Na, K ATPase activity during early postnatal development of the rat submandibular gland

The activity of the ouabain-sensitive Na, K ATPase was measured in membrane fractions of the submandibular gland of 1-, 7-, 14- and 21-day-old rats. This activity increased with age and reached adult levels by 21 days.     

42K spaces in submandibular gland of early postnatal rats: effects of carbachol and transport inhibitors

Summary Equivalent spaces of⁴²K were measured in fragments of the submandibular gland of 1-, 7-, 14- and 21-day-old and adult rats in the absence and presence of carbachol and the transport inhibitors ouabain and furosemide. The results indicate that the⁴²K space was increased by carbachol in an ouabain-sensitive manner at all ages studied and that part of the secretagogue-stimulated K uptake occurred by way of a furosemide-sensitive transport system in the latter part of the postnatal period and in the adult.     

Differential effects of prostaglandins and isoproterenol on cAMP content and Na,K pump activity in rat submandibular acini

Summary The -adrenergic agonist isoproterenol and prostaglandins E₁ and E₂ (but not F₂) increased the cAMP content of rat submandibular acini in vitro, but only isoproterenol enhanced ouabain-sensitive⁸⁶Rb (K) uptake. These findings suggest that cAMP is not involved in the activation of the Na, K pump in salivary cells.     

Inhibition of sarcolemmal Na,K, Mg ATPase from the guinea pig heart is not compatible with a homogeneous population of non-interacting ouabain receptors

Summary The inhibition of sarcolemmal Na, K, Mg ATPase from the guinea pig heart by ouabain was evaluated with a coupled enzyme assay. Models of negative cooperativity and of two independent receptors fitted the inhibition data equally well. The analysis was not compatible with a homogeneous population of non-interacting ouabain receptors.Acknowledgments. The technical assistance of P. Mayr and G. Ruhland is gratefully acknowledged.     

A molecular recognition hypothesis for nonpeptides: Na+ K+ ATPase and endogenous digitalis-like peptides

The molecular recognition hypothesis for peptides is that binding sites of ligands and their receptors are encoded by short, complementary segments of DNA. A corollary hypothesis for nonpeptide ligands posited here is that peptide replicas may be encoded by the DNA segment complementary to the receptor binding sites for nonpeptides. This corollary was tested for digitalis, a family of cardiotonic and natriuretic steroids including ouabain. A hexapeptide (ouabain-like peptide, OLP) complementary to a ouabain binding site on sodium/potassium dependent adenosine triphosphatase (Na⁺ K⁺ ATPase) exhibited activity in a digitalis bioassay. Antisera to the complementary peptide (OLP) stained the neurohypophysis in an immunocytochemical procedure. The complementary peptide was found to share an identical 4-amino acid region with the 39-amino acid glycopeptide moiety of the vasopressin-neurophysin precursor. This glycopeptide was isolated from pituitary extracts; it exhibited digitalis-like activity in the submicromolar range and cross-reacted with complementary peptide antibodies. Another digitalis-like substance with high activity also was detected in the extracts. These results demonstrate that the vasopressin-neurophysin glycopeptide has digitalis-like activity. Moreover, the findings are consistent with the hypothesis that peptide mimetics of nonpeptides are encoded in the genome. Received 23 November 1998; received after revision 18 January 1999; accepted 19 February 1999     

42K spaces in submandibular gland of early postnatal rats: effects of carbachol and transport inhibitors

Equivalent spaces of 42K were measured in fragments of the submandibular gland of 1-, 7-, 14- and 21-day-old and adult rats in the absence and presence of carbachol and the transport inhibitors ouabain and furosemide. The results indicate that the 42K space was increased by carbachol in an ouabain-sensitive manner at all ages studied and that part of the secretagogue-stimulated K uptake occurred by way of a furosemide-sensitive transport system in the latter part of the postnatal period and in the adult.     

Differential effects of prostaglandins and isoproterenol on cAMP content and Na, K pump activity in rat submandibular acini

The beta-adrenergic agonist isoproterenol and prostaglandins E1 and E2 (but not F2 alpha) increased the cAMP content of rat submandibular acini in vitro, but only isoproterenol enhanced ouabain-sensitive 86Rb (K) uptake. These findings suggest that cAMP is not involved in the activation of the Na, K pump in salivary cells.     

Splenic thymidine kinase and DNA during early postnatal development of the androgenized female rat

Administration of a pharmacologic dose of testosterone propionate to neonatal female rats had no effect on either thymidine kinase activity or DNA synthesis in the spleen during the first 3 postnatal weeks.     

Uptake of dopamine by the neural lobe of the pituitary gland during postnatal development of the rat

Zusammenfassung Die Aufnahme von injiziertem Dopamin wurde mit Hilfe der Fluorescenzmikroskopie in der neurosecretorischen Axone und in den Pituizyten des Hypophysenhinterlappens der Ratte nachgewiesen. Die Intensität der Fluorescenz nahm während der postnatalischen Entwicklung ab. Mögliche Erklärungen über diese Erscheinung wurden diskutiert.     

The Na/K pump,resting potential and selective permeability in canine Purkinje fibres at physiologic and room temperatures

All mammalian cells maintain a resting potential generated by ions moving down concentration gradients. In excitable cells, the inside potential is negative relative to outside. In order to maintain this electrochemical gradient, the sodium potassium (Na/K) pump actively transports out three sodium ions for every two potassium ions it brings in. This process generates a net outward current and thus hyperpolaizes the resting potential. I employed dihydroouabain (DHO) to inhibit the Na/K pump and thus measure its contribution to the resting potential. It contributed 9.0 mV at 34°C and 3.8 mV at 25°C. The P_K/P_Na ratios were calculated at both temperatures before and after subtracting the Na/K pump contribution. These ratios also suggested a decreased contribution of the Na/K pump under hypothermia. Taken together, these results suggest that the pump contribution to the resting potential is more significant at physiologic temperatures (34°C) than at room temperature (25°C), and that estimates of selective permeability can only be accurately obtained after assessing and eliminating the Na/K pump contribution to the resting potential.     

Failure of calcium to stimulate Na,K-ATPase in the presence of EDTA

Summary The effect of calcium on Na, K-ATPase activity of rat brain homogenates and its modification by the chelating agent EDTA has been investigated. In the absence of EDTA, free calcium (approximately 10^–6mol/l) stimulates Na,K-ATPase activity; in the presence of EDTA the same concentration of free calcium is without effect on the enzyme. In the absence of EDTA the stimulation by calcium of Na,-K-ATPase activity is enhanced by the additional presence of calmodulin but in the presence of EDTA, even when calmodulin is added to excess, calcium still fails to stimulate the enzyme. The possibility that EDTA interferes with an interaction between a calcium-calmodulin complex and Na,K-ATPase is discussed.The expert technical assistance of Mrs Paula Jarvie is gratefully acknowledged. Thanks are due also to Professor Philip Kuchel for assistance with the calculations to determine the concentrations of metal-ligand complexes in the experimental media.     

Kinetic arguments for the existence of a single form of intestinal ornithine decarboxylase during the postnatal development of normal and sparse-fur mutant mice and after EGF treatment

Summary The K_m for ornithine is remarkably constant during the course of postnatal development in both normal and spf mutant mice even if a large but transient increase in ornithine decarboxylase (ODC) activity is noted. Four hours after EGF injection (4 g/g b.wt) to 17-day-old normal and spf mice, a marked stimulation of ODC activity is observed but K_m remains unaffected. These data argue against the existence of multiple forms of ODC in the intestinal mucosa of mice.Supported by grant MA-8923 from the Medical Research Council of Canada. The author is Chercheur-boursier du Fonds de la Recherche en Santé du Québec.     

Differential changes in Cu,Zn and Mn superoxide dismutase activity in developing rat brain and liver

Summary The aim of our study was to assess the pattern of copper and zinc-containing superoxide dismutase (Cu, ZnSOD) and manganese-containing superoxide dismutase (MnSOD) activity from embryonic life to senescence in rat brain and liver. The two isoenzymes showed different profiles in the two organs examined. In particular, the cerebral MnSOD activity profile suggests a primary role during differentiation of this enzymatic form.     

The effect of a phorbol ester upon the cholinergic regulation of potassium permeability in the rat submandibular gland

Acetylcholine releases calcium from cytoplasmic stores and permits an influx of calcium in salivary acinar cells. The resultant rise in [Ca²⁺]_i causes an increase in potassium permeability which is an important part of the secretory response. We have investigated the effects of 12-0-tetradecanoyl phorbol-13-acetate, a potent activator of protein kinase C, upon this regulation of potassium permeability in superfused pieces of rat submandibular salivary gland. This compound inhibited the initial [Ca²⁺]_o-independent component of the response of acetylcholine but had no effect upon the subsequent [Ca²⁺]_o-dependent phase. This compound does not, therefore, appear to inhibit receptor-regulated calcium influx.     

Effect of mycotoxin (T-2 toxin) on catecholamine and Na+, K+-ATPase levels in rat epididymis

Summary The effect of mycotoxin (T-2 toxin) on catecholamines and Na⁺, K⁺-ATPase activities in rat epididymis has been evaluated. Dopamine and norepinephrine levels were significantly elevated in the caput and corpus regions whereas their levels remained unchanged in the caudal part of the epididymis. Na⁺, K⁺-ATPase activity was significantly increased in all the three regions of rat epididymis as a result of the toxin treatment. These changes may suggest an adverse effect on epididymal functions in rats.     

The effect of a bradykinin antagonist on vasodilator responses with particular reference to the submandibular gland of the cat

Summary A bradykinin analogue, D-Arg[Hyp³, Thi^{5, 8}, D-Phe⁷]-Bk, antagonized the vasodilator effect of bradykinin injected close-arterially in the submandibular salivary gland of the cat, without affecting that due to acetylcholine or nerve stimulation. The same analogue also antagonized the hypotensive response to bradykinin injected intravenously in cats and rabbits. We conclude that functional hyperaemia in the submandibular gland of the cat is not due to the release of bradykinin by salivary kallikrein.