Electrical activity in non-neuronal cells can be induced by altering the membrane potential and eliciting action potentials. For example, hormones, nutrients and neurotransmitters act on excitable endocrine cells. In an attempt to correlate such electrical activity with regulation of cell activation, we report here direct measurements of cytosolic free Ca2+ changes coincident with action potentials. This was achieved by the powerful and novel combination of two complex techniques, the patch clamp and microfluorimetry using fura 2 methodology. Changes in intracellular calcium concentration were monitored in single cells of the pituitary line GH3B6. We show that a single action potential leads to a marked transient increase in cytosolic free calcium. The size of these short-lived maxima is sufficient to evoke secretory activity. The striking kinetic features of these transients enabled us to identify oscillations in intracellular calcium concentration in unperturbed cells resulting from spontaneous action potentials, and hence provide an explanation for basal secretory activity. Somatostatin, an inhibitor of pituitary function, abolishes the spontaneous spiking of free cytosolic Ca2+ which may explain its inhibitory effect on basal prolactin secretion. Our data therefore demonstrate that electrical activity can stimulate Ca2+-dependent functions in excitable non-neuronal cells.

No abstract

Studies on islet cell regeneration, hyperplasia and intrainsular cellular interrelations in long.lasting streptozotocin diabetes in ratsSummary. Diabetes was induced in rats with various single i.v. doses of streptozotocin. The rats were killed 4--10 months thereafter. Marked hyperglycaemia, ketonaemia and a rise of plasma free fatty acids resulted. The weight increase was markedly reduced. There was a clear reciprocal correlation between the injected dose of the diabetogenic agent and plasma IRI. The same was true for the B-cell counts. There was a marked B-cell hypertrophy, whereas we found only slight indication for B-cell regeneration. In one animal a functioning B-cell adenoma developed and almost all the parameters tested were normalized. In the diabetic animals the Ae-eells were predominant in the islets of Langerhans and their mean nuclear diameters were increased. In the duodenal nmeosa no increase in the number of glucagonoeytes was found.We interpret this activity of the glueagonoeytes as a consequence of permanent and long-lasting hyperglyeaemia. Investigations sur la regdndration et l'hyperplasie des cellules dans les ilots de Langerhans et sur les interrelations cellulaires intrainsulaires dans le diab~te de longue durde provoqud par la streptozotocine chez le ratRdsumd. Par des doses diffgrentes de Streptozotocine i.v. on provoque chez des rats un diab6te d'une durde de 4 ~ 10 tools. On note une hyperglyc6mie sdv~re, une ac6ton@mie et une augmentation moddr6e des acides gras. La prise de poids est diminude de fagon marqude. --I1 existe une nette eorrdlation rdeiproque entre la quantitd d'agent diab@tog~ne injeetd et l'insuline immunordactive plasmatique (IRI). On trouve le m@me rapport entre le nombre des cellules Bet Ia quantitd de Streptozotocine. On note unc eorrdlation direete entre le nombre des eellules Bet I'IRI. --L'hypertrophie des eellules B est importante alors qu'on ne trouve que pea de signes de r@gdndration des ilots et des eellules B. --Chez un des rats on note l'apparition d'un addnome ~ cellules B fonctionnant, provoquant une normalisation du m6tabolisme glueidique. --Chez les animaux diabdtiques, les cellules A 2 prgdominent et le diam~tre moyen des noyaux est augment6. On ne note pas d'augmentation signifieative des glueagonoeytes de la muqueuse duod6nale.Nous consid@rons que eette augmentation de l'aetivit@ des glucagonoeytes est fonction de l'hyperglyedmie perm~nente et de longue durge.

The cytosolic free calcium concentration, [Ca2+]i, was monitored in single rat lactotrophs in primary culture with the fluorescent probe Fura 2. It was found that lactotrophs are very heterogeneous in their [Ca2+]i response to TRH and dopamine, the major physiological regulators of PRL secretion. While in most lactotrophs TRH raises [Ca2+]i, the kinetics of this rise and the magnitude of its first and second phases vary considerably. For dopamine two clearly divergent response types can be observed. In part of the lactotrophs dopamine causes a lowering of [Ca2+]i from elevated levels, whereas in about 40% of the lactotrophs dopamine leads to a transient rise of [Ca2+]i. The present study reveals subclasses of lactotrophs with distinct [Ca2+]i response characteristics. It is suggested that such response type heterogeneity is a means of optimizing the secretory response to the complex regulatory influences on the pituitary.

Six maturity onset diabetic patients took glibenclamide 5 mg by mouth, every morning 10 min before a standard breakfast. Serum levels of immunoreactive glibenclamide, glucose and immunoreactive insulin were measured repeatedly on the first and 15th days of treatment. Measured glibenclamide blood levels were in close agreement with an analogue computer simulation of data obtained from healthy volunteers: there was no accumulation of drug in the blood, but there was strong evidence for the existence of a slowly equilibrating "deep" compartment. Considerable insulin release and correction of the breakfast-induced hyperglycaemia were observed immediately after administration of the drug, as well as 5 h later, at lunch time. The clinical significance of blood levels of glibenclamide, as well as the correlation of pharmacokinetics with pharmacodynamics, are discussed in the light of these results.

Four subjects received 5 mg laC-glipizide orally and 3 subjects 1 mg intravenously. The average absorption of the oral dose was nearly 100% with peak plasma levels occurring between 90 and 360 min. The apparent half-life of plasma radioactivity was approximatively 3.7 h, the disappearance of radioactivity following complex kinetics due to metabolism of the drug. Extraction with CI-t2C12 and chromatography showed that in plasma 85% of the total radioactivity corresponded to unchanged glipizide, but in urine 98o/o to more polar and more readily excreted metabolites. The urinary excretion is 68% of t}le dose. The hypoglyeaemie effect of glipizide is comparable to glibenelamide. The administration of 14C-glipizide to two patients with renal insufficiency showed that the metabolism of the drug is independent of kidney function, that the rate of disappearance of the unchanged glipizide was approximately the same as in norreals, but that the "halflife" of the metabolites was increased to 20 h and more.

Four subjects received 5 mg 14C-glipizide orally, 3 subjects 1 mg intravenously and 2 subjects 5 mg 14C-glibenclamide orally. Plasma levels of radioactivity, and urinary and faecal excretion were measured. For both drugs the disappearance of radioactivity from plasma followed complex kinetics and the apparent half-lives increased steadily with time. The two sulfonylureas were extensively metabolized and were excreted in the urine as hydroxylated or conjugated metabolites. The effects of both drugs on blood glucose and immunoreactive insulin were comparable. The findings are compared with other published results.

Thyrotropin releasing hormone (TRH) accelerates the turnover of phosphatrdylinosrtol m GH3 cells ('phospholiprd response') From the analysis of inositol phosphates m the presence of Li+ which inhibits their dephosphorylatron, rt can be concluded that the hydrolysis of phosphatidylmosrtol4,5-biphosphate, and possibly of phosphatidylinosrtol 4-phosphate by phospholipase C 1s markedly accelerated by TRH. It appears that this reaction initiates the acceleratron of phosphatrdylinositol turnover. The specificity of hormonally regulated phospholipase C reaction for polyphosphoinosmdes has important implications for the potential role of the phospholipid response as a mechanism of membrane signal transduction. LlthrumPhospholrpld response