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Fast decrease of the peak current carried by barium ions through calcium channels in the somatic membrane of mollusc
Pflugers Archiv : European Journal of Physiology
|May 1, 1985
Summary
Barium ions rapidly reduce calcium channel current in snail neurons, suggesting two distinct channel types exist. One type is sensitive to cyclic adenosine monophosphate (cAMP) and is reversibly inhibited by barium.
Area of Science:
- Neuroscience
- Cell Physiology
- Ion Channel Function
Background:
- Potential-dependent calcium channels are crucial for neuronal function.
- Divalent cations play a significant role in modulating ion channel activity.
- Cyclic adenosine monophosphate (cAMP) is known to regulate calcium channel function.
Purpose of the Study:
- To investigate the effects of substituting external divalent cations, specifically barium (Ba), for calcium (Ca) on the function of potential-dependent Ca channels.
- To characterize the behavior of Ba currents and compare them to Ca currents under various conditions.
Main Methods:
- Experiments utilized intracellularly perfused, nonidentified snail neurons.
- External Ca was replaced with Ba to study its effects on inward currents.
- Currents were activated from holding potentials near resting potential.
- Effects of membrane hyperpolarization and intracellular cAMP were assessed.
Main Results:
- Barium substitution for calcium caused a rapid decline in peak inward current amplitude (half-times of 2-3 min).
- This decline was reversible upon membrane hyperpolarization.
- The steady-state barium current was 10-30% of the initial amplitude and insensitive to intracellular cAMP.
- These characteristics resembled the steady-state calcium current observed during washout.
Conclusions:
- Two populations of calcium channels likely exist in snail neuronal membranes.
- One population appears to be dependent on cAMP metabolism.
- This cAMP-dependent population is reversibly inactivated by the passage of barium ions.