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Effects of K+ channel blockers on inwardly and outwardly rectifying whole-cell K+ currents in sheep parotid secretory cells

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Summary

We have used whole-cell patch-clamp techniques to examine the sensitivities of the inwardly and the outwardly rectifying K+ currents in sheep parotid cells to K+ channel blockers. Extracellular tetraethylammonium (ID50 ≈ 200 μmol/liter), quinine (ID50 ≈ 100 μmol/liter), verapamil (ID50 ≈ 30 μmol/liter) and charybdotoxin (ID50 < 0.1 μmol/liter) reduced the outwardly rectifying current but had no effect on the inwardly rectifying current. Quinidine inhibited the outwardly rectifying current (ID50 ≈ 200 μmol/liter) and, at a concentration of 1 mmol/liter, reduced the inwardly rectifying current by 35%. Extracellular Ba2+ inhibited both the inwardly and outwardly rectifying K+ currents but the inwardly rectifying K+ current was more sensitive to it (ID50 ≈ 1 μmol/liter) than was the outwardly rectifying K+ current (ID50 ≈ 2 mmol/liter). Extracellular Cs+ reduced the inwardly rectifying K+ current (ID50 ≈ 100 μmol/liter) without affecting the outwardly rectifying current; 4-aminopyridine (1 or 10 mmol/liter), lidocaine (0.1 or 1 mmol/liter) and flecainide (0.01 or 0.1 mmol/liter) affected neither current. In excised outsideout patches, the addition to the bath of quinine (100 μmol/liter), quinidine (100 μmol/liter), verapamil (100 μmol/liter) or charybdotoxin (100 nmol/liter) inhibited Ca2+- and voltage-sensitive 250 pS K+ channels (BK channels), but 4-aminopyridine (1 mmol/ liter) and lidocaine (0.1 mmol/liter) did not. The pattern of blocker sensitivities is thus consistent with the hypothesis that BK channels are responsible for the outwardly rectifying whole-cell current seen in resting sheep parotid cells.

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Authors and Affiliations

  1. Department of Physiology, University of Sydney, 2006, N.S.W., Australia

    T. Ishikawa & D. I. Cook

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  1. T. Ishikawa
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  2. D. I. Cook
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This project was supported by the Australian Research Council. We thank Professor J.A. Young for his critical reading of the manuscript and Drs. N. Sangster and J. Rothwell and Mr. R. Murphy for giving us access to their sheep.

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Ishikawa, T., Cook, D.I. Effects of K+ channel blockers on inwardly and outwardly rectifying whole-cell K+ currents in sheep parotid secretory cells. J. Membarin Biol. 133, 29–41 (1993). https://doi.org/10.1007/BF00231875

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  • DOI: https://doi.org/10.1007/BF00231875

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