A cGMP-gated current can control exocytosis at cone synapses.
The voltage-gated Ca2+ current in cone photoreceptors operates over only a small part of the physiological voltage range produced by light and, consequently, appears insufficient for controlling transmitter release. We have used a whole-cell voltage clamp to measure membrane current and the capacitance change produced by exocytosis in solitary cone and rod photoreceptors isolated from the salamander retina. In both types of photoreceptor, Ca2+ influx through voltage-gated Ca2+ channels initiated exocytosis. In addition, Ca2+ influx through a cGMP-gated channel in the inner segment and synaptic processes of cones also initiated exocytosis. The cGMP-gated current sustained exocytosis over the entire physiological voltage range.
Rieke
F
F
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Schwartz
E A
EA
D000557:Ambystoma; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D006152:Cyclic GMP / Q000494:pharmacology*; D054815:Cyclic Nucleotide-Gated Cation Channels; D004553:Electric Conductivity; D005089:Exocytosis / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects*; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials; D010786:Photoreceptor Cells / Q000502:physiology*; D012160:Retina / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D013569:Synapses / Q000502:physiology*
D015220:Calcium Channels; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D006152:Cyclic GMP