Ionic currents in slow twitch skeletal muscle in the XXXX .

@entity2227 @entity1022 @entity1372 @entity969 @entity2865 @entity35
1. The ionic currents in slow fibres isolated from @entity35 soleus muscle have been studied under voltage-clamp conditions with a double @entity969 -gap method and the results are compared to those obtained from fast fibres isolated from the iliacus muscle. 2. The mean value of the resting potential in slow fibres is -70 mV. a value 8 mV more positive that the mean resting potential of fast fibres (-78 mV). 3. In slow muscle, a fast inward current which is blocked by @entity1022 and which depends on external @entity1372 concentration is presumed to be carried by @entity1372 ions. The characteristics of this current, which are time- and voltage-dependent, are similar to those of the iliacus fibres. From a holding potential at -86 mV, this inward current is maximal (2.6 mA/cm2 +/- 0.3) at +49.1 mV +/- 1.5 (mean +/- S.E. of mean), reverses at +127.3 mV +/- 2.2 (mean +/- S.E. of mean), and its half inactivation occurs at +23.2 mV +/- 0.8 (mean +/- S.E. of mean). 4. The delayed outward current in slow fibres is unchanged by exposure to @entity2865 free solution and has a time course very different from that found in fast fibres. This current reaches an initial peak in 5-10 msec and a second peak or steady level after 40-150 msec. The decay of the outward current is also very different, being ten times slower than that in fast fibres (1500-3000 msec). 5. Analysis of the tail currents reveals the existence of two components of delayed current in slow fibres. The faster component reverses at a potential of 11.3 mV +/- 0.9 (mean +/- S.E. of mean) positive to the holding potential (equivalent to a membrane potential of about -75 mV), in contrast to a reversal potential of 35.4 mV +/- 2.5 (mean +/- S.E. of mean) positive to the holding potential for the slower component (equivalent to a membrane potential of about -51 mV. 6. In L- @entity2227 solution the characteristics of the inward-going rectification are the same in the two types of muscle.
