Journal of Applied Physiology, Vol 71, Issue 4 1489-1495, Copyright © 1991 by American Physiological Society
Extracellular Ca2+ mobilization in potential-dependent contraction of trachealis of maturing swine
R. W. Mitchell, T. M. Murphy, E. Kelly and A. R. Leff
Department of Medicine, University of Chicago, Illinois 60637.
We studied the effect of maturation on potassium-induced parasympathetic
activation and Ca2+ entry in tracheal smooth muscle (TSM) from fifteen
2-wk-old (2ws) and sixteen 10-wk-old (10ws) male domestic farm swine.
Atropine (10(-7) M) caused inhibition of the maximal contraction elicited
by potassium to 50.3 +/- 2.6% maximum of control response (P less than
0.001) in TSM from 2ws but had no significant effect in TSM from 10ws (94.6
+/- 4.2% maximum; P = NS vs. control). Verapamil (10(-7) M) plus 10(-7) M
atropine reduced contraction elicited by potassium in both 2ws (23.7 +/-
5.8% maximum; P less than 0.001 vs. control) and 10ws (50.6 +/- 6.3%
maximum; P less than 0.001 vs. control, P less than 0.05 vs. 2ws); 10(-6)M
verapamil caused greater than 95% blockade of contraction caused by
potassium in both 2ws and 10ws. In separate studies, atropine-treated
strips were equilibrated with extracellular Ca2+ concentrations ([Ca2+]o)
ranging from normal (1X [Ca2+]o) to four times normal (4x [Ca2+]o).
Increasing [Ca2+]o increased maximal contractile response in
atropine-treated TSM strips from 68.7 +/- 3.8% maximum for 1x [Ca2+]o to
100.8 +/- 4.8% maximum for 4x [Ca2+]o (P less than 0.001) in 2ws. Neither
atropine nor [Ca2+]o affected maximal responses of TSM in 10ws (103.5 +/-
3.0% maximum for 1x [Ca2+]o; P = NS vs. control). However, in the presence
of atropine and verapamil, 4x [Ca2+]o augmented KCl-elicited contraction of
TSM from both 2ws (46.9 +/- 6.3% maximum; P less than 0.01 vs. control) and
10ws (78.6 +/- 2.3% maximum; P less than 0.005 vs. control).(ABSTRACT
TRUNCATED AT 250 WORDS)
