Omega-conotoxin blockade of calcium currents in cultured neonatal rat cardiomyocytes: different action on EGTA-modified calcium channels.
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.
Savtchenko
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A. A. Bogomoletz Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev, USSR.
Verkhratsky
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D000818:Animals; D000831:Animals, Newborn; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology*; D006321:Heart / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D010456:Peptides, Cyclic / Q000494:pharmacology*; D051381:Rats; D015222:Sodium Channels / Q000502:physiology; D016276:Ventricular Function; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010456:Peptides, Cyclic; D015222:Sodium Channels; D020960:omega-Conotoxins; C053423:Conus magus toxin; D004533:Egtazic Acid