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A23187 increases calcium permeability of store sites more than of surface membranes in the rabbit mesenteric artery.
Author(s) -
Itoh T,
Kanmura Y,
Kuriyama H
Publication year - 1985
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1985.sp015597
Subject(s) - contraction (grammar) , caffeine , chemistry , procaine , calcium , egta , muscle contraction , endocrinology , medicine , biophysics , anatomy , anesthesia , biology , organic chemistry
The effects of a Ca ionophore, A23187, were investigated on intact and skinned smooth muscle tissues of the rabbit mesenteric artery. A23187 (over 10(‐9) M) inhibited, dose dependently, contractions induced by 10(‐5) M‐noradrenaline (NA) or 10 mM‐caffeine in Ca2+‐free solution containing 2 mM‐EGTA. Procaine (3 mM) led to cessation of the caffeine‐ or NA‐induced contractions in the presence or absence of Ca2+. When A23187 (10(‐7) M) was applied, the contractions in the presence of procaine were to some extent restored in Krebs solution. A23187 at a concentration of 10(‐7) M did not modify the resting muscle tone, but this concentration did increase the amplitude of the contraction evoked by 20.2 or 128 mM‐K+ and markedly inhibited the 10(‐7) M‐NA or 10 mM‐caffeine‐induced contraction in Krebs solution. A23187 (10(‐7) M) delayed the onset and rising phase of the 10(‐5) M‐NA‐induced contraction with inhibition of the oscillatory contractions. High concentrations of A23187 (over 10(‐6) M) produced a large contraction in the presence and a small contraction in the absence of 2.6 mM‐Ca2+. These A23187‐induced contractions were not inhibited by 10(‐7) M‐nisoldipine, a Ca2+ antagonist. A23187 (over 10(‐6) M) applied for a long period functionally skinned the muscle tissues. However, the Ca2+ sensitivity of the A23187‐treated skinned muscles was lower than that of saponin‐treated muscles. In saponin‐treated skinned muscles, A23187 (below 10(‐6) M) had no effect on the pCa‐tension relation. After filling the store, A23187 (over 10(‐7) M) generated a larger contraction than did caffeine in Ca2+‐free solution, in the presence or absence of 5 mM‐NaN3. When 10(‐7) M‐A23187 was applied once for 5 min, subsequently applied caffeine (20 mM), following application of Ca2+, no longer produced contraction of skinned muscle tissues. The present results indicate that low concentrations of A23187 show a selective Ca2+‐releasing action on Ca2+ store sites in muscle cells and that high concentrations increase the Ca2+ leakage (influx) and the cell membrane is skinned.