Effects of 5-hydroxytryptamine (serotonin) and forskolin on intracellular free calcium in isolated and fura-2 loaded smooth-muscle cells from the anterior byssus retractor (catch) muscle of Mytilus edulis.
Effects of 5-hydroxytryptamine (5-HT) and forskolin on intracellular free calcium concentration [( Ca2+]i) were studied in suspensions of fura-2 loaded smooth-muscle cells from the anterior byssus retractor 'catch' muscle of Mytilus edulis. The successive addition of 5 mM carbachol (CCh) and 100 mM KCl to the suspension evoked a transient elevation of [Ca2+]i from the resting value of 124 +/- 2.7 nM (mean +/- SE, n = 18) to 300-400 nM, which was associated with contraction. The change in [Ca2+]i induced CCh was concentration-dependent with the EC50 of 10(-5) M. The resting [Ca2+]i was unaffected by 10 microM 5-HT. The change in [Ca2+]i induced by 5 mM CCh was suppressed by 5-HT from 167 +/- 14.0 (n = 11) to 124 +/- 14.9 (n = 8) nM whereas that induced by 100 mM KCl was enhanced from 321 +/- 31.9 to 405 +/- 17.6 nM (n = 8). 5-HT applied during the decaying phase of the CCh response caused a rapid decline in [Ca2+]i. In both the responses to CCh and KCl, the falling phase was accelerated by 5-HT. 10 microM forskolin, a potent activator of adenylate cyclase, mimicked the effects of 5-HT as did a membrane-permeant cyclic AMP analogue, 8-parachlorophenylthio cyclic AMP (cpt-cAMP). Application of 100 microM cpt-cAMP partially suppressed the Ca2+i response to CCh and enhanced that to KCl. D-Tubocurarine (500 microM) added during the decaying phase of the response induced by 100 microM CCh, caused a rapid decline in [Ca2+]i similar to that caused by both 5-HT and forskolin.(ABSTRACT TRUNCATED AT 250 WORDS)
Ishii
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Zoological Institute, Faculty of Science, University of Tokyo, Japan.
Simpson
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AW
Ashley
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CC
D000818:Animals; D001572:Benzofurans; D049872:Bivalvia / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002469:Cell Separation; D005576:Colforsin / Q000494:pharmacology*; D005456:Fluorescent Dyes; D016257:Fura-2; D007425:Intracellular Membranes / Q000378:metabolism*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D014403:Tubocurarine / Q000494:pharmacology
D001572:Benzofurans; D005456:Fluorescent Dyes; D005576:Colforsin; D012701:Serotonin; D011189:Potassium Chloride; D002217:Carbachol; D002118:Calcium; D016257:Fura-2; D014403:Tubocurarine