Inositol incorporation into phosphoinositides in retinal horizontal cells of Xenopus laevis: enhancement by acetylcholine, inhibition by glycine.

Abstract

The absorption of light by photoreceptor cells leads to an increased incorporation of [2-3H]inositol into phosphoinositides of horizontal cells in the retina of Xenopus laevis in vitro. We have identified several retinal neurotransmitters that are involved in regulating this response. Incubation with glycine, the neurotransmitter of an interplexiform cell that has direct synaptic input onto horizontal cells, abolishes the light effect. This inhibition is reversed by preincubation with strychnine. Acetylcholine added to the culture medium enhances the incorporation of [2-3H]inositol into phosphoinositides in horizontal cells when retinas are incubated in the dark. This effect is inhibited by preincubation with atropine. However, atropine alone does not inhibit the light-enhanced incorporation of [2-3H]inositol into phosphoinositides in the retina. gamma-Aminobutyric acid, the neurotransmitter of retinal horizontal cells in X. laevis, as well as dopamine and norepinephrine, have no effect on the incorporation of [2-3H]inositol into phosphoinositides. These studies demonstrate that the light-enhanced incorporation of [2-3H]inositol into phosphoinositides of retinal horizontal cells is regulated by specific neurotransmitters, and that there are probably several synaptic inputs into horizontal cells which control this process.

Receptor Activation and Inositol Lipid Hydrolysis in Neural Tissues

“…In the retina, light stimulation elicits an increased phosphoinositide turnover that is mediated in part by release of ACh (Anderson and Hollyfield, 198 I ;Anderson et al, 1983; Schmidt, 1983a,b) and can be blocked by administration of glycine (Anderson and Hollyfield, 1984). The inhibitory effect of glycine is, in turn, reversed by preincubation with strychnine.…”

“…Thus, although forskolin failed to reduce either carbamoylcholine-or norepinephrine-mediated stimulation of inositol lipid turnover in cerebral cortex slices (Hollingsworth and Daly, 1985), an inhibitory effect was observed by Nicchitta and Williamson (1986), using nerve ending preparations. Similarly, although it has been claimed that administration of excitatory amino acids (kainic acid, NMDA, or DL-homocysteate) exerts an inhibitory effect on phosphoinositide turnover elicited by carbamoylcholine, histamine, or K+ depolarization, and not by norepinephrine (Baudry et al, 1986), an inhibition of norepinephrinelinked, and not of carbamoylcholine-linked, stimulation was observed by Nicoletti et al (1986b).In the retina, light stimulation elicits an increased phosphoinositide turnover that is mediated in part by release of ACh (Anderson and Hollyfield, 198 I ;Anderson et al, 1983; Schmidt, 1983a,b) and can be blocked by administration of glycine (Anderson and Hollyfield, 1984). The inhibitory effect of glycine is, in turn, reversed by preincubation with strychnine.…”

Signaling roles of phosphoinositides in the retina

“…In 1981, Anderson and Hollyfield ( 11 ) reported that light stimulates the incorporation of inositol in the vertebrate retina. Light has also been shown to stimulate the generation of PIs in horizontal cells of the retina ( 12 , 13 ). Subsequent studies showed that light adaptation of bovine retinas in situ stimulates PI synthesis in retinal rod outer segment (ROS) membranes in vitro ( 5 ).…”

“…Subsequent studies showed that light adaptation of bovine retinas in situ stimulates PI synthesis in retinal rod outer segment (ROS) membranes in vitro ( 5 ). The work described in 1983 and 1984 by Anderson and colleagues revealed a functional significance in photoreceptor horizontal cell synapses ( 12 , 13 ). Light stimulates the PI metabolism in these cells, and these PIPs are important for synaptic ribbon formation, glutamate release, and signaling ( 12 , 13 ).…”

“…There is an active PI metabolism in the vertebrate retina and ROSs ( 6 , 7 , 8 , 12 , 13 , 20 , 21 , 22 , 25 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ). Light has been shown to stimulate several enzymes that are involved in PI metabolism, such as class I PI3K ( 7 , 52 ), class III PI3K ( 53 , 54 ), PI synthetase ( 5 ), DAG kinase ( 6 ), phosphatidylethanolamine N-methyltransferase ( 55 ), phospholipase A2 ( 56 ), phospholipase D ( 57 ), PLC ( 58 , 59 , 60 , 61 ), PKC ( 62 ), lipid phosphate phosphatase ( 63 ), and DAG lipase ( 37 ).…”