Stimulation by cGMP of apical Na channels and cation channels in toad urinary bladder

S. Das, M. Garepapaghi and L. G. Palmer Department of Physiology, Cornell University Medical College, New York, New York 10021. The effects of 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) on apical membrane cation conductances in the toad urinary bladder were investigated. 8-BrcG...

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Veröffentlicht in:American Journal of Physiology: Cell Physiology 1991-02, Vol.260 (2), p.C234-C241
Hauptverfasser: Das, S, Garepapaghi, M, Palmer, L. G
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Sprache:eng
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Zusammenfassung:S. Das, M. Garepapaghi and L. G. Palmer Department of Physiology, Cornell University Medical College, New York, New York 10021. The effects of 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) on apical membrane cation conductances in the toad urinary bladder were investigated. 8-BrcGMP (1 mM) added to the serosal solution increased the amiloride-sensitive short-circuit current (INa) after a delay of 5 min to a steady-state value 1.8 times that of controls achieved after 30 min. Similar effects were seen when the bladders were bathed on the serosal side with a normal NaCl Ringer solution and with a high-K sucrose solution to depolarize the basolateral membrane. Under the latter conditions, the amiloride-sensitive transepithelial conductance increased in parallel with the short-circuit current, indicating stimulation of apical membrane Na channels. The threshold concentration for observing the stimulation of INa was 100 microM, 10-100 times larger than the concentration of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) required to elicit an increase in INa. Currents through an outwardly rectifying Ca-sensitive cation conductance (Iout) were also increased by 1.8-fold relative to controls. This stimulatory effect occurred after a delay of 15 min and reached maximal levels 90-120 min after addition of the nucleotide. The effects of cGMP on INa were not additive with those of 8-BrcAMP or with antidiuretic hormone, an agent known to act by increasing cAMP within the cell. Addition of 1 mM 3-isobutyl-1-methylxanthine to the serosal side of the bladders stimulated INa by 1.3-fold and Iout by 2.4-fold. In both cases, subsequent addition of cGMP produced no further activation of either conductance.
ISSN:0363-6143
0002-9513
1522-1563
DOI:10.1152/ajpcell.1991.260.2.c234