Single-channel properties of cloned cGMP-activated channels from retinal rods

M. Nizzari, F. Sesti, M. T. Giraudo, C. Virginio, A. Cattaneo, V. Torre

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34 Scopus citations


Single-channel properties of a cloned channel activated by cyclic GMP have been analysed. The mRNA encoding for the channel was injected into oocytes of Xenopus laevis and the current flowing through a single ionic channel activated by cGMP was studied in excised patches under voltage-clamp conditions. The ionic channel activated by cGMP had a single-channel conductance of 32 ± 2 pS at + 120 mV and 25 ± 4 pS at -120 mV, and its conductance was not significantly affected by increasing the cGMP concentration from 20 μM to 200 μM. The single-channel currents in the presence of NH4+, Na+, K+, Li+ and Rb+ in the medium bathing the cytoplasmic side of the membrane at + 140 mV were 5.3, 4.7, 3.8, 1.3 and 0.8 pA, respectively. The single-channel current in the presence of Cs+ was less than 0.5 pA. Ca2+ and Mg2+ (both 0.5 mM) in the presence of 100 μM cGMP did not appreciably affect the channel activity at membrane potentials more negative than -80 mV, whereas at + 100 mV they reduced the single-channel conductance by about threefold. The ionic selectivity and the blockage by divalent cations of the native channel found in amphibian rods and in the cloned channel from bovine rods are quite similar. However, the cloned channel has well-resolved openings, especially at positive membrane voltages, whereas the native channel is characterized by a continuous flickering between the open and closed state.

Original languageEnglish (US)
Pages (from-to)69-74
Number of pages6
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1339
StatePublished - 1993
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Immunology and Microbiology
  • General Biochemistry, Genetics and Molecular Biology
  • General Environmental Science
  • General Agricultural and Biological Sciences


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