Omega-conotoxin blockade of calcium currents in cultured neonatal rat cardiomyocytes: different action on EGTA-modified calcium channels |
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Authors: | A N Savtchenko A N Verkhratsky |
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Institution: | A. A. Bogomoletz Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev, USSR. |
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Abstract: | Calcium currents from neonatal rat ventricular heart muscle cells grown in primary culture were examined using the "whole-cell" voltage clamp technique. An inward current characterized by large amplitude and slow inactivation decay was induced when the extracellular Ca2+ concentration was reduced by EGTA. This current was suppressed by extracellular Na+ removal, or by calcium antagonists, and increased by epinephrine and BAY K 8644. These findings suggest that this current is carried by sodium ions through Ca channels. Both Ca and Na currents through calcium channels were irreversibly blocked by omega-conotoxin. Complete blockade developed 10-15 minutes after the toxin introduction in the extracellular solution. Blockade of Na currents through calcium channels was characterized by a transient increase of current amplitude without any changes in its kinetics and voltage-dependent properties. Structural differences between calcium channels in rat and guinea-pig and frog cardiomyocytes were suggested. |
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