Adrenergically activated Ca2+ increases in brown fat cells: effects of Ca2+, K+, and K channel block.
We measured intracellular calcium concentration ([Ca2+]i) during adrenergic stimulation using fura-2 ratio imaging of individual cultured neonatal rat brown fat cells. One micromolar norepinephrine (NE) increased [Ca2+]i from an average resting value of 105 nM to 555 nM in approximately 30 s. [Ca2+]i remained elevated as long as NE was present but returned to resting levels within 2-3 min after NE removal. The response was half maximal at approximately 50 nM NE and was primarily alpha-adrenergic. The sustained, but not the initial, increase in [Ca2+]i required extracellular calcium. Cells stimulated in high-K media had [Ca2+]i responses like those in 0 Ca2+, suggesting that depolarization abrogates calcium influx. Parallel perforated-patch recordings showed that the increase in [Ca2+]i activates a calcium-activated K conductance. Blocking K channels with moderate concentrations of tetraethylammonium (TEA) had only small effects on NE-induced changes in [Ca2+]i, but high concentrations of TEA significantly reduced the response. We conclude that cytoplasmic calcium is modulated by fluxes from both intracellular and extracellular sources and that K channels may not be required for normal short-term [Ca2+]i responses to hormone.
Lee
S C
SC
Department of Animal Physiology, University of California, Davis 95616.
Nuccitelli
R
R
Pappone
P A
PA
D002001:Adipose Tissue, Brown / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002478:Cells, Cultured; D005110:Extracellular Space / Q000378:metabolism; D016257:Fura-2; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D012996:Solutions; D013566:Sympathomimetics / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D012996:Solutions; D013566:Sympathomimetics; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D011188:Potassium; D002118:Calcium; D016257:Fura-2