| Autor: |
Ceña V; Section on Neuroendocrinology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892., Halperin JI, Yeandle S, Klein DC |
| Jazyk: |
angličtina |
| Zdroj: |
Endocrinology [Endocrinology] 1991 Jan; Vol. 128 (1), pp. 559-69. |
| DOI: |
10.1210/endo-128-1-559 |
| Abstrakt: |
Biochemical studies of K+ efflux from rat pinealocytes revealed for the first time that norepinephrine (NE) increases 86Rb+ and 42K+ efflux. The effects of NE depend upon concurrent activation of both alpha 1- and beta-adrenoceptors. This effect is mediated by cAMP and Ca2+, which appear to act in conjunction to control K+ efflux; studies with charybdotoxin and tetraethylammonium indicate that a Ca2(+)-sensitive K+ channel (K(Ca] appears to be involved. Patch clamp studies identified a large conductance (approximately 100 psec) K+ channel. This study also revealed for the first time that NE treatment increases the fraction of time that this channel was open. Studies of inside-out pineal membrane patches indicated that increasing Ca2+ at the cytoplasmic surface of the membrane increased the frequency of channel opening, as is typical of K(Ca) channels in this type of preparation. Outward K+ currents were almost completely blocked by tetraethylammonium (10 mM) and scorpion venom (L. quinquestriatum; 100 ng/ml). Cell-attached studies confirm that the effects of NE are mediated by intracellular second messengers. These investigations suggest that NE elevates K+ flux, probably through a large conductance K(Ca) channel, that NE acts through alpha 1- and beta-adrenergic receptors, and that Ca2+ and cAMP act together through a biochemical "AND" gate to mediate the effects of receptor activation. Activation of this K(Ca) channel would have a hyperpolarizing influence and might contribute to the adrenergic hyperpolarization of pinealocytes. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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