Summary
CaCl2, K-EGTA or Ca-EGTA were injected into shortened Purkinje fibres in order to modify the concentration of ionized calcium ([Ca2+]i). Two injection techniques were used: A method of microiontophoresis between two intracellular microelectrodes and a method of pressure injection using heating in a closed system.
Continuous microiontophoresis of CaCl2 at a rate of 10−13 Mol/s, caused shortening of the action potential, enhancement of the afterpotential, and hyperpolarisation of the resting potential within 1 s. This response was steady within about 10 s and disappeared in less than 1 s when injection was ended. Pressure injection of small volumes of 1 M CaCl2 evoked the same response. Injection of KCl was ineffective.
When K-EGTA was injected the action potential became longer and the afterpotential was suppressed. After 2 min of continuous injection the fibres depolarized to about −40 mV. The effect of K-EGTA injection was fully reversible but recovery required several minutes.
Injection of Ca-EGTA buffer solutions evoked (initially) a response similar to that described for CaCl2 injection provided that [Ca2+]i was greater than 5·10−7 M. Conversely, when [Ca2+]i was equal to or less than 1·10−7 M an EGTA-like response could be seen.
The results favour (but do not prove) the idea that [Ca2+]i mediates the observed effects via an influence on the potassium conductance.
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Supported by SFB 38, Membranforschung, project G2
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Isenberg, G. Cardiac Purkinje fibres. Pflugers Arch. 371, 51–59 (1977). https://doi.org/10.1007/BF00580772
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DOI: https://doi.org/10.1007/BF00580772