Coordinated Action of Calcium Ion and Adenosine 3′,5′-Monophosphate upon the Release of α-Melanocyte-Stimulating Hormone from the Intermediate Lobe of the Rat Pituitary Gland

Tsuruta, K.; Grewe, C. W.; Côté, Thomas E.; Eskay, Robert L.; Kebabian, John W.

doi:10.1210/endo-110-4-1133

Cited by 38 publications

(20 citation statements)

References 26 publications

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“…This has been confirmed by the experiments of Lee (1996), and by the results shown in Figs 1 and 2. In rat melanotrophs cAMP alone, in the absence of Ca¥, probably cannot affect the release process (Tsuruta et al 1982), and similar findings have been reported in bovine pituitary lactotrophs (Sikdar, Zorec & Mason, 1990). It has been shown previously that stimulation of intact pituitary cells by dbcAMP causes phosphorylation of specific proteins in intact pituitary cells (Brattin & Portanova, 1981).…”

Section: Discussionsupporting

confidence: 80%

“…In previous studies the co-ordinated action of Ca¥ and cAMP on the release of á-MSH from the intermediate lobe of the rat pituitary gland has been suggested (Tsuruta et al 1982), such that cAMP in some way enhances the effects of Ca¥ upon the release process. This has been confirmed by the experiments of Lee (1996), and by the results shown in Figs 1 and 2.…”

Section: Discussionmentioning

confidence: 98%

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Modulation of the unitary exocytic event amplitude by cAMP in rat melanotrophs

Sikdar

Kreft

Zorec

1998

The Journal of Physiology

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Secretory responses were measured in single rat pituitary melanotrophs as the relative increase in membrane capacitance (Cm) 8 min after the start of dialysis with solutions containing 0.45 μm Ca2+. In the added presence of cAMP (0.2 mM) in the patch pipette solution, capacitance responses increased 2‐ to 3‐fold in comparison with controls. To study whether cAMP‐dependent mechanisms affect cytosolic calcium activity ([Ca2+]i), dibutyryl cyclic AMP (dbcAMP, 10 mM) was added to intact melanotrophs and [Ca2+]i was measured using fura‐2 AM. Addition of dbcAMP caused a transient reduction in [Ca2+]i to 82 ± 21 nM from a resting value of 100 ± 19 nM (mean ± s.e.m., n= 32, P < 0.002), indicating that the cAMP‐induced increase in secretory activity was not the result of cAMP acting to increase [Ca2+]i, which then increased secretory activity. To investigate whether cAMP affects the secretory apparatus directly, the interaction of a single secretory granule with the plasmalemma was monitored by measuring discrete femtofarad steps in Cm. The signal‐to‐noise ratio of recordings was increased by pre‐incubating the cells with a hydrophobic anion, dipicrylamine. Recordings of unitary exocytic events (discrete ‘on’ steps in Cm) showed that the amplitude of ‘on’ steps ‐ a parameter correlated to the size of exocytosing secretory granules ‐ increased from 4.2 ± 0.2 fF (n= 356) in controls to 7.9 ± 0.2 fF in the presence of cAMP (n= 329, P < 0.001), while the frequency of unitary exocytic events was similar in controls and in the presence of cAMP. The results suggest that a cAMP‐dependent mechanism mediates the fusion of larger granules with the plasmalemma.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 98%

Modulation of the unitary exocytic event amplitude by cAMP in rat melanotrophs

Sikdar

Kreft

Zorec

1998

The Journal of Physiology

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“…In the former the amount of hormone released is small, whereas responses to Ba show that release of much larger amounts can be achieved and sustained. Moreover, Ca itself, when introduced to melanotrophs by the ionophore A23187, elicits a more persistent secretary response (Tsuruta et al 1982). All this supports our earlier interpretation that Ca current through the voltage-dependent Ca channels of melanotrophs rapidly inactivates on depolarization (Tomiko et al 1981).…”

Section: Differential Inactivation Of Responsiveness To Ca and Ba By supporting

confidence: 82%

“…This allows the action of Ba to be interpreted within the framework of the general Ca hypothesis of stimulus-secretion coupling (Douglas, 1968) in which Ca-activated exocytosis figures as a central common element in diverse cell types (for a recent review see Rubin, 1982). The scheme is applicable to melanotrophs since MSH secretion is inhibited by procedures that suppress Ca entry (Tomiko et al 1981;Tsuruta, Grewe, Cote, Eskay & Kebabian, 1982) and stimulated by Ca in the presence of the ionophore A23187 (Tsuruta et al 1982), and since these cells are depolarized by excess K, possess voltage-dependent Ca-channels blocked by Co , 1980 and secrete MSH in response to excess K in a Ca-dependent and Co-blockable manner (Tomiko et al 1981). Indeed this pattern indicates that melanotrophs belong to that subclass of secretary cells in which stimulus-secretion coupling is effected by inward Ca current through voltage-dependent Ca channels (Douglas, 1978).…”

Section: Ba Is Effective After Responsiveness To Ca Is Inactivatedmentioning

confidence: 99%

Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.

Douglas¹,

Taraskevich²,

Tomiko³

1983

The Journal of Physiology

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Ba ions caused an intense and prolonged discharge of melanocyte‐stimulating hormone (MSH) from perifused neurointermediate lobes of mouse pituitaries and dispersed pars intermedia cells. The effect persisted in chronically cultured lobes or cells. It did not require Ca, but, like the Ca‐dependent response to excess K, was blocked by cyanide combined with glucose lack. The secretagogue effect of Ba was blocked or prevented by Co or by excess Ca, both of which can reduce inward Ba currents through Ca channels. Prior exposure to excess K partially reduced the secretagogue effect of Ba, suggesting that depolarization caused some inactivation of Ba current. In contrast to Ba, excess K elicited secretion that was transient, and prior exposure of preparations to excess K (in the absence of Ca) profoundly suppressed the secretagogue effect of Ca. The evidence is consistent with the view that inward Ca current rapidly inactivates in these cells. It is concluded that Ba ions have a potent and persistent direct secretagogue effect on the melanotrophs that may reflect, in part, their ability to penetrate Ca channels more easily than Ca ions. The strong secretagogue effects of Ba on melanotrophs may be of considerable utility in studies on MSH secretion since a physiological secretagogue has yet to be discovered. Moreover, since the responses of melanotrophs (and other endocrine cells) to Ba can be distinguished from those of various other secretory cells and neurones, it is suggested that Ba may provide a tool for characterizing the distinctive membrane properties of the Ba‐responsive endocrine cells.

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“…2A). Second, cholera toxin increases the formation of cAMP by intact rat IL cells [7,33,34] (fig. 3A).…”

Section: (I-adrenoceptormentioning

confidence: 99%

Biochemical and Physiological Studies of the Beta-Adrenoceptor and the D-2 Dopamine Receptor in the Intermediate Lobe of the Rat Pituitary Gland: A Review

Côté¹,

Eskay²,

Frey³

et al. 1982

Neuroendocrinology

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136

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The intermediate lobe (IL) of the rat pituitary gland responds to catecholamines. Catecholamines interacting with the β-adrenoceptor stimulate adenylate cyclase activity, enhance cyclic AMP formation and thereby trigger the release of α-melanocyte-stimulating hormone (α-MSH). Catecholamines interacting with a D-2 dopamine receptor (in the classification schema of Kebabian and Calne) diminish adenylate cyclase activity and thereby decrease the capacity of IL cells to synthesize cyclic AMP. Dopaminergic agonists also inhibit the release of α-MSH from IL cells. The homogeneity of the IL facilitates biochemical investigations of this tissue.

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Coordinated Action of Calcium Ion and Adenosine 3′,5′-Monophosphate upon the Release of α-Melanocyte-Stimulating Hormone from the Intermediate Lobe of the Rat Pituitary Gland

Cited by 38 publications

References 26 publications

Modulation of the unitary exocytic event amplitude by cAMP in rat melanotrophs

Modulation of the unitary exocytic event amplitude by cAMP in rat melanotrophs

Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.

Biochemical and Physiological Studies of the Beta-Adrenoceptor and the D-2 Dopamine Receptor in the Intermediate Lobe of the Rat Pituitary Gland: A Review

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