Characterization of Voltage-sensitive Na+ and K+ Currents Recorded from Acutely Dissociated Pelvic Ganglion Neurons of the Adult Rat. YOSHIMURA, NAOKI AND WILLIAM C. DE GROAT. Department of Pharmacology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261 and Section of Electrophysiology, Laboratory of Physiologic and Pharmacologic Studies, National Institute on Alcohol and Alcoholism, Rockville, MD 20892.
APStracts 3:0085N, 1996.
1. Electrophysiological properties of acutely dissociated neurons from the major pelvic ganglion (MPG) of the adult male rat were studied with whole-cell patch-clamp recording techniques. The MPG neurons innervating the urinary bladder were labeled by retrograde axonal tracing methods using a fluorescent dye, Fast Blue (FB) injected into the bladder wall and identified with a fluorescent microscope. 2. Passive and active membrane properties such as resting membrane potential, input resistance, duration of action potentials, thresholds for spike activation or duration of after-hyperpolarization in unidentified MPG neurons were comparable to those of Fast Blue (FB)-labeled neurons innervating the urinary bladder. The action potential in both unidentified and bladder efferent MPG neurons was reversibly abolished by tetrodotoxin (TTX, 1 M). The after-hyperpolarization of the TTX-sensitive action potential in both groups was reduced by an application of Cd2+ (0.1 mM), and further suppressed by TEA (10 mM). Extracellularly applied TEA increased the duration of the action potential, and 4-aminopyridine (4-AP, 1 or 2 mM) also reduced the spike after-hyperpolarization and increased the spike duration. The duration of the action potential was decreased and the rate of spike repolarization was increased by approximately 2.5-fold with negative shift of membrane potential from -40 to -80 mV. 3. The isolated Na+ current was reversibly blocked by 1 M TTX and had a mean peak amplitude of 127.3 pA/pF when activated from the holding potential of -70 mV in the external solution containing 100 mM Na+. The Na+ conductance reached half- maximal activation at the membrane potential of -21.5 mV with the slope factor of 4.9 mV. The steady-state inactivation of Na+ conductance occurred at membrane potentials more depolarized than -90 mV, and the half-maximal inactivation was obtained at -57.5 mV with the slope factor of 8.8 mV. 4. The fast-transient IA current was activated at membrane potentials more depolarized than -60 mV from the holding membrane potential of -100 mV and reached a peak amplitude within 10 ms after the onset of depolarizing voltage steps, and decayed within 20-30 ms at membrane potential depolarizations to +20 to +30 mV . The IA current activated by a voltage step to +20 mV from the holding potential of -100 mV averaged 102.1 pA/pF. The half-maximal activation of the IA conductance was obtained at the membrane potential of -21.2 mV with the slope factor of 9.9 mV. In steady-state inactivation of IA current, the half-maximal inactivation occurred at -76.5 mV and the slope factor was 8.0 mV. 5. The delayed K+ current was reduced by 25-35 % by the bath application of Cd2+ or the elimination of extracellular Ca2+ ions. The bath application of 4-AP (2 mM) suppressed the IA current by 75 % and the delayed K+ current by 60 %. Extracellularly applied TEA (10 mM) suppressed the delayed K+ current by 90 %, but the IA current by only 16 % . 6. These results indicate that bladder neurons and unidentified neurons in the MPG have similar properties including a TTX-sensitive Na+ current and three distinct types of voltage-sensitive K+ currents; IA current, Ca2+-activating K+ current and delayed rectifier K+ current, which contribute to the repolarization phase of the action potential. These electrical properties of the MPG neurons resemble those of sympathetic neurons in the superior cervical and inferior mesenteric ganglia.

Received 21 September 1995; accepted in final form 23 April 1996.
APS Manuscript Number J631-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 May 96