Basolateral membrane responses to transport modifiers in the frog skin epithelium

Schoen, Howard F.; Erlij, David

doi:10.1007/bf00581777

Cited by 15 publications

(6 citation statements)

References 25 publications

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“…Although the voltage dependence of g~, observed by us appears to contradict that assumption, it should be noted that our observations were made some 10 to 20 sec after the onset of voltage perturbation, whereas those showing positive correlations were made long after the transport rate was altered. In this regard, it is of interest to consider Schoen and Erlij's findings in the frog skin that increase in cellular current and g,, following oxytocin and insulin often precedes increase in g/, by minutes [19]. In the presence of amiloride go = g" and gc ~ g" become near equal as they approach zero, so that …”

Section: Discussionmentioning

confidence: 94%

Voltage dependence of cellular current and conductances in frog skin

Nagel¹,

García-Díaz

Essig

1988

J. Membrain Biol.

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Knowledge of the voltage dependencies of apical and basolateral conductances is important in determining the factors that regulate transcellular transport. To gain this knowledge it is necessary to distinguish between cellular and paracellular currents and conductances. This is generally done by sequentially measuring transepithelial current/voltage (It/Vt) and conductance/voltage (gt/Vt) relationships before and after the abolition of cellular sodium transport with amiloride. Often, however, there are variable time-dependent and voltage-dependent responses to voltage perturbation both in the absence and presence of amiloride, pointing to effects on the paracellular pathway. We have here investigated these phenomena systematically and found that the difficulties were significantly lessened by the use of an intermittent technique, measuring It and gt before and after brief (less than 10 sec) exposure to amiloride at each setting of Vt. I/V relationships were characterized by these means in frog skins (Rana pipiens, Northern variety, and Rana temporaria). Cellular current, Ic, decreased with hyperpolarization (larger serosa positive clamps) of Vt. Derived Ic/Vt relationships between Vt = 0 and 175 mV (serosa positive) were slightly concave upwards. Because values of cell conductance, gc, remained finite, it was possible to demonstrate reversal of Ic. Values of the reversal potential Vr averaged 156 +/- 14 (SD, n = 18) mV. Simultaneous microelectrode measurements permitted also the calculation of apical and basolateral conductances, ga and gb. The apical conductance decreased monotonically with increasing positivity of Vt (and Va). In contrast, in the range in which the basolateral conductance could be evaluated adequately (Vt less than 125 mV), gb increased with more positive values of Vt (and Vb). That is, there was an inverse relation between gb and cellular current at the quasi-steady state, 10-30 sec after the transepithelial voltage step.

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Section: Discussionmentioning

confidence: 94%

Voltage dependence of cellular current and conductances in frog skin

Nagel¹,

García-Díaz

Essig

1988

J. Membrain Biol.

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“…(i) Insulin (4) and activators of protein kinase C (17,19,22) stimulate Na+ transport across this tissue. (ii) In part, the natriferic action of insulin (12,13) and protein kinase C activation (17) is expressed by increasing apical Na+ permeability. (iii) In other cells, insulin increases diacylglycerol production by stimulating phospholipase C hydrolysis of a phosphatidylinositol glycan (24,25) and by activating de novo phosphatidic acid synthesis (26).…”

Section: Discussionmentioning

confidence: 99%

“…Insulin exerts its natriferic effect on frog skin by at least two mechanisms, a direct stimulation of the Na,K-exchange pump (10,11) and an increase in the apical Na+ permeability (12,13). The intracellular mediators are unknown.…”

mentioning

confidence: 99%

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

Civan

Peterson-Yantorno

O’Brien

1988

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

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Insulin stimulates Na+ transport across frog skin, toad urinary bladder, and the distal renal nephron. This stimulation reflects an increase in apical membrane Na+ permeability and a stimulation of the basolateral membrane Na,K-exchange pump. Considerable indirect evidence has suggested that the apical natriferic effect of insulin is mediated by activation of protein kinase C. However, no direct information has been available documenting that insulin and protein kinase C indeed share a common pathway in stimulating Na+ transport across frog skin. In the present work, we have studied the interaction of insulin and phorbol 12-myristate 13-acetate (PMA), a documented activator of protein kinase C. Preincubation of skins with 1,2-dioctanoylglycerol, another activator of protein kinase C, increases baseline Na+ transport and reduces the subsequent natriferic response to PMA. Preincubation with PMA markedly reduces the subsequent natriferic action of insulin. This effect does not appear to primarily reflect PMA-induced internalization of insulin receptors. The insulin receptors are localized on the basolateral surface of frog skin, but the application of PMA to this surface is much less effective than mucosal treatment in reducing the response to insulin. Preincubation with D-sphingosine, an inhibitor of protein kinase C, also reduces the natriferic action of insulin. The current results provide documentation that insulin and protein kinase C share a common pathway in stimulating Na+ transport across frog skin. The data are consistent with the concept that the natriferic effect of insulin on frog skin is, at least in part, mediated by activation of protein kinase C.

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“…However, recent studies from our laboratory have shown that oxytocin and cAMP also stimulate ion movements through K+-selective channels in both the apical (2) and basolateral membranes (3,4) of amphibian tight epithelia. These findings indicate that the physiologic effects of neurohypophysial hormones may involve the activation of several ionic channels.…”

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confidence: 99%

Oxytocin and cAMP stimulate monovalent cation movements through a Ca2+-sensitive, amiloride-insensitive channel in the apical membrane of toad urinary bladder.

Driessche¹,

Aelvoet²,

Erlij³

1987

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

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The effects of oxytocin and cAMP on ion transport were investigated in toad urinary bladders incubated with Ca2+-free solutions on the apical side. Under these conditions both oxytocin and cAMP markedly stimulated the movements of Na', K+, Rb+, Cs+, Li+, and NH+ through a pathway that is insensitive to amiloride. The amiloride-insensitive currents were inhibited by the addition of Ca2 , Sr2+, or Mg2+ to the apical solution. The movement of the monovalent cations was associated with a spontaneous Lorentzian component in the power spectrum of the fluctuation in short-circuit current. The plateau of the Lorentzian component was enhanced by oxytocin and cAMP and was depressed by divalent cations. Methohexital inhibited the stimulation of monovalent cation movements caused by oxytocin. These findings suggest that oxytocin and cAMP activate at least two kinds of ionic channels in the apical membrane of toad urinary bladder: the well-known amiloride-sensitive channel and an amilorideinsensitive channel that allows the movement of several monovalent cations and is blocked by Ca2+ and other divalent cations.Until quite recently it was widely thought that the effects of neurohypophysial hormones on transepithelial ion transport are due almost exclusively to the activation of an amilorideinhibitable Na+ channel in the apical membrane (1). However, recent studies from our laboratory have shown that oxytocin and cAMP also stimulate ion movements through K+-selective channels in both the apical (2) and basolateral membranes (3, 4) of amphibian tight epithelia. These findings indicate that the physiologic effects of neurohypophysial hormones may involve the activation of several ionic channels. The purpose of the present experiments was to examine the effects of oxytocin and cAMP on an ionic channel of amphibian epithelia that is detected when Ca2> is removed from the apical solution. After Ca2> removal, a Lorentzian component appears in the noise spectrum of the apical membrane of the frog skin (5). This Lorentzian component is due to the activity of a channel that is freely permeable to a large variety of monovalent cations and is not inhibited by amiloride. MATERIALS AND METHODSThe procedures followed in our laboratory have been described in detail (6). In brief, urinary bladders of the toad (Bufo marinus) were mounted with minimal edge damage in an Ussing-type chamber, which allowed continuous perfusion of both surfaces of the tissue. The membrane area exposed to the bathing solutions was 0.5 cm2. The transepi-

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Basolateral membrane responses to transport modifiers in the frog skin epithelium

Cited by 15 publications

References 25 publications

Voltage dependence of cellular current and conductances in frog skin

Voltage dependence of cellular current and conductances in frog skin

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

Oxytocin and cAMP stimulate monovalent cation movements through a Ca2+-sensitive, amiloride-insensitive channel in the apical membrane of toad urinary bladder.

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