Synaptic modulation of calcium‐dependent potassium conductance in myenteric neurones in the guinea‐pig.

Publisher Website
Google Scholar
Abstract
Ganglion cells of the myenteric plexus of the guinea-pig small intestine were studied with intracellular recording methods. Electrical stimulation of the interganglionic connectives elicted slow synaptic excitation (slow e.p.s.p.) associated with an increase in the input resistance of the cell. The slow e.p.s.p. continued for several seconds after termination of stimulation; they occurred only in neurons where prolonged hyperpolarizing after-potentials followed an action potential. Superfusion of the neurons with solutions containing 1-5 mM-Mn2+ or 16 mM-Mg2+ and 1 mM-Ca2+ mimicked the slow e.p.s.p. The common characteristics of Mn2+, Mg2+ and the slow e.p.s.p. were depolarization of the membrane potential, increased input resistance of the cell, augmented excitability, blockade of post-pike hyperpolarizing potentials and reversal potential between -70 and -75 mW. Analyses based on the constant field equation implied the permeability ratios of K+ to other permeant ionic species were reduced when Ca2+ influx was blocked by Mn2+ or Mg2+. The organic Ca antagonist D-600 [methoxy verapamil did not affect the neurons. Slow synaptic modulation of excitability within the myenteric plexus apparently involves a reduction of resting GK [conductance for K+] and post-spike GK which is secondary to suppression of Ca2+ influx by the neurotransmitter for the slow e.p.s.p.