Guinea pig visceral C-fiber neurons are diverse with respect to the K+ currents involved in action-potential repolarization.

1. Intracellular recordings were made from C-fiber neurons identified by antidromic conduction velocity in intact guinea pig nodose ganglia maintained in vitro, and whole-cell patch clamp recordings were made from dissociated guinea pig nodose neurons to investigate the contribution of various K+ conductances to action-potential repolarization. 2. The repolarizing phase of the intracellularly recorded action potential was prolonged in a concentration-dependent manner by charybdotoxin (Chtx; EC50 = 39 nM) or iberiatoxin (Ibtx; EC50 = 48 nM) in a subpopulation of 16/36 C-fiber neurons. In a subset of these experiments, removal of extracellular Ca2+ reversibly prolonged action-potential duration (APD) in the same 4/9 intracellularly recorded C-fiber neurons affected by Chtx (> or = 100 nM). These convergent results support that a Ca(2+)-activated K+ current (IC) contributes to action-potential repolarization in a restricted subpopulation of C-fiber neurons. 3. Tetraethylammonium (TEA; 1-10 mM) increased APD considerably further in the presence of 100-250 nM Chtx or Ibtx, or in nominally Ca(2+)-free superfusate in 14/14 intracellularly recorded C-fiber neurons. TEA affected APD similarly in subpopulations of neurons with and without IC, suggesting that a voltage-dependent K+ current (IK) contributes significantly to action-potential repolarization in most nodose C-fiber neurons. 4. Substitution of Mn2+ for Ca2+ reduced outward whole-cell currents elicited by voltage command steps positive to -30 mV (2-25 ms) in a subpopulation of 21/36 dissociated nodose neurons, supporting the heterogeneous expression of IC. The kinetics of outward tail current relaxations (tau s of 1.5-2 ms) measured at the return of 2-3 ms depolarizing steps to -40 mV were indistinguishable in neurons with and without IC, precluding a separation of the nodose IC and IK by a difference in deactivation rates. 5. Chtx (10-250 nM) reduced in a subpopulation of 3/8 C-fiber neurons the total outward current elicited by voltage steps depolarized to -30 mV in single microelectrode voltage-clamp recordings. TEA (5-10 mM) further reduced outward current in the presence of 100-250 nM Chtx in all eight experiments. The Chtx-sensitive current was taken to represent IC, and the TEA-sensitive current, the IK component contributing to action-potential repolarization. 6. Rapidly inactivating current (IA) was implicated in action-potential repolarization in a subpopulation of intracellularly recorded C-fiber neurons. In 4/7 neurons, incremented hyperpolarizing prepulses negative to -50 mV progressively shortened APD.(ABSTRACT TRUNCATED AT 400 WORDS)

A retrograde labeling technique for the functional study of airway-specific visceral afferent neurons.

The development of a method is described whereby primary afferent neurons that specifically innervate the airways in the guinea pig can be retrogradely labeled, acutely dissociated and studied functionally with electrophysiological techniques. Following administration of either dextran-tetramethylrhodamine, Fast Blue, or Fluorogold dye into the tracheal lumen, dye-labeled neurons can be visualized in 100 microns serial nodose ganglion sections. Control experiments show that labeling does not result from the undesirable spread of the dyes to target innervation fields in the gastrointestinal (GI) or cardiovascular (CV) systems. Neuronal somata retain dye label when acutely dissociated. Microelectrode studies provide evidence that the presence of the Rhodamine dye label and its fluorescent excitation neither alter basic electrophysiological membrane parameters nor the chemoreceptive properties of isolated neurons. Thus this new method will allow the isolation of individual airway-specific primary visceral afferent neurons for functional studies with multidisciplinary techniques.

[3H]DTG and [3H](+)-3-PPP label pharmacologically distinct sigma binding sites in guinea pig brain membranes.

The interaction of various compounds with sigma binding sites was examined in membranes prepared from whole guinea pig brain. Whereas [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine labeled a single population of binding sites exhibiting a Kd of 43 nM, [3H]1,3-di-o-tolylguanidine bound to two sites having Kds of 35 and 212 nM, and to a greater maximum number of sites than [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine. Haloperidol, 1,3-di-o-tolylguanidine, BMY 14802, and (-)-pentazocine each displayed nearly equal affinity for binding sites labeled by [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and [3H]1,3-di-o-tolylguanidine, whereas (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine was 3 times more potent in inhibiting [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine than [3H]1,3-di-o-tolylguanidine binding. In contrast, (+)-SKF 10,047, (+)-cyclazocine and (+)-pentazocine exhibited more than 9-fold higher affinity for [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine than [3H]1,3-di-o-tolylguanidine binding sites. Dextromethorphan was 15-fold more potent against [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine than [3H]1,3-di-o-tolylguanidine, inhibited [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine binding in a biphasic manner, and inhibited [3H]haloperidol and [3H](+)-SKF 10,047 binding with potencies similar to those obtained against [3H]1,3-di-o-tolylguanidine and [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine, respectively. Phenytoin increased [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and [3H](+)-SKF 10,047 binding, but did not enhance [3H]1,3-di-o-tolylguanidine or [3H]haloperidol binding. However, the potency of dextromethorphan to inhibit [3H]1,3-di-o-tolylguanidine binding was increased in the presence of phenytoin.(ABSTRACT TRUNCATED AT 250 WORDS)