INHIBITION BY NEOMYCIN OF POLYPHOSPHOINOSITIDE TURNOVER IN SUBCELLULAR FRACTIONS OF GUINEA-PIG CEREBRAL CORTEX IN VITRO

The addition of 10 −5 M to 10 −3 M neomycin to incubations of subcellular fractions of guinea-pig cerebral cortex increased the labelling of phosphatidylinositol phosphate and decreased the labelling of phosphatidylinositol diphosphate by [Γ- 32 P]ATP. The effect was observed in all subcellular fractions tested and depended on the cationic form of the antibiotic. Similar effects on lipid labelling were exerted by related aminoglycosidic antibiotics, by neamine, spermine and poly-L-lysine. Other neomycin fragments, antibiotics, local anesthetics or small polyamines were ineffective. Neomycin also inhibited the enzymatic hydrolysis of 32 P-polyphosphoinositides. The addition of the drug to aqueous dispersions of these lipids increased the turbidity and lowered the pH of the suspensions. It is suggested that the effects of neomycin on polyphosphoinositide metabolism result from the formation of an ionic complex between the lipids and the antibiotic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66456/1/j.1471-4159.1976.tb00318.x.pd

Sound Stimulates Labeling of Polyphosphoinositides in the Auditory Organ of the Noctuid Moth

The Noctuid moth possesses a simple auditory structure suitable for the investigation of biochemical correlates of sound stimulation in vivo. Stimulation with pulsed tones increased 32 P incorporation into polyphos-phoinositides but not into ATP or other lipids. The effect was seen in the scoloparium (sensory structure) but hot in the nodular sclerite, an adjacent nonsensory tissue. It was also not seen when the stimulus was a continuous tone, leading to adaptation of the action potential.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65812/1/j.1471-4159.1980.tb11201.x.pd

DETERGENT-LIKE ACTION OF TETRAPHENYLBORATE ON PHOSPHOLIPID LABELLING IN GUINEA PIG CORTEX SUBFRACTIONS 1

—The addition of 2 × 10 −4 m sodium tetraphenylborate to particulate preparations of guinea pig cerebral cortex increases labelling of phosphatidic acid from Γ-[ 32 P]-ATP two- to four-fold. The effect ‘was observed in all subcellular fractions studied (nuclear, synaptosomal, mitochondrial and microsomal) and is not blocked by the addition of atropine. Changes in phospholipid labelling similar to those induced by tetraphenylborate can be demonstrated with sodium dodecyl sulphate or sodium desoxycholate. It is suggested that tetraphenylborate stimulates lipid labelling by a detergent-like activation of diglyceride kinase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65419/1/j.1471-4159.1974.tb06881.x.pd

Polyphosphoinositides in insect muscle and sensory tissues

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66128/1/j.1471-4159.1979.tb04538.x.pd

Phospholipid labelling by [ 32 P]-orthophosphate and [ 3 H]-myo-inositol in the stimulated goldfish brain in vivo 1

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65519/1/j.1471-4159.1972.tb01470.x.pd

Hormonal regulation of adenylate cyclase in the stria vascularis of the mouse

The adenylate cyclase complex is a ubiquitous `second-messenger' system mediating the actions of hormones and neurotransmitters. Its presence but not its physiological control and function had previously been established in the cochlea.In this study, the hormonal stimulation of adenylate cyclase activity of the stria vascularis of the CBA mouse was characterized. In the presence of the regulatory nucleotide, GTP, the enzyme was stimulated by isoproterenol and epinephrine with a half-maximal effect at about 10 [mu]M and the stimulation was blocked by propranolol. This profile is consistent with the presence of adrenergic [beta]2-receptors on the strial enzyme complex. Hormones and neuromodulators preferring other receptor subtypes were ineffective; the non-specific stimulator, forskolin, activated the enzyme. The finding that potential hormonal effectors of water and ion transport including vasopressin were inactive may be significant with regard to the physiological role of strial adenylate cyclase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25788/1/0000350.pd

Calcium antagonism and reversibility of gentamicin-induced loss of cochlear microphonics in the guinea pig

The perilymphatic space of the guinea pig cochlea was perfused with various concentrations of Ca2+, Mg2+ and gentamicin. Cochlear microphonic potentials (CM) were essentially stable when solutions contained 1 mM Ca2+ plus 2 mM Mg2+, 1 mM Ca2+ and no Mg2+ or when both Ca2+ and Mg2+ were omitted. In the absence of Ca2+, the presence of 2 mM Mg2+ or 1 mM EGTA markedly decreased CM.Addition of 3 mM gentamicin lowered CM, the magnitude of the effect depending on the concentration of Ca2+ present. Ten mM Ca2+ eliminated the action of the drug. In the absence of Ca2+, the effects of Mg2+ and gentamicin were additive.When the application of gentamicin was followed by perfusion with drug-free medium, suppression of CM by 3 mM drug could be reversed with 10 mM Ca2+ but not with 1 mM Ca2+. Loss of CM was irreversible when administration of 10 mM Ca2+ was delayed or when the drug concentration was increased to 10 mM.The results are consistent with our previous hypothesis of a biphasic mechanism of aminoglycoside toxicity: an initial action competitive with calcium ions and reversible and a second step, non-competitive and irreversible.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23845/1/0000084.pd

Receptor-mediated release of inositol phosphates in the cochlear and vestibular sensory epithelia of the rat

Various neurotransmitters, hormones and other modulators involved in intercellular communication exert their biological action at receptors coupled to phospholipase C (PLC). This enzyme catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) to inositol 1,4,5-trisphosphate (InsP3) and 1,2-diacylglycerol (DG) which act as second messengers. In the organ of Corti of the guinea pig, the InsP3 second messenger system is linked to muscarinic cholinergic and P2y purinergic receptors. However, nothing is known about the the InsP3 second messenger system in the vestibule. In this study, the receptor-mediated release of inositol phosphates (InsPs) in the vestibular sensory epithelia was compared to that in the cochlear sensory epithelia of Fischer-344 rats. After preincubation of the isolated intact tissues with myo-[3H] in-ositol, stimulation with the cholinergic agonist carbamylcholine or the P2 purinergic agonist ATP-[gamma]-S resulted in a concentration-dependent increase in the formation of [3H]InsPs in both epithelia. Similarly, the muscarinic cholinergic agonist muscarine enhanced InsPs release in both organs, while the nicotinic cholinergic agonist dimethylphenylpiperadinium (DMPP) was ineffective. The muscarinic cholinergic antagonist atropine completely suppressed the InsPs release induced by carbamylcholine, while the nicotinic cholinergic antagonist mecamylamine was ineffective. Potassium depolarization did not alter unstimulated or carbamylcholine-stimulated release of InsPs in either organ. In both tissues, the P2 purinergic agonist [alpha],[beta]-methylene ATP also increased InsPs release, but the P1 purinergic agonist adenosine did not. These results extend our previous observations in the organ of Corti of the guinea pig to the rat and suggest a similar control of the InsP3 second messenger system in the vestibular sensory epithelia. In contrast to the cochlear sensory epithelia, atropine also significantly suppressed unstimulated InsPs release in the vestibular sensory epithelia. This suggests that the physiological mechanisms of the efferent nervous systems involving InsP3 second messenger system might be different in vestibular versus cochlear sensory epithelia.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30596/1/0000233.pd

Formation of a cytotoxic metabolite from gentamicin by liver

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28302/1/0000056.pd

ATP and Nitric Oxide Modulate Intracellular Calcium in Isolated Pillar Cells of the Guinea Pig Cochlea

Supporting cells in the mammalian cochlea have recently received attention as potential targets of neurotransmitters, neuromodulators, and neurohumoral agents. Calcium homeostasis in Deiters' and Hensen's cells, for example, is regulated by ATP and nitric oxide. We studied the intracellular calcium concentration [Ca2+]i in isolated pillar cells of the guinea pig cochlea in response to extracellular ATP and nitric oxide using the fluorescent indicator fluo-3. [Ca2+]i increased rapidly and significantly throughout the pillar cell in response to a bolus of ATP or 2-methylthio ATP while a, b-methylene ATP was ineffective. The response to ATP was inhibited by suramin and Cibacron Blue but not by pyridoxal phosphate 6-azopheny1-2',4'-disulfonic acid. This pharmacological profile is consistent with a [Ca2+]i increase largely mediated by P2Y receptors. In Ca2+-free medium supplemented with EGTA, the response to extracellular ATP was reduced by 33%, suggesting a contribution of calcium influx to the overall effect. The ATP-induced increase of [Ca2+]i was attenuated by NO donors (sodium nitroprusside or diethylamine NONOate), and this attenuation was reversed by KT5823, an antagonist to protein kinase G. The results indicate the involvement of purinergic mechanisms and the nitric oxide/cyclic GMP/protein kinase G pathway in the regulation of [Ca2+]i in cochlear pillar cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42438/1/10162-2-4-399_10020399.pd