scholarly journals Control of the light-regulated current in rod photoreceptors by cyclic GMP, calcium, and l-cis-diltiazem.

1986 ◽  
Vol 83 (4) ◽  
pp. 1163-1167 ◽  
Author(s):  
J. H. Stern ◽  
U. B. Kaupp ◽  
P. R. MacLeish
Keyword(s):  
Cyclic Gmp ◽  
Rod Photoreceptors

scholarly journals Transduction persists in rod photoreceptors after depletion of intracellular calcium.

1987 ◽  
Vol 89 (2) ◽  
pp. 297-319 ◽  
Author(s):  
G D Nicol ◽  
U B Kaupp ◽  
M D Bownds
Keyword(s):  
Cyclic Gmp ◽  
Dark Current ◽  
Phosphodiesterase Inhibitor ◽  
Light Regulation ◽  
Response Duration ◽  
Light Sensitivity ◽  
Ionophore A23187 ◽  
Active Suspensions ◽  
Rod Photoreceptors ◽  
Intracellular Ca

We have examined the role of Ca++ in phototransduction by manipulating the intracellular Ca++ concentration in physiologically active suspensions of isolated and purified rod photoreceptors (OS-IS). The results are summarized by the following. Measurement of Ca++ content using arsenazo III spectroscopy demonstrates that incubation of OS-IS in 10 nM Ca++-Ringer's solution containing the Ca++ ionophore A23187 reduces their Ca++ content by 93%, from 1.3 to 0.1 mol Ca++/mol rhodopsin. Virtually the same reduction can be accomplished in 10 nM Ca++-Ringer's without ionophore, presumably via the plasma membrane Na/Ca exchange mechanism. Hundreds of photoresponses can be obtained from the Ca++-depleted OS-IS for at least 1 h in 10 nM Ca++-Ringer's with ionophore. The kinetics and light sensitivity of the photoresponse are essentially the same in the presence or absence of the ionophore in 10 nM Ca++. The addition of A23187 in 1 mM Ca++-Ringer's results in a Ca++ influx that rapidly suppresses the dark current and the photoresponse. This indicates that there is an intracellular site at which Ca++ can modulate the light-regulated conductance. Both the current and photoresponse can be restored if intracellular Ca++ is reduced by lowering the external Ca++ to 10 nM. During the transition from high to low Ca++, the response duration becomes shorter, which suggests that it can be regulated by a Ca++-dependent mechanism. If the dark current and the photoresponse are suppressed by adding A23187 in 1 mM Ca++-Ringer's, the subsequent addition of the cyclic GMP phosphodiesterase inhibitor isobutylmethylxanthine can restore the current and photoresponse. This implies that under conditions where the rod can no longer control its intracellular Ca++, the elevation of cyclic GMP levels can restore light regulation of the channels. The persistence of normal flash responses under conditions where intracellular Ca++ levels are reduced and perturbed suggests that changes in the intracellular Ca++ concentration do not cause the closure of the light-regulated channel.

scholarly journals A derivative of amiloride blocks both the light-regulated and cyclic GMP-regulated conductances in rod photoreceptors.

1987 ◽  
Vol 90 (5) ◽  
pp. 651-669 ◽  
Author(s):  
G D Nicol ◽  
P P Schnetkamp ◽  
Y Saimi ◽  
E J Cragoe ◽  
M D Bownds
Keyword(s):  
Plasma Membrane ◽  
Cyclic Gmp ◽  
Dark Current ◽  
Outer Segment ◽  
Light Response ◽  
Ionic Channels ◽  
Rod Photoreceptors ◽  
Low Concentrations ◽  
Excised Patches ◽  
Activated Flux

Vertebrate rod photoreceptors in the dark maintain an inward current across the outer segment membrane. The photoresponse results from a light-induced suppression of this dark current. The light-regulated current is not sensitive to either tetrodotoxin or amiloride, potent blockers of Na+ channels. Here, we report that a derivative of amiloride, 3',4'-dichlorobenzamil (DCPA), completely suppresses the dark current and light response recorded from rod photoreceptors. DCPA also blocks a cyclic GMP-activated current in excised patches of rod plasma membrane and a cGMP-induced Ca++ flux from rod disk membranes. These results are consistent with the notion that the Ca++ flux mechanism in the disk membrane and the light-regulated conductance in the plasma membrane are identical. DCPA also inhibits the Na/Ca exchange mechanism in intact rods, but at a 5-10-fold-higher concentration than is required to block the cGMP-activated flux and current. The blocking action of DCPA in 10 nM Ca++ is different from that in 1 mM Ca++, which suggests either that the conductance state of the light-regulated channel may be modified in high and low concentrations of Ca++, or that there may be two ionic channels in the rod outer segment membrane.

scholarly journals Interactions between the subunits of transducin and cyclic GMP phosphodiesterase in Rana catesbiana rod photoreceptors.

1990 ◽  
Vol 265 (20) ◽  
pp. 11539-11548 ◽  
Author(s):  
A Yamazaki ◽  
F Hayashi ◽  
M Tatsumi ◽  
M W Bitensky ◽  
J S George
Keyword(s):  
Cyclic Gmp ◽  
Rod Photoreceptors

Evidence that cyclic GMP regulates membrane potential in rod photoreceptors

Nature ◽  
1979 ◽  
Vol 280 (5717) ◽  
pp. 64-66 ◽  
Author(s):  
WILLIAM H. MILLER ◽  
GRANT D. NICOL
Keyword(s):  
Membrane Potential ◽  
Cyclic Gmp ◽  
Rod Photoreceptors

Cycle GMP-activated channels of rod photoreceptors show neither fast nor slow desensitization

1990 ◽  
Vol 4 (05) ◽  
pp. 481-487 ◽  
Author(s):  
Shu-Ichi Watanabe ◽  
Gary Matthews
Keyword(s):  
Cyclic Gmp ◽  
Outer Segment ◽  
Flow System ◽  
Rod Photoreceptors ◽  
Rapid Flow ◽  
Inside Out

AbstractDesensitization of cGMP-activated channels was examined in excised, inside-out patches obtained from rod photoreceptors. Cyclic GMP was applied using a rapid-flow system in which concentration jumps are complete within 10–50 ms. In outer-segment patches containing many channels, the cGMP-dependent conductance reached a steady plateau that was maintained for tens of seconds in the presence of cGMP; thus, there was no indication of slow desensitization. However, rapid desensitization on the scale of milliseconds could not be ruled out because of limited speed of access of cGMP to the inner face of the patch membrane. To test for rapid desensitization, inner-segment patches containing only a single cGMP-activated channel were used. In these one-channel patches, there was no change in activity of the channel with time from its earliest onset after application of cGMP, indicating that rapid desensitization also did not occur.

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