High selectivity of calcium channels in single dialysed heart cells of the guinea‐pig.
- 31 August 1984
- journal article
- research article
- Published by Wiley in The Journal of Physiology
- Vol. 354 (1), 253-272
- https://doi.org/10.1113/jphysiol.1984.sp015374
Abstract
Membrane currents and action potentials were recorded in single ventricular cells obtained from guinea-pig hearts by enzymatic dissociation. Ca2+ channel currents carried by Ba2+ or Ca2+ were recorded with a suction pipette (5-10 .mu.m diameter) for voltage clamp and internal dialysis. Currents through Na+, K+ and non-selective monovalent cation channels were suppressed by suitable holding potentials and external and internal solutions. The dialysis method allowed exchange within minutes of alkali metal cations (e.g., Cs+) and small molecules (e.g., quaternary derivatives of lidocaine and verapamil). Ca2+ channels remained functional for considerable periods, typically 20 min and sometimes more than 1 h. With Ba2+ outside and Cs+ inside, current flow through Ca2+ channels changed from inward to outward at strongly positive levels beyond a clear-cut reversal potential Erev. Several methods for defining Erev were in close agreement: zero-crossing of leak-subtracted peak current, inversion of time-dependent current changes during channel activation or inactivation, inversion of drug-sensitive current as defined by channel blockers such as Cd2+ or D-600. Erev varied with external Ba2+ or internal Cs+. Erev increased by 29 mV 10-fold increase in Ba2+. Interpreted with constant-field theory, Erev values correspond to PBa/PCs of .apprx. 1360. With 5 mM-Ca2+ outside and 151 mM-Cs+ inside, Ca2+ channel current reversed near + 75 mV corresponding to PCa/PCs .apprx. 6000. Earlier measurements of Erev suggest the PCa/PK > 1000. At strongly positive membrane potentials where channel activation is maximal, the Ca2+ channel current-voltage relationship is strongly non-linear, with conductance increasing on either side of an inflexion point near Erev. Activation of inward or outward currents through Ca2+ channels follows a sigmoid time course, as expected if activation were a multi-step process.This publication has 37 references indexed in Scilit:
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