Isoproterenol increases peripheral [Ca2+]i and decreases inner [Ca2+]i in single airway smooth muscle cells

Am J Physiol. 1995 Mar;268(3 Pt 1):C771-9. doi: 10.1152/ajpcell.1995.268.3.C771.


The effects of isoproterenol (Iso) or photolysis of caged adenosine 3',5'-cyclic monophosphate (cAMP) on intracellular Ca2+ concentration ([Ca2+]i) were studied in single airway smooth muscle cells. Changes in [Ca2+]i were measured ratiometrically. In cells loaded with 10 microM fura 2-acetoxymethyl ester (AM), superfusion of Iso (10 microM) increased [Ca2+]i in 20 of 22 cells from 153.2 +/- 21.3 to 252.8 +/- 38.3 nM, and this increase depended on extracellular Ca2+ and was blocked by ryanodine (50 microM). Photolysis of intracellular caged cAMP increased [Ca2+]i by 104.0 +/- 17.3 nM in 20 cells and decreased [Ca2+]i by 49.3 +/- 9.4 nM in 10 cells. With modified confocal microscopy, peripheral [Ca2+]i was increased and inner cytosolic [Ca2+]i was decreased during stimulation with Iso. Iso-induced decreases in [Ca2+]i were also observed with conventional optics in cells loaded with 0.5 microM fura 2-AM. However, in these same cells, Iso increased [Ca2+]i in the presence of low concentrations of ryanodine (1-20 microM). We concluded that Iso decreased [Ca2+]i in the inner cytosol but increased [Ca2+]i in the peripheral cytosol by mechanisms that depended on both extracellular and sarcoplasmic reticulum Ca2+ release channels. Our study suggests that fluorescence from a peripheral cytosol with high [Ca2+]i can sometimes confound the measurement of "cytosolic" [Ca2+]i with conventional optics.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Cattle
  • Cyclic AMP / chemistry
  • Cyclic AMP / physiology*
  • Cytosol / metabolism
  • Fluorescent Dyes
  • Fura-2
  • Isoproterenol / pharmacology*
  • Manganese / pharmacology
  • Microscopy, Fluorescence
  • Muscle, Smooth / drug effects
  • Muscle, Smooth / metabolism*
  • Photolysis
  • Ryanodine / pharmacology
  • Spectrometry, Fluorescence
  • Trachea / drug effects
  • Trachea / metabolism*


  • Fluorescent Dyes
  • Ryanodine
  • Manganese
  • Cyclic AMP
  • Isoproterenol
  • Calcium
  • Fura-2