Different pathways of [3H]inositol phosphate formation mediated by alpha 1a- and alpha 1b-adrenergic receptors

The types of inositol phosphates (InsPs) formed in response to activation of alpha 1-adrenergic receptor subtypes were determined in collagenase-dispersed renal cells and hepatocytes by high pressure liquid chromatography separation. In hepatocytes, which contain only the alpha 1b subtype, norepinephrine stimulated rapid (10-s) formation of [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4)P3 and slower (5-min) formation of Ins(1,4)P2 and Ins(1)P. Selective inactivation of alpha 1b receptors by chloroethylclonidine almost completely blocked the effects of norepinephrine in hepatocytes. In renal cells, which contain both alpha 1a and alpha 1b receptors in a 60:40 ratio, norepinephrine did not significantly increase the size of any peaks until 5 min after agonist activation. At this time, only a peak eluting with Ins(1)P and one eluting shortly after Ins(1,4)P2 were significantly elevated. Incubation with norepinephrine for 2 h caused small but significant increases in peaks co-eluting with Ins(1)P and Ins(1,4,5)P3 in renal cells; however, only the increase in Ins(1)P was inhibited by chloroethylclonidine pretreatment. Extraction under neutral conditions suggested that cyclic InsPs may be the primary compounds formed in response to norepinephrine in renal cells. Removal of extracellular Ca2+ caused a 60% reduction in the InsP response to norepinephrine in renal cells but had no effect in hepatocytes. These results suggest that activation of alpha 1a and alpha 1b receptor subtypes results in formation of different InsPs and that the response to alpha 1a activation may require influx of extracellular Ca2+.     

Plasma Amino-acids in the Nigerian Nutritional Ataxic Neuropathy

Investigation of nine patients with tropical ataxic neuropathy showed an absence or diminution of sulphur-containing amino-acids—cysteine and methionine—and a variable concentration of most other essential amino-acids. The pattern was unlike that found in kwashiorkor. The levels of serum cholesterol and total protein were normal, and the serum vitamin B₁₂ levels were normal or high. Plasma thiocyanate concentration was high.All the patients gave a history of a monotonous diet of cassava derivatives. Cassava contains a cyanogenetic glycoside (linamarin) from which cyanide is released on hydrolysis. The excessive cyanide detoxication may be responsible for the low concentration of the sulphur-containing amino-acids.