Premium
Effects of the calcium channel facilitator, CGP 28,392, on different modes of contraction in smooth muscle of rabbit and rat aortae and guinea‐pig taenia caeci
Author(s) -
Karaki H.,
Nagase H.,
Ozaki H.,
Urakawa N.,
Weiss G.B.
Publication year - 1986
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1986.tb10276.x
Subject(s) - verapamil , contraction (grammar) , medicine , endocrinology , taenia coli , aorta , histamine , guinea pig , vascular smooth muscle , muscle contraction , chemistry , calcium , biology , anatomy , smooth muscle
1 Effects of a Ca 2+ channel facilitator, CGP 28,392, on smooth muscle contractions were examined in order to delineate characteristics of Ca 2+ channels in rabbit and rat aortae and guinea‐pig taenia caeci. 2 Application of increasing concentrations of KCl induced contractile responses in these smooth muscles and CGP 28,392 shifted the concentration‐response curve for KCl to the left. The maximum response was also increased in rat aorta and guinea‐pig taenia. CGP 28,392 also shifted the concentration‐response curves for noradrenaline in rat aorta and for histamine in taenia to the left and increased the maximum response in rat aorta. However, the corresponding curve for noradrenaline in rabbit aorta was not affected by CGP 28,392. 3 The sustained contractions induced by KCl were inhibited by cumulative application of verapamil in these smooth muscles. Pretreatment of the muscle with CGP 28,392 decreased the inhibitory effect of verapamil. The noradrenaline‐induced contraction in rat aorta and the histamine‐induced contraction in taenia were also inhibited by verapamil, and CGP 28,392 antagonized the effect of verapamil. The noradrenaline‐induced contraction in rabbit aorta was only slightly inhibited by verapamil, and CGP 28,392 did not modify the effect of verapamil. 4 In these smooth muscles, cumulative application of Ca 2+ to the Ca 2+ ‐depleted, KCl‐treated muscle induced contraction, and the concentration‐response curve for Ca 2+ was shifted to the left by CGP 28,392 and to the right by verapamil. The concentration‐response curves for Ca 2+ in Ca 2+ ‐depleted, noradrenaline‐treated rabbit and rat aortae and in Ca 2+ ‐depleted, histamine‐treated taenia were also shifted to the left by CGP 28,392 and to the right by verapamil. In some contractions, CGP 28,392 increased and verapamil decreased the maximum responses. CGP 28,392 antagonized the inhibitory effect of verapamil. 5 These results suggest that the Ca 2+ channel facilitator, CGP 28,392, has a relatively selective activating effect on voltage‐dependent Ca 2+ channels in rabbit aorta. However, it also activates receptor‐linked Ca 2+ channels in rabbit aorta when Ca 2+ concentrations are low. In rat aorta and guinea‐pig taenia this facilitator activates both types of Ca 2+ channels.