclic-GMP induced a prolonged depolarization accompanied by a marked increase in membrane conductance. In the sodium-free bathing solution (substituted by choline), injection of cyclic-GMP did not cause any depolarization. The cells, which showed the cyclic-GMP-induced depolarization, produced no significant potential changes with injection of 5'-GMP or cyclic-AMP, indicating that the depolarization was cyclic-GMP-specific. The results suggest that cyclic-GMP is involved in the phototransduction process in the gecko photoreceptors. However, uncertainty still remained as to whether the cyclic-GMP level directly correlates with the photoreceptor membrane potential.
D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D007478:Iontophoresis; D008116:Lizards; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D010786:Photoreceptor Cells / Q000187:drug effects* / Q000502:physiology; D012964:Sodium / Q000502:physiology*
D007473:Ion Channels; D012964:Sodium; D000242:Cyclic AMP; D006152:Cyclic GMP