Comparative effects of divalent cations on the methylmercury (MeHg)-induced alterations of acetylcholine (ACh) release
Bath application of MeHg at the neuromuscular junction increases spontaneous release of ACh while blocking evoked release of ACh, effects observed electrophysiologically as increased miniature end-plate potential frequency (MEPP/sub f/) and cessation of end-plate potentials (EPPs), respectively. The objectives of the present study were to test (1) whether the effect of MeHg on MEPP/sub f/ was Ca/sup 2 +/-specific by substituting Sr/sup 2 +/ or Ba/sup 2 +/ for Ca/sup 2 +/ and (2) whether the time course of MeHg-induced block of EPPs was altered by varying Ca/sup 2 +/ concentrations or substituting Sr/sup 2 +/. MEPP/sub f/ was recorded continuously from the rat hemidiaphragm using conventional methods during pretreatment with 2 mM Ca/sup 2 +/, 2 mM Sr/sup 2 +/ or 0.5 mM Ba/sup 2 +/ and subsequently with the cation plus 100 ..mu..M MeHg. MeHg elicited virtually identical increases in MEPP/sub f/ under all conditions. However, the increased MEPP/sub f/ occurred more rapidly in Sr/sup 2 +/ solutions than Ca/sup 2 +/ or Ba/sup 2 +/ solutions. EPs were recorded from the rat hemidiaphragm cut muscle preparation during pretreatment with either 2, 4, or 8 mM Ca/sup 2 +/ or 2 or 4 mM Sr/sup 2 +/ and subsequently with the cation plus 100 ..mu..M MeHg. Under all conditions EPP amplitude remained unchanged from pretreatment values until block occurred after 8-9 min exposure to MeHg. Thus, the effects of MeHg on spontaneous and nerve-evoked ACh release are not Ca/sup 2 +/-specific; MeHg produces identical effects when cations which substitute for Ca/sup 2 +/ in the release process are present.
- Research Organization:
- Michigan State Univ., East Lansing
- OSTI ID:
- 6926819
- Report Number(s):
- CONF-8604222-
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 45:4; Conference: 70. annual meeting of the Federation of American Society for Experimental Biology, St. Louis, MO, USA, 13 Apr 1986
- Country of Publication:
- United States
- Language:
- English
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ACETYLCHOLINE
SECRETION
METHYLMERCURY
BIOLOGICAL EFFECTS
MUSCLES
ELECTROPHYSIOLOGY
BARIUM COMPOUNDS
CALCIUM COMPOUNDS
CATIONS
COMPARATIVE EVALUATIONS
NERVES
RATS
STRONTIUM COMPOUNDS
VALENCE
ALKALINE EARTH METAL COMPOUNDS
AMINES
AMMONIUM COMPOUNDS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
CHARGED PARTICLES
DRUGS
ESTERS
IONS
MAMMALS
MERCURY COMPOUNDS
NERVOUS SYSTEM
NEUROREGULATORS
ORGANIC COMPOUNDS
ORGANIC MERCURY COMPOUNDS
PARASYMPATHOMIMETICS
PHYSIOLOGY
QUATERNARY COMPOUNDS
RODENTS
VERTEBRATES
560300* - Chemicals Metabolism & Toxicology