Sodium nitroprusside alters dark voltage and light responses in isolated retinal rods during whole-cell recording

Abstract

Dark voltage and light responses of isolated retinal rods of Rana esculenta were investigated by employing the whole-cell patch-clamp technique. When the recording pipette was filled with a medium devoid of nucleotides, a spontaneous hyperpolarization of the dark voltage partly due to a diffusional loss of cGMP and its precursor GTP and a retardation in the recovery of the light responses was observed. The larger part of the retardation of the light responses was prevented by 1 mM ATP. Addition of GTP attenuated the hyperpolarization, but did not abolish it completely. When the nitric-oxide-releasing substance sodium nitroprusside plus GTP was applied, the tendency of hyperpolarization disappeared and a stable dark voltage or even a slight depolarization was measured during the whole-cell recording period. Similar results were also obtained when GTP was given in combination with either EGTA or IBMX which are both known to interfere with the cGMP regulating enzymes in retinal rods. In addition to its effects on the dark voltage, an acceleration of the recovery phase of the light responses by sodium nitroprusside was also observed. Our observations strongly suggest that sodium nitroprusside activates guanylate cyclase in photoreceptors, as it does in other tissues, but we cannot exclude with certainty an effect on the phosphodiesterase.

Calcium store depletion potentiates a phosphodiesterase inhibitor‐ and dibutyryl cGMP‐evoked calcium influx in rat pituitary GH3 cells

“…Since cGMP is formed in bation with 1 ktM nicardipine, or 1 p~M verapamil (data not mammalian cells by the guanylate cyclase catalysed hydrolysis shown). A possible explanation for the observed potentiation of GTP [21], the above procedure may have resulted in the in the cGMP-evoked increase in [CaZ+]i following Ca 2+ store inhibition of guanylate cyclase, and a corresponding decrease depletion is a decrease in cytoplasmic Ca 2+ buffering due to in the free cytoplasmic level of cGMP in the above studies. If inhibition of Ca 2+ uptake into stores by thapsigargin.…”

Purified retinal nitric oxide synthase enhances ADP‐ribosylation of rod outer segment proteins

“…There is also evidence from recent studies that NO is involved in several different processes in the vertebrate retina, for example it influences light responses of amphibian rods [4,5], it activates a soluble guanylyl cyclase and modulates a Ca 2+ channel and a voltage-independent conductance in inner segments of photoreceptors [6,7]. Effects of NO were also recorded on hemi-gap junction channels in horizontal cells [8], on cGMP-gated cation channels in retinal ganglion [9] and on-bipolar cells [10].…”

Differentiation of short-wavelength-sensitive cones by NADPH diaphorase histochemistry.

“…This is supported by evidence that NADPH diaphorase is a NOS (8,9) as well as by evidence that NO plays a functional role in the outer retina. Involvement of NO in photoreceptor function is (15)(16)(17)(18), (ii) photoreceptor responses to light are modulated by NO relevant substances (e.g., NO releasing substance sodium nitroprusside, NADPH, arginine) (15), and (iii) NOS has been localized in salamander rod and cone ellipsoids by immunocytochemistry (23) and in bovine rod outer segments by enzymatic assay (17). Furthermore, other studies have suggested that NO may be involved in the process of photoreceptor adaptation (15).…”

“…Involvement of NO in photoreceptor function is (15)(16)(17)(18), (ii) photoreceptor responses to light are modulated by NO relevant substances (e.g., NO releasing substance sodium nitroprusside, NADPH, arginine) (15), and (iii) NOS has been localized in salamander rod and cone ellipsoids by immunocytochemistry (23) and in bovine rod outer segments by enzymatic assay (17). Furthermore, other studies have suggested that NO may be involved in the process of photoreceptor adaptation (15). The possibility that inner segment NADPH diaphorase labeling may result from the presence of an oxidative enzyme other than NOS has been raised by results in rat retina (24), although those results may simply reflect the involvement of a different NOS isoenzyme.…”

“…As a neural messenger, neuronal nitric oxide (NO) diffuses across cellular membranes to activate soluble guanylate cyclase, which in turn increases intracellular levels of second messenger cGMP (11). NO has been implicated in synaptic transmission and plasticity (12)(13)(14) and also in photoreceptor function (15)(16)(17)(18). In the vertebrate retina, NADPH…”