Active and passive membrane properties of rat sympathetic preganglionic neurones innervating the adrenal medulla.
The intravascular release of adrenal catecholamines is a fundamental homeostatic process mediated via thoracolumbar spinal sympathetic preganglionic neurones (AD-SPN). To understand mechanisms regulating their excitability, whole-cell patch-clamp recordings were obtained from 54 retrogradely labelled neonatal rat AD-SPN. Passive membrane properties included a mean resting membrane potential, input resistance and time constant of -62 +/- 6 mV, 410 +/- 241 MOmega and 104 +/- 53 ms, respectively. AD-SPN were homogeneous with respect to their active membrane properties. These active conductances included transient outward rectification, observed as a delayed return to rest at the offset of the membrane response to hyperpolarising current pulses, with two components: a fast 4-AP-sensitive component (A-type conductance), contributing to the after-hyperpolarisation (AHP) and spike repolarisation; a slower prolonged Ba(2+)-sensitive component (D-like conductance). All AD-SPN expressed a Ba(2+)-sensitive instantaneous inwardly rectifying conductance activated at membrane potentials more negative than around -80 mV. A potassium-mediated, voltage-dependent sustained outward rectification activated at membrane potentials between -35 and -15 mV featured an atypical pharmacology with a component blocked by quinine, reduced by low extracellular pH and arachidonic acid, but lacking sensitivity to Ba(2+), TEA and intracellular Cs(+). This quinine-sensitive outward rectification contributes to spike repolarisation. Following block of potassium conductances by Cs(+) loading, AD-SPN revealed the capability for autorhythmicity and burst firing, mediated by a T-type Ca(2+) conductance. These data suggest the output capability is dynamic and diverse, and that the range of intrinsic membrane conductances expressed endow AD-SPN with the ability to generate differential and complex patterns of activity. The diversity of intrinsic membrane properties expressed by AD-SPN may be key determinants of neurotransmitter release from SPN innervating the adrenal medulla. However, factors other than active membrane conductances of AD-SPN must ultimately regulate the differential ratio of noradrenaline (NA) versus adrenaline (A) release secreted in response to various physiological and environmental demands.
Wilson
Jennifer M M
JM
Neurosciences, Ottawa Health Research Institute, University of Ottawa, Ontario, Canada K1Y 4E9, UK.
Coderre
Elaine
E
Renaud
Leo P
LP
Spanswick
David
D
D000313:Adrenal Medulla / Q000294:innervation*; D000818:Animals; D000831:Animals, Newborn; D001339:Autonomic Fibers, Preganglionic / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D004594:Electrophysiology; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D013904:Thoracic Vertebrae
D026902:Potassium Channel Blockers; D002118:Calcium