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Calcium block of guinea‐pig heart sodium channels with and without modification by the piperazinylindole DPI 201‐106.
Author(s) -
Nilius B
Publication year - 1988
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1988.sp017095
Subject(s) - conductance , pipette , chemistry , patch clamp , sodium , analytical chemistry (journal) , sodium channel , biophysics , chromatography , biochemistry , physics , biology , receptor , organic chemistry , condensed matter physics
1. External Ca2+ block of Na+ channels was studied by a gigaohm‐seal patch clamp technique in single cardiac ventricular cells from guinea‐pig. Single‐channel currents were recorded from cell‐attached patches. 2. Increasing external Ca2+ concentrations in the patch pipette from 0.1 to 20 mM reduced the single‐channel conductance of normal Na+ channels from 27 to 14 pS without causing flickering (obtained from linear regression, eight patches). 3. Exposed to external Ca2+ concentrations of 20 mM, the single‐channel currents decreased at potentials negative to ‐60 mV in spite of an increased driving force for inward Na+ currents. 4. An external concentration of 35 mM‐Mg2+, which is supposed to exert a screening of surface charges nearly equal to that of 20 mM‐Ca2+ (Hille, Woodhull & Shapiro, 1975), reduced the single‐Na+‐channel conductance only from 26 (1 mM‐Mg2+) to 20 pS (linear regression, eight patches). A weaker voltage‐dependent block at potentials negative to ‐50 mV was observed in 35 mM‐Mg2+ than in 20 mM‐Ca2+. Therefore, surface charge effects cannot explain the obvious reduction of the conductance of single Na+ channels found when the external Ca2+ concentration was increased. 5. Single Na+‐channel currents increased with an increase in the external Na+ concentration [( Na+]o) but showed saturation. The Na+o‐single‐channel current relationship could be described by i = imax/(1 + kd/[Na+]o) with imax = 5.4 pA and kd = 359 mM (seventeen patches). 6. The mean open time of Na+ channels varied between 0.18 and 0.59 ms (potentials between ‐80 and ‐20 mV). No significant changes in the mean open time could be obtained when Ca2+ was varied between 0.1 and 20 mM. 7. The piperazinylindole compound DPI 201‐106 was used as a tool to prolong the open time of single Na+ channels. If the external Ca2+ concentration was increased from 0.1 to 20 mM the currents through the modified channels were reduced. The reduction of single‐channel currents was accentuated at potentials negative to ‐60 mV (20 mM‐Ca2+) similar to the control channels. 8. In contrast to non‐modified Na+ channels, the mean open time of DPI 201‐106‐modified channels proved extremely voltage and Ca2+ dependent.(ABSTRACT TRUNCATED AT 400 WORDS)