The neuropeptide galanin is widely expressed in the central nervous system and other tissues and induces different cellular reactions, e.g. hormone release from pituitary and inhibition of insulin release from pancreatic B cells. By microinjection of antisense oligonucleotides we studied the question as to which G proteins mediate the galanin‐induced inhibition of voltage‐gated Ca2+ channels in the rat pancreatic B‐cell line RINm5F and in the rat pituitary cell line GH3. Injection of antisense oligonucleotides directed against alpha 01, beta 2, beta 3, gamma 2 and gamma 4 G protein subunits reduced the inhibition of Ca2+ channel current which was induced by galanin, whereas no change was seen after injection of cells with antisense oligonucleotides directed against alpha i, alpha q, alpha 11, alpha 14, alpha 15, beta 1, beta 4, gamma 1, gamma 3, gamma 5, or gamma 7 G protein subunits or with sense control oligonucleotides. In view of these data and of previous results, we conclude that the galanin receptors in GH3 and in RINm5F cells couple mainly to the G(0) protein consisting of alpha 01 beta 2 gamma 2 to inhibit Ca2+ channels and use alpha 01beta 3 gamma 4 less efficiently. The latter G protein composition was previously shown to be used by muscarinic M4 receptors to inhibit Ca2+ channels.

Mevalonic aciduria due to mevalonate kinase deficiency, an inherited defect of cholesterol biosynthesis, has presented with clinical variability in 10 patients from 7 families. We sought to define a genetic basis for this heterogeneity by determining mevalonate kinase activity in fibroblast heterokaryons obtained by polyethylene glycol fusion. To this end we developed a DEAE-cellulose (Cl-) column chromatography procedure for assessing mevalonate kinase in cell extracts that would allow multiple rapid analyses. Fusion of control fibroblasts with those from affected patients from six families with mevalonate kinase deficiency yielded 37% of the mean control activity. None of the fusions between the six cell lines of patients resulted in measurable mevalonate kinase activity. Using the chromatographic procedure, we developed an optimized assay for mevalonate kinase in biopsied chorionic villi. Km values for chorionic villi were similar to those obtained in fibroblasts. Mevalonate kinase activity in biopsied chorionic villi showed a linear increase (0.75-4.3 nmol/min per mg protein) with gestational age from 7 to 14 weeks. Using the optimized assay in biopsied chorionic villi we performed a first-trimester prenatal diagnosis in a pregnancy at risk for mevalonate kinase deficiency and correctly diagnosed an unaffected fetus. The availability of an optimized assay for mevalonate kinase in biopsied chorionic villi should allow reliable first-trimester prenatal diagnosis for families at risk.

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In a search for the pathophysiologic mechanisms, we estimated isoprenoid synthesis and concentration, cellular growth, and the activity of the LDL receptor pathway in fibroblasts from patients with mevalonate kinase deficiency (MKD), a severe multisystemic disorder of cholesterol and non-sterol isoprenoid biosynthesis. In response to different concentrations of LDL and non-lipoprotein-bound cholesterol, MKD cells partially counteracted their enzyme defect by increased activities of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase (results from earlier studies) and the LDL receptor pathway, responses similar to the pharmacologic effects seen upon administration of HMG-CoA reductase inhibitors. Rates of N-linked protein glycosylation, estimated as the amount of [14C]galactose-labeled macromolecules secreted into cell culture medium, were significantly decreased in MKD fibroblasts in comparison with control cells which may indicate alterations in the dolichol or dolichol phosphate pool. In response to exogenous cholesterol, the major feedback inhibitor of isoprenoid biosynthesis, growth velocities of MKD fibroblasts declined in comparison with control cells, further suggesting an impairment of non-sterol isoprenoid biosynthesis in MKD. Our results suggest an imbalance in the multilevel regulation of the biosynthesis of cholesterol and non-sterol isoprenoids in MKD, representing an additional causative factor responsible for the pre- and postnatal pathology of MKD.