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The effects of stimulation rate on calcium‐dependent action potentials recorded from chick embryo heart cell aggregates.
Author(s) -
Mackenzie E,
Standen N B
Publication year - 1982
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.1982.sp014096
Subject(s) - stimulation , embryo , calcium , heart cells , biophysics , medicine , chemistry , action (physics) , heart rate , microbiology and biotechnology , endocrinology , biology , myocyte , physics , quantum mechanics , blood pressure
1. Action potentials were recorded from aggregates of heart cells prepared from 3‐ to 7‐day chick embryos. At 3 days the maximum rate of rise (+ Vmax) was insensitive to TTX; at 7 days it was considerably reduced by TTX. 2. In the presence of TTX the action potential overshoot was dependent on [Ca]0; the results may be fitted using constant field theory and assuming that the membrane is over a hundred times more permeable to Ca than to Na or K. 3. An increase in stimulation rate in the range 0.2‐2 Hz led to an increase in both overshoot and + Vmax. This effect was not seen after addition of 20 mM‐tetraethylammonium ions, nor when Sr was substituted for Ca in the external medium. We suggest that these rate‐dependent changes may result from partial inactivation of an outward K current.