ZINC IS AN INHIBITOR OF THE STIMULATORY RESPONSE OF THE SODIUM-EFFLUXTO THE MICROINJECTION OF CYCLIC-AMP AND FORSKOLIN IN SINGLE BARNACLE MUSCLE-FIBERS

The main aim of the experiments with which this paper deals was to tes t the hypothesis that Zn is an inhibitor of the stimulatory response o f the ouabain-insensitive component of the Na efflux to the injection of cAMP, DcAMP (dibutyryl-cAMP) and FD (forskolin derivative) in barna cle muscle fibers. The results obtained were as follows: (1) External application of Zn caused a fall in the Na efflux in fibers poisoned wi th ouabain beforehand; (2) external application of Zn prior to the inj ection of cAMP, DcAMP and FD led to a marked reduction in the response of the Na efflux in fibers pre-treated with ouabain; (3) the response obtained by the injection of DcAMP and FD into ouabain-poisoned fiber s pre-exposed to Zn was small but sustained; and (4) external applicat ion of Zn following peak stimulation by injecting DcAMP or FD led to r eversal of this response. (Parallel experiments involving the injectio n of cAMP were not done, since the response following the onset of pea k stimulation decays quite rapidly.) Taken together, these results sup port the hypothesis that Zn behaves as an inhibitor of the stimulatory response obtained by the injection of cAMP, DcAMP and FD.