Divalent chelating agents, calcium blockers and metabolic inhibitors had different effects on the iris sphincter muscles
Suzuki, R.; Yoshino, H.; Kobayashi, S.
Nippon Ganka Gakkai Zasshi 90(3): 448-452
1986
ISSN/ISBN: 0029-0203 PMID: 3716941 Document Number: 276278
The iris sphincter does exhibit spontaneous activity in Ba2+ solution, without stimulation. Aqueous divalent cations Ca2+ and Mg2+ had remarkable effects on the spontaneity of the iris sphincter. In the present experiment, Ca2+ chelating- and/or Mg2+ chelating-agents (0.1-1 mM) did not reduce the amplitude of the spontaneous contraction induced by 1-2.5 mM Ba2+, and high concentrations (e.g., 2 mM) inhibited the spontaneity. Similarly, Ca2+ antagonist verapamil (10-7-106M) did not reduce the contraction, and high concentrations (10-5-10-4M) were required to inhibit the spontaneous activity. Under such a condition, electrical stimulation produced a detectable contraction. Metabolic inhibitor, fluoride Na, iodoacetic acid or ouabain abolished both the spontaneous activity and electrically stimulated contraction. The present experiment suggests that the action of Ba2+ is very different from that of Ca2+ in normal Krebs solution. Inhibition by high concentrations of chelating agents probably implies the unspecific impairment of the muscle cell membrane.