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.

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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.

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.