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Regulation of Intracellular Calcium in Brown Adipocytes
-
- Zhang, Shi-Jin, 1957- (författare)
- Stockholms universitet
-
- Wang, Lawrence C.H, Professor (opponent)
- University of Alberta, Kanada
- (creator_code:org_t)
- ISBN 9171538763
- Stockholm : Stockholm University, 1999
- Engelska 70 s.
- Doktorsavhandling (övrigt vetenskapligt/konstnärligt)
Abstract
Ämnesord
Stäng
- Intracellular Ca2+ is considered a primary regulator of cell function. In the present study, the control and the effects of intracellular Ca2+ in brown adipocytes have been investigated. Cytosolic Ca2+ levels ([Ca2+]i) are the resultant of the activity of Ca2+ transport systems. Results concerning Ca2+transport systems in the plasma membrane, endoplasmic reticulum and mitochondria are presented.[Ca2+]i, monitored with Fura-2/AM, is increased when brown adipocytes are stimulated with norepinephrine (NE). The NE effect is mediated via a1-adrenoceptors and involves both release from intracellular Ca2+ stores and influx of extracellular Ca2+. The NE-induced [Ca2+]i response could be desensitized by pretreatment with NE. The desensitization is also mediated by a1-receptors and intracellularly by increased [Ca2+]i and calmodulin but not by protein kinase C. The kinetics of the desensitization are similar to those of inhibition of protein synthesis or transcription and the desensitization is associated with a comparable decrease in the number of a1-receptors.Mitochondrial Ca2+ levels ([Ca2+]m) were monitored within brown adipocytes with mitochondrially targeted aequorin. [Ca2+]m was not a simple reflection of [Ca2+]i; rather, evidence is presented for the existence of a b-adrenergic, cAMP-mediated signal that augments the [Ca2+]m/[Ca2+]i ratio. This signal causes the mitochondria to sequester Ca2+ even in the absence of increased cytosolic levels. Inhibition of mitochondrial Ca2+ uptake augments the cytosolic responses. Mitochondria may thus play an important role even in cytosolic Ca2+homeostasis in brown adipocytes.Chronic treatment of brown adipocytes with NE resulted in marked alterations of cytosolic Ca2+ handling, but the mitochondria retained their ability to sequester Ca2+during adrenergic stimulation, i.e. under conditions when UCP1 should be active.The effects of an increase in [Ca2+]i involve activation of a cAMP phosphodiesterase, and the presence of this component explains the unusual kinetic characteristics of norepinephrine-induced cAMP accumulation. [Ca2+]i is also involved in the regulation of gene expression: increased [Ca2+]i interacts synergistically with cAMP in the control of c-fos expression which may be of significance for regulation of cell proliferation and differentiation.It was concluded that Ca2+ is a primary regulator of physiological functions in brown adipocytes. The Ca2+ transport systems in brown adipocytes are involved in the regulation of intracellular and intraorganellar Ca2+. Changes of the free cytosolic Ca2+ concentration by hormone stimulation induces the activation of many physiological processes.
Ämnesord
- NATURVETENSKAP -- Biologi -- Zoologi (hsv//swe)
- NATURAL SCIENCES -- Biological Sciences -- Zoology (hsv//eng)
Nyckelord
- zoofysiologi
- Zoological physiology
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- dok (ämneskategori)
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