TY - JOUR
T1 - Ouabain-sensitive Na+,K+-ATPase activity in toad brain
AU - Morris, Jennifer F.
AU - Ismail-Beigi, Faramarz
AU - Butler, Vincent P.
AU - Gati, Irith
AU - Lichtstein, David
PY - 1997/11
Y1 - 1997/11
N2 - Toads of the genus Bufo are highly resistant to the toxic effects of digitalis glycosides, and the Na+,K+-ATPase of all toad tissues studied to date has been relatively insensitive to inhibition by digitalis and related compounds. In studies of brain microsomal preparations from two toad species, Bufo magnus and Bufo viridis, inhibition of ATPase activity and displacement of [3H]ouabain from Na+,K+-ATPase occurred over broad ranges of ouabain or bufalin concentrations, consistent with the possibility that more than one Na+,K+-ATPase isoform may be present in toad brain. The data could be fitted to one- or two-site models, both of which were consistent with the presence of Na+,K+-ATPase activity with high sensitivity to ouabain and bufalin. Ki (concentration capable of producing 50% inhibition of activity) values for ouabain in the one-site model were in the 0.2 to 3.7 μM range where as Ki(i) values in the two-site model ranged from 0.085 to 0.85 μM, indicating that brain ATPase was at least three orders of magnitude more sensitive to ouabain than B. marinus bladder ATPase (Ki = 5940 μM). Ouabain was also an effective inhibitor of 86Rb+ uptake in B. marinus brain tissue slices (Ki = 3.1 μM in the one-site model; Ki(i) = 0.03 μM in the two-site model). However, the relative contribution of the high ouabain-sensitivity site to the total activity was 17% in the transport assay as compared with 63% in the Na+,K+-ATPase enzymatic assay. We conclude that a highly ouabain-sensitive Na+,K+-ATPase activity is present and functional in toad brain but that its function may be partially inhibited in vivo.
AB - Toads of the genus Bufo are highly resistant to the toxic effects of digitalis glycosides, and the Na+,K+-ATPase of all toad tissues studied to date has been relatively insensitive to inhibition by digitalis and related compounds. In studies of brain microsomal preparations from two toad species, Bufo magnus and Bufo viridis, inhibition of ATPase activity and displacement of [3H]ouabain from Na+,K+-ATPase occurred over broad ranges of ouabain or bufalin concentrations, consistent with the possibility that more than one Na+,K+-ATPase isoform may be present in toad brain. The data could be fitted to one- or two-site models, both of which were consistent with the presence of Na+,K+-ATPase activity with high sensitivity to ouabain and bufalin. Ki (concentration capable of producing 50% inhibition of activity) values for ouabain in the one-site model were in the 0.2 to 3.7 μM range where as Ki(i) values in the two-site model ranged from 0.085 to 0.85 μM, indicating that brain ATPase was at least three orders of magnitude more sensitive to ouabain than B. marinus bladder ATPase (Ki = 5940 μM). Ouabain was also an effective inhibitor of 86Rb+ uptake in B. marinus brain tissue slices (Ki = 3.1 μM in the one-site model; Ki(i) = 0.03 μM in the two-site model). However, the relative contribution of the high ouabain-sensitivity site to the total activity was 17% in the transport assay as compared with 63% in the Na+,K+-ATPase enzymatic assay. We conclude that a highly ouabain-sensitive Na+,K+-ATPase activity is present and functional in toad brain but that its function may be partially inhibited in vivo.
KW - Rb uptake
KW - [H]ouabain binding
KW - Bladder
KW - Brain
KW - Bufalin
KW - Bufo marinus
KW - Bufo viridis
KW - Microsomal ATPase
KW - Ouabain
KW - Toad
UR - http://www.scopus.com/inward/record.url?scp=0031280437&partnerID=8YFLogxK
U2 - 10.1016/S0300-9629(96)00465-3
DO - 10.1016/S0300-9629(96)00465-3
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C2 - 9406436
AN - SCOPUS:0031280437
SN - 0300-9629
VL - 118
SP - 599
EP - 606
JO - Comparative Biochemistry and Physiology - A Physiology
JF - Comparative Biochemistry and Physiology - A Physiology
IS - 3
ER -