Muscarinic stimulation of inositol phosphate formation in rat retina: developmental changes

The stimulation of inositol phosphates by various cholinergic agonists and the effect of antagonists was studied in rat retinal slices of different ages. The potency order of muscarinic agonists and antagonists for receptors linked to inositol phosphate production was the same for retinas of all ages. The maximum stimulation of inositol phosphate production varied between retinas of different ages, being greatest in the younger animals and lowest in the adult. However, no difference was found in the EC50 values. This contrasts with the neurotransmitters, noradrenaline and serotonin, both known to stimulate phosphoinositide metabolism; neither was found to have the same developmental profile of carbachol-induced stimulation of inositol phosphates. In contrast to the muscarinic receptors linked to phosphoinositide hydrolysis, the density of muscarinic binding sites measured by [3H]QNB binding increased in retinas during development. The affinity constants (KD) remained constant, however. The results are interpreted as suggesting that muscarinic receptors linked to inositol phosphate production are more efficiently coupled (to a guanine regulator protein) in retinas of young animals than in the adult.