Insulin and phorbol ester stimulate conductive Na+ transport through a common pathway.

Civan, Mortimer M.; Peterson-Yantorno, K.; O’Brien, Thomas G.

doi:10.1073/pnas.85.3.963

Cited by 24 publications

(12 citation statements)

References 37 publications

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“…Insulin (and presumably GH) (58) recently showed that D-sphingosine (100 ,uM) reduces the Na+-transporting stimulation ofinsulin on frog skin, suggesting that at least part of its effects on the membrane Na+ permeability and Na+,K+-exchange pump are mediated by protein kinase C.…”

Section: Resultsmentioning

confidence: 99%

Sphingosine, an inhibitor of protein kinase C, suppresses the insulin-like effects of growth hormone in rat adipocytes.

Smal

Meyts

1989

Proc. Natl. Acad. Sci. U.S.A.

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Insulin, human growth hormone (hGH), and phorbol 12-myristate 13-acetate all stimulate lipogenesis in rat adipocytes preincubated without hGH for 4 hr. As previous data suggested that protein kinase C plays an important role in the action of insulin and in the insulin-like effects of hGH in rat adipocytes, we tested the effects of sphingosine, a potent inhibitor of protein kinase C, on the lipogenic activity of both hormones. At 50 IAM, sphingosine had no effect on basal lipogenesis but completely abolished the action of phorbol 12-myristate 13-acetate and decreased by 65% and 89%, respectively, the effects of hGH and insulin. At higher concentrations (100 ,uM), sphingosine abolished both basal and hormone-stimulated lipogenesis; this effect was partially reversible after washing the cells. Similar effects of sphingosine on basal and stimulated glucose uptake were seen in parallel, suggesting that sphingosine inhibits lipogenesis at the glucose-uptake step in rat adipocytes. N-Acetylsphingosine and sphingomyelin, two analogs of sphingosine that are inactive on protein kinase C, did not inhibit lipogenesis induced by hGH, insulin, or phorbol 12-myristate 13-acetate. Sphingosine did not inhibit insulin binding to rat adipocytes at concentrations up to 200 ,M but decreased hGH binding to its receptors by 44% at 50 ,uM. These data suggest a direct link between the inhibition ofprotein kinase C and that of lipogenesis and provide new evidence for the involvement of protein kinase C in the mechanism of action of growth hormone and insulin in rat adipocytes.Human growth hormone (hGH) exerts a variety of effects on somatic growth, development, and metabolism (1-3). While most of growth hormone (GH) effects on skeletal growth are thought to be indirect and mediated through somatomedins such as insulin-like growth factor I (2, 4), GH actions on carbohydrate and lipid metabolism are probably direct (5). GH is classically an antagonist of insulin, with lipolytic and diabetogenic effects in vivo-but paradoxically GH also exerts acute and transient insulin-like effects in vivo and in vitro in models where endogenous GH has been suppressed (1, 2, 5). We recently showed that hGH, like insulin, stimulates lipogenesis in rat adipocytes preincubated without hormones during 4 hr, and the nonadditivity of the two maximal responses strongly suggested that the two hormones share a common subset of activated pathways (6k.Despite advances in our knowledge of the mechanisms of action of GH and insulin, we still do not understand at the molecular level how these hormones transduce their signals from their specific membrane receptors into the cell. The recent cloning of a putative GH receptor (7) has provided no clue as to a possible mechanism of action. The GH receptor sequence deduced from the cDNA is not related to known tyrosine kinases or to any other known protein except the prolactin receptor (8). Foster et al. (9) reported recently that the GH receptors of 3T3-F442A fibroblasts and adipocytes are phosphorylated when occupi...

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Section: Resultsmentioning

confidence: 99%

Sphingosine, an inhibitor of protein kinase C, suppresses the insulin-like effects of growth hormone in rat adipocytes.

Smal

Meyts

1989

Proc. Natl. Acad. Sci. U.S.A.

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“…A possible basis for this mimicry of hormones by exogenous phospholipase C lies in the finding that many hormone receptors increase phospholipid turnover, production ofdiacylglycerol, and activation of the calcium-and phospholipid-dependent enzyme, protein kinase C (PKC) (2)(3)(4), and there is indirect evidence for PKC participation in acute metabolic effects of insulin on adipocytes and other cells. Tumor-promoting phorbol esters, which substitute for diacylglycerol in stimulating PKC (3), increase transport of glucose (5-9) and amino acids (7), activate pyruvate dehydrogenase (7), increase lipogenesis (6,8,(9)(10)(11), and stimulate ion transport (12,13). Moreover, insulin has been reported to increase phospholipid metabolism (14)(15)(16) and the formation of diacylglycerol in adipose tissue (17) and in cultured myocytes (17)(18)(19), but there is sharp disagreement on this issue (20,21).…”

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confidence: 99%

Insulin, oxytocin, and vasopressin stimulate protein kinase C activity in adipocyte plasma membranes.

Egan

Saltis

Wek

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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Incubation of isolated rat adipocytes with insulin, vasopressin, or oxytocin increased plasma membranebound protein kinase C (PKC) activity by 100-400%. PKC activity was assayed by a procedure that is virtually background-free, thus permitting assay of protein kinase activity in highly diluted samples of solubilized membranes. Hormonedependent increases in PKC activity were limited to plasma membranes. Stimulation of the kinase was half-maximal with 70 pM insulin, and the hormone effect was rapid. Oxytocin and vasopressin produced effects on PKC similar to insulin, but the magnitude of the vasopressin stimulation exhibited seasonal variations. Treatment of cells with phorbol 12-myristate 13-acetate (PMA) resulted in a loss of PKC activity from the cytosol and a gain in plasma membrane activity, indicative of translocation of the enzyme. With activity measurements it was not possible to determine if insulin stimulated a translocation of the kinase. However, Western blot analysis of plasma membranes with polyclonal antibodies directed against PKC suggest that at least some ofthe insulin-stimulated PKC activity resulted from enzyme translocation.hand, decreased phorbol ester binding to adipocyte plasma membrane sites, thought to represent PKC, has been observed after treatment of fat cells with insulin (27).Like phorbol esters, vasopressin and oxytocin mimic a number of insulin effects on adipocytes (for examples, see refs. 1, 28-30). However, in contrast to insulin, stimulation of phospholipid metabolism and diacylglycerol formation in adipocytes by vasopressin and oxytocin is readily detected (20,21). Moreover, PKC has been implicated in the actions of these nonapeptide hormones in a variety of cells (for examples, see refs. [31][32][33][34]. Nevertheless, other than a report on activation of hepatic PKC with vasopressin (35), there appear to be no reports that directly demonstrate increased PKC activity in isolated membranes after exposure of adipocytes or other types of cells to either vasopressin or oxytocin.In this paper, with the use of a highly sensitive protein kinase assay method (36), we report that exposure of isolated rat adipocytes to insulin, vasopressin, or oxytocin increases PKC activity in adipocyte plasma membranes.In 1966 Rodbell (1) noted that "there is some common action of oxytocin, insulin and phospholipase C," based on the observation that, when applied extracellularly, the three agents increased glucose transport and amino acid incorporation into proteins of fat cells. A possible basis for this mimicry of hormones by exogenous phospholipase C lies in the finding that many hormone receptors increase phospholipid turnover, production ofdiacylglycerol, and activation of the calcium-and phospholipid-dependent enzyme, protein kinase C (PKC) (2-4), and there is indirect evidence for PKC participation in acute metabolic effects of insulin on adipocytes and other cells. Tumor-promoting phorbol esters, which substitute for diacylglycerol in stimulating PKC (3), increase transport of glucose...

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“…The effects of insulin in vitro on epithelial Na ϩ channels appear to be tissue dependent. In amphibian model systems, insulin clearly stimulates ENaCmediated Na ϩ transport as shown in studies of frog skin (28), toad urinary bladder (3,29), and A6 cells (2,9). As discussed above, the rat CCD responds to insulin with an increase in Na-K-ATPase activity.…”

Section: Discussionmentioning

confidence: 88%

“…Insulin stimulates Na-K-ATPase in many cell types including the mammalian cortical collecting duct (CCD) (7,8). The hormone also clearly upregulates the epithelial Na channel (ENaC) in amphibian model tissues, including frog skin (28), toad urinary bladder (3,29), and A6 cells (2,9). However, such effects have not been observed in mammalian kidney tubules (15,34).…”

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confidence: 95%

Effects of insulin on Na and K transporters in the rat CCD

Frindt

Palmer

2012

American Journal of Physiology-Renal Physiology

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We tested the effects of insulin (2 nM, 30-60 min) on principal cells of isolated split-open rat cortical collecting ducts (CCD) using whole-cell current measurements. Insulin addition to the superfusate of the tubules enhanced Na pump (ouabain-sensitive) current from 18 ± 3 to 31 ± 3 pA/cell in control and from 74 ± 9 to 126 ± 11 pA/cell in high K-fed animals. It also more than doubled ROMK (tertiapin-Q-sensitive) K(+) currents in control CCD from 320 ± 40 to 700 ± 80 pA/cell, although it did not affect this current in tubules from K-loaded rats. Insulin did not induce the appearance of amiloride-sensitive Na(+) current in control animals, while in high K-fed animals the currents were similar in the presence (140 ± 30) and the absence (180 ± 70 pA/cell) of insulin. Intraperitoneal injection of insulin plus hypertonic dextrose decreased Na excretion, as previously reported. However, injection of dextrose alone, or the nonmetabolized sugar mannose, had similar effects, suggesting that they were largely the result of vascular volume depletion rather than specific actions of the hormone. In summary, we find no evidence for acute upregulation of the epithelial Na channel (ENaC) by physiological concentrations of insulin in the mammalian CCD. However, the hormone does activate both the Na/K pump and apical K(+) channels and could, under some conditions, enhance renal K(+) secretion.

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Insulin and phorbol ester stimulate conductive Na+ transport through a common pathway.

Cited by 24 publications

References 37 publications

Sphingosine, an inhibitor of protein kinase C, suppresses the insulin-like effects of growth hormone in rat adipocytes.

Sphingosine, an inhibitor of protein kinase C, suppresses the insulin-like effects of growth hormone in rat adipocytes.

Insulin, oxytocin, and vasopressin stimulate protein kinase C activity in adipocyte plasma membranes.

Effects of insulin on Na and K transporters in the rat CCD

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