Direct Measurements of the Effects of Cyclic Adenosine Monophosphate, and Related Compounds, on Membrane Conductances, Intracellular Calcium and Ph in Gastropod Neurons (cyclic-Amp)
Hockberger, Philip Edward
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https://hdl.handle.net/2142/77668
Description
Title
Direct Measurements of the Effects of Cyclic Adenosine Monophosphate, and Related Compounds, on Membrane Conductances, Intracellular Calcium and Ph in Gastropod Neurons (cyclic-Amp)
Author(s)
Hockberger, Philip Edward
Issue Date
1982
Department of Study
Center for Biophysics and Computational Biology
Discipline
Biophysics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biophysics, General
Language
eng
Abstract
The dose-dependent effects of intracellular injections of cyclic adenosine monophosphate (AMP) and related compounds were examined in identifiable gastropod neurons. Injecting cyclic AMP (or cyclic GMP) in amounts which should have elevated the internal concentration from 0.1-7.6 mM (mean = 3.3 mM) resulted in transient depolarizations of the cells lasting several minutes. These injections induced a transient increase in the resting sodium permeability of the neurons. Larger doses (mean = 9.0 mM) resulted in sustained depolarizations which sometimes developed into a slow-bursting firing pattern. The sustained depolarization was the result of a long-lasting increase in the net inward current underlying the negative slope resistance (NSR) region of the I-V curves in these neurons. The internal pH routinely decreased in a reversible, dose-dependent manner following cyclic AMP injections, with the peak pH responses always occurring subsequent to the peak depolarizations. Addition of the phosphodiesterase (PDE) inhibitor IBMX in the bath before injection of cyclic AMP caused a significant elevation and prolongation of both the current and pH responses. Injecting cyclic AMP analogs which are not readily hydrolized in cells also resulted in long-lasting current and pH responses. Blocking the current response by removing external sodium did not prevent the pH response. Multiwavelength measurements of arsenazo III during cyclic AMP injections into voltage clamped cells showed no changes in resting {Ca('2+)} nor in the characteristics of Ca influx or regulation during electrical activity. These results have led to the following conclusions: (1) a relatively large dose of cyclic AMP was needed to induce a depolarization, presumably due to high PDE activity in situ; (2) short as well as long-lasting changes in membrane conductances were induced by cyclic AMP injections; (3) injection led to an intracellular acidification which was not coupled to the depolarization; and (4) other than through inducing action potentials, cyclic AMP did not change the levels of intracellular free calcium.
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