Membrane effects of nucleotides and their role in the realization of transmitter actions on the heart muscle cells of Helix pomatia L.

Kiss, Tibor and S.-Rózsa, Katalin (1975) Membrane effects of nucleotides and their role in the realization of transmitter actions on the heart muscle cells of Helix pomatia L. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 42. pp. 43-60. ISSN 0365-3005

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Abstract

Studying th membrane effect of the substances relating to the second messenger system on the Helix heart, it was stated, that: 1. At the beginning of their application cAMP, DBcAMP, theophylline and imidazole increase diastolic depolarization, the duration of the plateau phase and the frequency of the spontaneous action potentials. At the second period of their action, the amplitude of the action potentials is lowered then the potential generation ceased. The intracellular site of the actions was prevailing on their effect. 2. The above substances depolarize or hyperpolarize the membrane only slightly, synchronously lowering membrane resistance. 3. The changes in the different phases of the action potentials are attributed to the decrease in K-permeability and increase in Ca-permeability. During the application of cyclic nucleotides the alterations in permeability were only secondarily appearing as a consequence of phosphorylation of the membrane components. 4. After pretreatment with cyclic nucleotides or theophylline the effect of 5HT and ACh failed to occur on the membrane of Helix heart. The common application of 5HT with cyclic nucleotides decreased while theophylline increased th e resistance of th e surface membrane, but in the presence of ACh both the cyclic nucleotides and theophylline caused a decrease in membrane resistance. The changes in membrane effects of the transmitter can be explained by prolonged alterations of permeability caused by cyclic nucleotides.

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