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Ionic effects on amiloride block of the mechanosensitive channel in Xenopus oocytes
Author(s) -
Lane John W.,
McBride Don W.,
Hamill Owen P.
Publication year - 1993
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1993.tb13449.x
Subject(s) - amiloride , xenopus , potency , mechanosensitive channels , biophysics , patch clamp , epithelial sodium channel , chemistry , ion channel , sodium channel , voltage clamp , endocrinology , pharmacology , sodium , membrane potential , biochemistry , biology , receptor , in vitro , organic chemistry , gene
1 Patch clamp techniques were used to measure the ionic dependence of amiloride block of single mechanosensitive (MS) channels in frog ( Xenopus laevis ) oocytes. 2 The primary aim was to determine whether the difference in potency of amiloride block of MS channels in frog oocytes (IC 50 = 0.5 m m ) and chick auditory hair cells (IC 50 = 50 μ m ) was due to the different ionic recording solutions. 3 Amiloride block of the oocyte MS channel does not vary significantly with complete substitution of external Na + (i.e. 100 m m ) with K + in Ca 2+ ‐free recording solution (in both Na + and K + the IC 50 = 0.5 m m ). 4 A physiological concentration (1.8 m m ) of external Ca 2+ blocks the oocyte MS channel and reduces the potency of amiloride block (IC 50 = 1.1 m m ) without altering the voltage‐dependence or the Hill coefficient ( n = 1.8) of amiloride block. The reduction in potency can be explained by surface charge screening by Ca 2+ which reduces the effective amiloride surface concentration. 5 The present results indicate that factors other than ionic recording conditions must underlie the difference in potency of amiloride block of MS channels in oocytes and auditory hair cells.