| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Biological Sciences, University of Southern California, Los Angeles, CA 90007, U.S.A.
Department of Physiology, Ahmanson Laboratory-B.R.I., and Jerry Lewis Neuromuscular Research Center, University of California, Los Angeles, CA 90024, U.S.A.
1. When K+ is removed from both sides of the somal membrane of Limnea neurones, time-dependent, voltage-dependent outward currents are observed at positive potentials. These currents can be carried by Tris+ and tetraethylammonium (TEA+), as well as Cs+, but the Cs currents are several times larger. The Cs currents are not affected by external or internal TEA, but are strongly reduced by 4-aminopyridine (4-AP) and all Ca blockers tried.
2. The presence of these non-specific outward currents and their sensitivity to all treatments that eliminate the Ca currents prevent the complete isolation of Ca currents. The non-specific outward currents are most prominent at large positive potentials and as slow tail currents on stepping back to the holding potential.
3. Ca currents are `washed out' in well perfused cells. Typically the Ca current has decayed to less than one tenth of its original size after 
h of perfusion. This wash-out is specific for the Ca current; Na and K currents persist for several hours.
4. Once the Ca current has completely decayed, it is possible to study one type of non-specific current without overlapping inward currents. This current activates between 0 and +30 mV and appears to reverse near 0 mV.
5. In spite of the probable presence of slowly activating outward currents, the net inward currents measured show little apparent inactivation. In all the cells studied the inward current evoked at +20 mV has never decayed by more than 50% during a 60 ms pulse. So the true inactivation of these Ca currents must be quite slow, with time constants of the order of 100 ms and larger.
6. The activation of the Ca current agrees with m2 kinetics. The rate of activation is the same for Ba currents as for Ca currents.
7. When the membrane potential is stepped back to the holding level (-50 mV), the Ca current turns off quite rapidly with a time constant of about 100 µs (25 °C). The time constant for turning off the Ca current is not related to the time constant for turning on the Ca current at the same voltage as expected for m2 kinetics in the Hodgkin and Huxley model. At -30 mV the 
m for turn-on is eight times larger than the m for turn-off.
This article has been cited by other articles:
|
|
 |
|
  T. E. Decoursey Voltage-Gated Proton Channels and Other Proton Transfer Pathways Physiol Rev, April 1, 2003; 83(2): 475 - 579. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. M. Henderson and R. W. Meech Proton Conduction through gp91phox J. Gen. Physiol., November 25, 2002; 120(6): 759 - 765. [Full Text] [PDF]
|
|
|
|
 |
|
 C. Thaler, W. Li, and P. Brehm Calcium Channel Isoforms Underlying Synaptic Transmission at Embryonic Xenopus Neuromuscular Junctions J. Neurosci., January 15, 2001; 21(2): 412 - 422. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. D. Mills and R. M. Pitman Electrical Properties of a Cockroach Motor Neuron Soma Depend on Different Characteristics of Individual Ca Components J Neurophysiol, November 1, 1997; 78(5): 2455 - 2466. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. J. Hong and G. A. Lnenicka Characterization of a P-Type Calcium Current in a Crayfish Motoneuron and Its Selective Modulation by Impulse Activity J Neurophysiol, January 1, 1997; 77(1): 76 - 85. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
