Inward calcium current in twitch muscle fibres of the frog.
1. Voltage clamp experiments using the three micro-electrode voltage clamp technique were performed on sartorius muscles of the frog. 2. By blocking potassium currents with tetraethylammonium and replacing chloride ions with sulphate a slow inward current was detected. 3. The slow inward current is mainly carried by calcium, since it is abolished by cobalt and D-600, it depends on external calcium, and is not affected by removing external sodium or by tetrodotoxin (TTX). 4. The slow inward current has a mean threshold of -40 mV, reaches a mean maximum value at ca. 0 mV of 81 microamperemetercm-2 and has a mean reversal potential of +38 mV. 5. The calcium current is inactivated by the application of 2 sec conditioning prepulses according to a sigmoid curve with V(h) = -42 mV and k = 6.2 mV. 6. The slow time course of this calcium current makes it rather unlikely that it participates in contraction during a twitch, but it might be activated during long depolarizations as potassium contractures.
D000200:Action Potentials; D000818:Animals; D001001:Anura; D002118:Calcium / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology; D004553:Electric Conductivity; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000502:physiology*; D011894:Rana pipiens; D012964:Sodium / Q000494:pharmacology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D013757:Tetraethylammonium Compounds; D005711:Gallopamil; D003035:Cobalt; D013779:Tetrodotoxin; D012964:Sodium; D002118:Calcium