| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1. Helix aspersa neurones under voltage clamp generate prolonged outward currents (potassium currents) in response to depolarizing command pulses. 2. The potassium currents recorded from cell A were reversibly reduced 25-50% by 10 mM cobalt ions in the bathing medium; 1 mM lanthanum, 10(-6) g/ml. D-600 and 10(-6) g/ml. iproveratril had similar effects but were only partially reversible. 3. The relationship between the potassium currents and the membrane potential had an "n" shape in normal saline. In calcium-free saline (containing 25 mM magnesium) the potassium currents were reduced and the "n" shape was abolished. The effect of calcium-free saline was readily reversible. 4. The voltage-dependence of the calcium-sensitive potassium currents was similar to that of the "late" calcium channel in squid axons (Baker, Hodgkin & Ridgway, 1971). 5. When cell A was depolarents were made up of two exponentially declining components. The slower of the two components was reduced in calcium-free saline. 6. When cell A was depolarized by 150 mV for 10 msec and then repolarized the "tail" currents were made up of a single rapidly declining component. The reversal potential of this component changed by 58 mV for a tenfold change in the external potassium concentration as predicted by the Nernst equation. 7. The reversal potential of "tail" currents having both components was less sensitive to changes in the external potassium concentration. 8. Tetraethylammonium (TEA) ions blocked both calcium dependent and voltage sensitive potassium currents. Each receptor was found to bind a single molecule of TEA. The dissociaton constant was about 10 mM in each case. 9. The intracellular concentration of ionized calcium was estimated from the potential at which there was no apparent calcium influx (the null point). It was between 3 x 10(-8) M and 8 x 10(-8) M with 10(-2) M calcium in the bathing medium. 10. The null point changed 30 mV for a tenfold change in the external calcium concentration as predicted by the Nernst equation. 11. It is concluded that depolarization of Helix neurones activates two typesof potassium channel. One channel is voltage dependent and highly selective for potassium. Activation of the other channel is dependent on the influx (or injection, see Meech, 1972, 1974a) of calcium. This calcium mediated potassium activation system saturates at high external calcium concentrations and is inhibited by external magnesium ions.
This article has been cited by other articles:
|
|
 |
|
  W. T. Clusin Mechanisms of calcium transient and action potential alternans in cardiac cells and tissues Am J Physiol Heart Circ Physiol, January 1, 2008; 294(1): H1 - H10. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. S. Denton, F. V. McCann, and J. C. Leiter CO2 chemosensitivity in Helix aspersa: three potassium currents mediate pH-sensitive neuronal spike timing Am J Physiol Cell Physiol, January 1, 2007; 292(1): C292 - C304. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Matsumoto, T. Tanimoto, S. Yoshida, M. Ikeda, M. Takeda, C. Saiki, Y. Shimazu, T. Aoba, M. Nasu, and K. Suzuki Effects of Acetazolamide and 4-Aminopyridine on CO2-induced Slowly Adapting Pulmonary Stretch Receptor Inhibition in Rats Chem Senses, May 1, 2004; 29(4): 351 - 361. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Matsumoto, M. Ikeda, T. Nishikawa, S. Yoshida, T. Tanimoto, M. Ito, C. Saiki, and M. Takeda Excitatory Mechanism of Deflationary Slowly Adapting Pulmonary Stretch Receptors in the Rat Lung J. Pharmacol. Exp. Ther., February 1, 2002; 300(2): 597 - 604. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Yu, G. N. Gamkrelidze, P. J. Laurienti, and J. E. Blankenship Serotonin Directly Increases a Calcium Current in Swim Motoneurons of Aplysia brasiliana Integr. Comp. Biol., August 1, 2001; 41(4): 1009 - 1025. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Zufall, T. Leinders-Zufall, and C. A. Greer Amplification of Odor-Induced Ca2+ Transients by Store-Operated Ca2+ Release and Its Role in Olfactory Signal Transduction J Neurophysiol, January 1, 2000; 83(1): 501 - 512. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Matsumoto, T. Takahashi, T. Tanimoto, C. Saiki, and M. Takeda Effects of Potassium Channel Blockers on CO2-Induced Slowly Adapting Pulmonary Stretch Receptor Inhibition J. Pharmacol. Exp. Ther., September 1, 1999; 290(3): 974 - 979. [Abstract] [Full Text]
|
|
|
|
|
|
A. Chrachri and R. Williamson Voltage-Dependent Conductances in Cephalopod Primary Sensory Hair Cells J Neurophysiol, December 1, 1997; 78(6): 3125 - 3132. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Meis and H.-C. Pape Properties of a Ca2+-Activated K+ Conductance in Acutely Isolated Pyramidal-Like Neurons From the Rat Basolateral Amygdaloid Complex J Neurophysiol, September 1, 1997; 78(3): 1256 - 1262. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Subramony and S. E. Dryer Neuregulins stimulate the functional expression of Ca2+-activated K+ channels in developing chicken parasympathetic neurons PNAS, May 27, 1997; 94(11): 5934 - 5938. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
