Simple and specific assessment of Ca-entry-blocking activities of drugs by measurement of Ca reversal.
A new, simple, and specific screening method for Ca-entry blocker is reported. In the presence of various blockers of Ca-entry (Ca-channel blockers), Ca2+ (1 x 10(-4) M) causes Ca reversal, i.e., it causes relaxation of rat uterine smooth muscle that has been tonically contracted with oxytocin in Ca-free medium (Ca-free contraction) after prolonged preincubation with 3 mM EGTA. The potencies of various drugs to cause Ca reversal, assessed on an all-or-none basis, were found to reflect their activities of blocking Ca entry. The potencies of drugs for blocking Ca entry via voltage-operated Ca-channels could be determined in 125.6 mM K+ Ca-free medium. Drugs that inhibited Ca-free contraction directly have some other antispasmodic activity. Conventionally, activity for blocking Ca entry is screened by measuring inhibition of Ca-induced contraction, but true Ca-entry blocking activity cannot be differentiated clearly from other antispasmodic activity when a drug has both activities. However, by measuring Ca reversal, activity for blocking Ca entry only can easily be found, when done in solution with high K+ content for blocking voltage-operated channels and when done in solution with normal K+ content for blocking voltage-independent channels.
Matsuo
K
K
Department of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Morita
S
S
Uchida
M K
MK
Sakai
K
K
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors* / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D005260:Female; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D010276:Parasympatholytics / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D014599:Uterus / Q000187:drug effects / Q000502:physiology
D002121:Calcium Channel Blockers; D010276:Parasympatholytics; D002118:Calcium