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Inward calcium current in twitch muscle fibres of the frog.
Author(s) -
Sanchez J A,
Stefani E
Publication year - 1978
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1978.sp012496
Subject(s) - calcium , chemistry , tetraethylammonium , biophysics , tetrodotoxin , potassium , voltage clamp , sartorius muscle , sodium , contraction (grammar) , anatomy , membrane potential , endocrinology , biochemistry , biology , organic chemistry
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.