Effects of cadmium on Na+ transport in the isolated skin of the toad Pleurodema thaul.
Cadmium ions applied to either (outer or inner) surface of the isolated toad skin dose-dependently increased the short-circuit current (SCC), the potential difference (V) and the active sodium conductance (G(Na)) in the concentration range 0.07-0.50mM. Maximal stimulatory effect was over 30% with an EC(50) of about 0.1mM. The effect of the highest concentration used (0.75mM) decreased considerably, and when it was applied to the inner surface (10 experiments), induced between 30% and 40% inhibition of the electric parameters in four experiments. Pretreatment with amiloride inverted the stimulatory effect of externally applied Cd(2+), suggesting competitive action on the apical Na(+) channel. The effect of noradrenaline (NA) was increased after outer application of Cd(2+) and decreased after inner application of the metal: the latter effect might be due to cadmium inhibition of the activity of Na(+),K(+)-ATPase. On the other hand, pretreatment with amiloride was followed by partial although transient reversal of its effects by serosal Cd(2+), which might be explained by action of cadmium on cytoplasmic lysine residues concerned with Na(+) channel gating. The amiloride test showed that the increment of the electric parameters was due principally to stimulation of the driving potential for Na(+) (V-E(Na(+))) and that inhibition was accompanied by a reduction in the V-E(Na(+)) and by a significant decrease in skin resistance indicating possible disruption of membrane or cell integrity. These data are in favor of the possibility that externally applied Cd(2+) activates toad skin ion transport, partly by increasing apical sodium conductance and also by stimulating the V-E(Na(+)), and that internally applied Cd(2+), with easier access to membrane and cellular constituents, may inhibit the sodium pump.
Suwalsky
M
M
Department of Polymers, Faculty of Chemical Sciences, University of Concepción, E. Larenas 129, Casilla 160-C, Concepción, Chile. msuwalsk@udec.cl
Norris
B
B
Cárdenas
H
H
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001001:Anura; D002104:Cadmium / Q000633:toxicity*; D004785:Environmental Pollutants / Q000633:toxicity; D005260:Female; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D012867:Skin / Q000187:drug effects* / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology
D004785:Environmental Pollutants; D026941:Sodium Channel Blockers; D002104:Cadmium; D000584:Amiloride; D012964:Sodium; D009638:Norepinephrine