Differential effects of mercurial and methylmercurial ions on the phrenic nerve and diaphragm of the mouse.
Both Hg2+ and CH3Hg+ exert a depressive action on the twitch amplitude elicited by nerve stimulations more rapidly than that by muscle stimulation. CH3Hg+ was relatively more potent than Hg2+ in the nerve depressive action but was weaker on the muscle. Hg2+ induced a rapid phase and a slow phase of contracture in the diaphragm, while CH3Hg+ induced only a slow one. The biphasic contracture induced by Hg2+ could be inhibited by repetitive washout of the diaphragm with low Ca2+ (10(-3) mM) Krebs and also by treatment with glycerol to close T-tubule, while the slow contracture induced by CH3Hg+ was little affected by glycerol treatment. None of denervation, d-tubocurarine and tetrodotoxin inhibited the contracture induced by Hg2+ and CH3Hg+, indicating that the contracture was induced by a direct action on the muscle. Hg2+, but not CH3Hg+, rapidly caused a decrease of the membrane potential, decreased the amplitude and prolonged the duration of the muscle action potential. Hg2+ also initially decreased and then increased 45Ca2+ uptake of the diaphragm, but CH3Hg+ had no effect, except a prolonged incubation at a high concentration. The action of Hg2+ could be antagonized by glutathione, and CH3Hg+ was more susceptible than Hg2+ to the antagonistic action of glutathione. Both Hg2+ and CH3Hg+ did not change the ATP content of the diaphragm. All of these findings indicate that the monovalent organic CH3Hg+, with a higher lipophilicity, possesses a higher affinity to the nerve while the divalent cationic Hg2+ exerted more effects than CH3Hg+ on the sarcolemma of the mouse diaphragm.
Fu
W M
WM
Pharmacological Institute, College of Medicine, National Taiwan University, Taipei, R.O.C.
Liu
C Y
CY
Lin-Shiau
S Y
SY
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D003964:Diaphragm / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D005260:Female; D005990:Glycerol / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008628:Mercury / Q000494:pharmacology*; D008767:Methylmercury Compounds / Q000494:pharmacology*; D051379:Mice; D008813:Mice, Inbred ICR; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects; D010791:Phrenic Nerve / Q000187:drug effects* / Q000378:metabolism; D012132:Respiratory Muscles / Q000187:drug effects* / Q000378:metabolism
D002132:Calcium Radioisotopes; D008767:Methylmercury Compounds; D000255:Adenosine Triphosphate; D008628:Mercury; D005990:Glycerol; D002118:Calcium