Calcium mobilization and isometric tension in bovine tracheal smooth muscle: effects of salbutamol and histamine.
We determined if decreases in relative free intracellular calcium concentration ([Ca2+]i) caused by salbutamol, a selective beta2-adrenoreceptor agonist, were paralleled by calcium egression from the cytosol in bovine trachealis muscle strips. [Ca2+]i, or tissue-surface extracellular calcium changes (Ts[Ca2+]ext), were monitored using Fluo-3 acetoxymethylester or Fluo-3 pentaammonium salt simultaneously with isometric tension. Salbutamol (1 microM) decreased histamine-induced isometric tension from an average peak tension of 128.5 +/- 18.4 to -4.9 +/- 0.3 mN/mm2, and reduced the associated sustained increases in [Ca2+]i from 100% at peak to 20.4 +/- 7.6%. Both histamine-induced elevation in [Ca2+]i and isometric tension were reversed completely by forskolin (1 microM). In muscle strip at active resting tension, salbutamol caused a decrease (49.6 +/- 12.1%) in [Ca2+]i. Following precontraction with histamine, salbutamol caused an immediate and sustained increase in Ts[Ca2+]ext which was not seen in a Na(+)-free solution. Finally, propranolol (10 microM) blocked both increases in Ts[Ca2+]ext and muscle relaxation caused by salbutamol. These findings indicate that in bovine trachealis muscle, the effect of salbutamol to decrease [Ca2+]i and isometric tension is via a beta2-adrenoceptor, and the changes in [Ca2+]i are by an increase in calcium egression via the Na(+)/Ca2+ exchanger, and reuptake by myoplasmic stores.
Hirsh
A J
AJ
Department of Physiology, University of Alberta, Edmonton, Canada.
Benishin
C G
CG
Jones
R L
RL
Pang
P K
PK
Man
S F
SF
D000420:Albuterol / Q000494:pharmacology*; D000814:Aniline Compounds; D000818:Animals; D001993:Bronchodilator Agents / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D005576:Colforsin / Q000494:pharmacology; D004594:Electrophysiology; D005456:Fluorescent Dyes; D006632:Histamine / Q000494:pharmacology*; D007537:Isometric Contraction / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D014132:Trachea / Q000166:cytology / Q000648:ultrastructure; D014966:Xanthenes
D000814:Aniline Compounds; D001993:Bronchodilator Agents; D005456:Fluorescent Dyes; D014966:Xanthenes; D005576:Colforsin; C059715:Fluo-3; D006632:Histamine; D012964:Sodium; D000420:Albuterol; D002118:Calcium