Organic Ca(2+)-antagonist-resistant response to FMRF-NH2 on the molluscan smooth muscle.
1. FMRF-amide (10(-7)-10(-5) M) contracted molluscan anterior byssus retractor muscle in a concentration-dependent fashion. 2. The concentration-response curve of FMRF-amide was shifted rightward by an analogue of FMRF-amide, FMRf-amide ([D-Phe4]FMRF-amide, putative FMRF-amide receptor antagonist) in a parallel manner (pA2 = 4.87 +/- 0.04). 3. Although a contractile response to KCl was reduced by the organic Ca2+ antagonists (verapamil, diltiazem and high concentration of nifedipine and nicardipine). FMRF-amide-induced contraction was not markedly reduced by them. 4. In the Ca(2+)-free medium, FMRF-amide-induced contraction was diminished. The response was also reduced by TMB-8 (10(-4) M), suggesting that FMRF-amide-induced contraction might be partly dependent on intracellular Ca2+. 5. An inorganic Ca(2+)-antagonist, MnCl2, markedly reduced the FMRF-amide- and KCl-induced contraction. The results show that FMRF-amide-induced contraction might be dependent on extracellular Ca2+. 6. These findings suggest that FMRF-amide-induced contraction might be mediated through an action on FMRF-amide receptors and not through the activation of organic Ca2+ antagonist-sensitive Ca2+ channels.
Kizawa
Y
Y
Department of Physiology and Anatomy, Nihon University College of Pharmacy, Chiba, Japan.
Inudoh
S
S
Arai
Y
Y
Uemura
Y
Y
Ohura
M
M
Matsuura
R
R
Tsukimura
T
T
Murakami
H
H
D000818:Animals; D049872:Bivalvia / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002712:Chlorides; D004110:Diltiazem / Q000494:pharmacology; D019835:FMRFamide; D066298:In Vitro Techniques; D008345:Manganese / Q000494:pharmacology; D017895:Manganese Compounds; D009130:Muscle, Smooth / Q000187:drug effects*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002712:Chlorides; D017895:Manganese Compounds; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D008345:Manganese; D019835:FMRFamide; D011189:Potassium Chloride; D014700:Verapamil; D004110:Diltiazem; C025340:manganese chloride; D002118:Calcium