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Modulation by internal protons of native cyclic nucleotide-gated channels from retinal rods
C Picco1, C Sanfilippo, P Gavazzo
1Istituto di Cibernetica e Biofisica, C.N.R, Genova, Italy.
The Journal of General Physiology
|October 1, 1996
Summary
Internal pH significantly affects cyclic nucleotide-gated channels in retinal rods. Lowering pH reduces cGMP-activated current but alters cAMP activation by affecting both current and open probability.
Area of Science:
- Neuroscience
- Molecular Biology
- Biophysics
Background:
- Cyclic nucleotide-gated (CNG) channels are crucial for phototransduction in retinal rod outer segments.
- These channels are known to be modulated by various factors, including intracellular pH (pH(i)).
Purpose of the Study:
- To investigate the impact of varying intracellular pH on the function of native CNG channels in salamander retinal rods.
- To characterize the differential effects of pH on channels activated by cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP).
Main Methods:
- Excised membrane patches from salamander retinal rod outer segments were utilized.
- Ion channel currents were measured using patch-clamp electrophysiology.
- Channels were activated by cGMP or cAMP, and current-voltage relationships and concentration-response curves were analyzed at different intracellular pH levels (7.6 to 5.0).
Main Results:
- Increasing proton concentration (decreasing pH(i)) reduced the single-channel current activated by cGMP, consistent with protonation of a single acidic residue (pK(1) = 5.1).
- For cAMP-activated channels, decreasing pH(i) decreased the cGMP concentration for half-maximal activation (K(1/2)) and initially increased maximal currents before decreasing them below pH 5.5.
- These cAMP effects were attributed to reduced single-channel current and increased channel open probability due to proton binding at sites with a pK(2) of 6.
Conclusions:
- Intracellular pH acts as a significant modulator of CNG channel activity in retinal rods.
- The differential effects of pH on cGMP and cAMP activation highlight complex regulatory mechanisms involving protonation events that influence both channel conductance and gating.