Phosphorylation of low molecular mass cytosolic proteins by protein kinase C and protein kinase A in the rabbit exocrine pancreas

Erythrocyte anion transporter and antibrain immunoreactivity in chorea-acanthocytosis. A contribution to etiology, genetics, and diagnosis

Novel structural and functional alterations in the erythrocyte anion transporter band 3 are described in one patient with definite, and in two patients with symptoms compatible with chorea-acanthocytosis, but without acanthocytes. Immunoblotting analysis shows increased fragmentation of band 3, and sulfate flux measurements indicate that anion transport activity is reduced in the erythrocytes of these patients. These changes are similar, but not identical to those observed during normal erythrocyte aging. In addition, distinct antibrain immunoreactivity was present in the plasma of these patients. A family study indicates that abnormal erythrocyte band 3 structure and function and antibrain immunoreactivity may be phenotypes of two independent, genetically determined factors, that are part of the heterogenic defect of chorea-acanthocytosis. The findings in the patients without acanthocytes indicate that the biochemical abnormalities may be related to a chorea-acanthocytosis-like, amyotrophic extrapyramidal movement disorder with axonal neuropathy. Measurement of erythrocyte sulfate transport and plasma antibrain immunoreactivity could be of use in establishing the diagnosis and further unravelling the genetic background of chorea-acanthocytosis and related syndromes.

Are thrombocyte membranes altered in Alzheimer's disease? A morphometric and biochemical study

Morphometric analysis of thrombocytes from patients with Alzheimer's disease, from patients with multi-infarct dementia, and from young and age-matched healthy control donors, did not reveal any Alzheimer-related increase in internal membranes. Biochemical analysis showed a reduced cholesterol content of thrombocyte membrane preparations from Alzheimer patients relative to age-matched controls, but not relative to multi-infarct dementia patients. Overall distribution of protein kinase C activity (PKC) between cytosol and membrane, in resting as well as in activated thrombocytes from Alzheimer patients, was similar to that in the control groups. However, both Alzheimer and multi-infarct dementia patients had lower cytosolic levels of basal kinase and PKC activities than age-matched controls, while only Alzheimer patients had lower cytoskeletal PKC activity than controls.

Protein kinase A modulates Ca(2+)- and protein kinase C-dependent amylase release in permeabilized rat pancreatic acini

The role of protein kinase A (PKA) in the release of amylase from permeabilized pancreatic acini was investigated. Addition of cyclic AMP (cAMP) to permeabilized acini resulted in a potentiation of Ca(2+)-dependent amylase release, shifting the Ca2+ dose/response curve leftwards. As with protein kinase C (PKC) activation, this is due to an increase in the time of active discharge. The effect of cAMP was shown to be blocked by two inhibitors of PKA, H89 and the PKI-(5-24)-peptide. At low concentration, cAMP synergizes from phorbol 12-myristate 13-acetate (PMA), while at optimal concentrations cAMP and PMA are additive. PKA and PKC appear to work via similar, but not identical mechanisms.

Dissimilar effects of the protein kinase C inhibitors, staurosporine and H-7, on cholecystokinin-induced enzyme secretion from rabbit pancreatic acini

The effects of two putative inhibitors of protein kinase C activity, staurosporine and H-7, on partially purified protein kinase C and amylase secretion from isolated rabbit pancreatic acini were investigated. Staurosporine dose-dependently inhibited amylase release stimulated by an optimal concentration of cholecystokinin C-terminal octapeptide. At a concentration of 100 nM, the drug inhibited the secretory response to the secretagogue by approximately 50%. At the same concentration, staurosporine inhibited 12-O-tetradecanoylphorbol 13-acetate-stimulated enzyme secretion by 90%. Moreover, the potentiating effect of this phorbol ester on cholecystokinin-induced amylase release was completely abolished in the presence of staurosporine. Interestingly, amylase release was decreased to the level observed with the combination of cholecystokinin and staurosporine. In contrast, H-7, potentiated rather than inhibited cholecystokinin-stimulated enzyme secretion, whereas the secretory response to 12-O-tetradecanoylphorbol 13-acetate was not affected by the drug. Both staurosporine and H-7, however, inhibited protein kinase C purified from exocrine pancreatic tissue. Kinetic analysis revealed that both compounds inhibited protein kinase C competitively with respect to ATP. The Ki value for staurosporine was 0.55 nM and for H-7 13.5 microM. Our results obtained with staurosporine are in line with a stimulatory role of protein kinase C in cholecystokinin-induced enzyme secretion from the exocrine pancreas. The results obtained with H-7 emphasize that care has to be taken in interpreting the biological effects of this drug.