Alteration of calcium conductances and outward current by cyclic adenosine monophosphate (cAMP) in neurons ofLimax maximus |
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Authors: | Philip Hockberger John A Connor |
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Institution: | 1. Department of Molecular Biophysics, AT&T Bell Laboratories, 07974, Murray Hill, New Jersey, USA 2. Department of Physiology and Biophysics, University of Illinois, 61801, Urbana, Illinois, USA
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Abstract: | Membrane responses to cyclic adenosine monophosphate (cAMP) injections have been studied by means of voltage clamp, Ca-indicator dye, and ion substitution techniques in identified neurons from the abdominal ganglion of Limax maximus. The ventral abdominal giant cell (AGC) displayed a response consisting of a decrease in outward current usually accompanied by a smaller enhancement of voltage-gated Ca2+ influx. Both responses were eliminated by external Cd2+ or Mn2+ and required membrane voltages more positive than -40 mV for expression. The enhanced influx persisted in Ba2+-substituted saline, while the decrease in outward current was blocked. A group of dorsal neurons (RD1-3, LD1) showed a mixed Na-Ca influx induced by cAMP that could be activated over a wide range of membrane potentials (less than -100 to greater than -20 mV). This flux caused a measurable increase in internal Ca2+. The influx was insensitive to Cd2+ and Mn2+ but was reduced by prolonged exposure to Co2+. The relative magnitude of the Na-Ca flux ratio showed considerable variation between specimens. In immature animals the Ca component was absent. The results demonstrated that elevation of intracellular cAMP can cause cell-specific changes of membrane conductance within closely associated neurons. |
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