SAMMA induces premature human acrosomal loss by Ca2+ signaling dysregulation.
SAMMA is licensed for development as a contraceptive microbicide. Understanding mechanisms of its biological activity is prerequisite to designing more active second generation products. This study examined Ca(2+) involvement in SAMMA-induced premature acrosomal loss (SAL) in noncapacitated human spermatozoa. SAMMA causes acrosomal loss (AL) in a dose-dependent manner (ED(50) = 0.25 microg/mL). SAL requires extracellular Ca(2+) (ED(50) = 85 microM). SAL is inhibited by verapamil (nonspecific voltage-dependent Ca(2+) channel blocker; IC(50) = 0.4 microM), diphenylhydantoin and NiCl(2) (T-type [Ca(v)3.x] channel blockers; IC(50) 210 microM and 75 microM, respectively). Verapamil blockade of L-type (Ca(v)1.x) channels is use-dependent; activated channels are more sensitive to inhibition. However, verapamil inhibition of SAL does not increase after repeated SAMMA stimulation. SAL is unaffected by 10 microM nifedipine (selective L-type channel blocker). This contrasts to 40% inhibition (P < .001) of AL induced by 1 microM thapsigargin (Ca(2+)-ATPase inhibitor; releases intracellular Ca(2+) stores, promotes capacitative Ca(2+) entry). SAL is unaffected by 1 microM BAPTA-AM (intracellular Ca(2+) chelator), and 50 microM 2-APB (blocks InsP3 receptors and store-operated channels). This contrasts with thapsigargin-induced AL, inhibited nearly 65% by BAPTA-AM (P < .005) and 91% by 2-APB (P, .001). The results suggest that SAL is mediated by Ca(2+) entry through channels pharmacologically similar to the T-type (Ca(v)3.2) class. This process appears distinct from that caused by physiological stimuli such as progesterone or zona pellucida-derived proteins. SAMMA's contraceptive activity may be caused by induction of premature AL through dysregulation of Ca(2+) signaling.
Anderson
Robert A
RA
Department of Obstetrics and Gynecology, Rush University Medical Center, Chicago, Illinois 60612, USA. randerso@rush.edu
Feathergill
Kenneth A
KA
Waller
Donald P
DP
Zaneveld
Lourens J D
LJ
D000177:Acrosome / Q000187:drug effects*; D020101:Acrosome Reaction / Q000187:drug effects; D000328:Adult; D000890:Anti-Infective Agents / Q000009:adverse effects*; D001896:Boron Compounds / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects; D020013:Calcium Signaling / Q000187:drug effects*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008297:Male; D008333:Mandelic Acids / Q000009:adverse effects* / Q000037:antagonists & inhibitors; D009532:Nickel / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D010672:Phenytoin / Q000494:pharmacology; D011108:Polymers / Q000009:adverse effects*; D019284:Thapsigargin / Q000037:antagonists & inhibitors; D014700:Verapamil / Q000494:pharmacology
D000890:Anti-Infective Agents; D001896:Boron Compounds; D015220:Calcium Channels; D008333:Mandelic Acids; D011108:Polymers; C468727:SAMMA; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D000001:Calcimycin; D004533:Egtazic Acid; D010672:Phenytoin; D019284:Thapsigargin; C022838:nickel chloride; D009532:Nickel; D014700:Verapamil; C109986:2-aminoethoxydiphenyl borate; D009543:Nifedipine; D002118:Calcium