Increased inhibitory effect of phorbol ester on cytosolic Ca2+ level and contraction in rat myometrium after gestation.
Activation of voltage-dependent Ca2+ channels by high K+ (40 mM) increased the cytosolic Ca2+ level ([Ca2+]i) (estimated by fura-PE3 fluorescence ratio) and force in myometrium isolated from pregnant (21 days after gestation) and non-pregnant (estrus) rats. 12-Deoxyphorbol 13-isobutyrate (DPB, 1 mM) decreased the high (K+)-stimulated [Ca2+]i and force in a concentration-dependent manner. The inhibitory effect was stronger in the pregnant myometrium than in the non-pregnant myometrium. In the pregnant myometrium, the increase in Ca2+ permeability by ionomycin (1 microM) greatly increased [Ca2+]i and force, which were only partially inhibited by verapamil (10 microM). DPB (1 microM) inhibited the verapamil-insensitive component of the increases in [Ca2+]i and muscle tension. Oxytocin (100 nM) and thapsigargin (1 microM) also induced a verapamil-insensitive increase in [Ca2+]i and force, and DPB (1 microM) inhibited these increments. Ca2+ sensitivity of contractile elements, estimated from the relationships between Ca2+ and muscle force in intact and alpha-toxin permeabilized muscle, was not significantly changed by DPB (1 microM). In summary, DPB inhibits the increase in [Ca2+]i more strongly in myometrium isolated from pregnant rats than that from non-pregnant rats without any change in the [Ca2+]i/tension relationship. Since DPB decreased [Ca2+]i-rise induced by three different mechanisms, DPB may activate Ca2+ extrusion, rather than to inhibit a specific influx pathway, to decrease [Ca2+]i.
Department of Veterinary Pharmacology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Japan.
B K
BK
Kim
H
H
Ozaki
M
M
Hori
H
H
Karaki
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009215:Myometrium / Q000187:drug effects* / Q000378:metabolism; D010121:Oxytocin / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology*; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D010703:Phorbol Esters; C039067:12-deoxyphorbol 13-isobutyrate; D010121:Oxytocin; D014700:Verapamil; D002118:Calcium