A calcium-activated, nonselective cationic conductance in Aplysia silent neurons

Dynamics of intrinsic electrophysiological properties in spinal cord neurones

The spinal cord is engaged in a wide variety of functions including generation of motor acts, coding of sensory information and autonomic control. The intrinsic electrophysiological properties of spinal neurones represent a fundamental building block of the spinal circuits executing these tasks. The intrinsic response properties of spinal neurones--determined by the particular set and distribution of voltage sensitive channels and their dynamic non-linear interactions--show a high degree of functional specialisation as reflected by the differences of intrinsic response patterns in different cell types. Specialised, cell specific electrophysiological phenotypes gradually differentiate during development and are continuously adjusted in the adult animal by metabotropic synaptic interactions and activity-dependent plasticity to meet a broad range of functional demands.

Calcium-activated non-selective channels in the nervous system

In the decade, since the first description of calcium-activated non-selective (CAN) channels in cardiac myocytes, pancreatic acini and neuroblastoma, this type of channel has been shown to have a ubiquitous distribution across a variety of tissues. Recently, their role in the function of cells of the nervous system has become better delineated. Because CAN channels pass depolarizing current, respond to cytoplasmic Ca2+ activity and do not inactivate, they are capable of producing maintained depolarization of neurons. This property endows upon CAN channels an important role in both physiological functions and pathological processes of the nervous system.

Activation of a non-specific cation conductance by intracellular injection of inositol 1,3,4,5-tetrakisphosphate into identified neurons of Aplysia

The ionic mechanism of the effect of intracellularly injected inositol 1,3,4,5-tetrakisphosphate (IP4) on the membrane of identified neurons (R9-R12) of Aplysia kurodai was investigated with conventional voltage-clamp, pressure injection, and ion-substitution techniques. Intracellular injection of IP4 into a neuron voltage-clamped at -45 mV reproducibly induced a slow inward current (20-60 s in duration, 3-5 nA in amplitude) associated with a conductance increase. The current was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential was -21 mV. The IP4-induced inward current was sensitive to changes in the external Na+, Ca2+ and K+ concentration but not to changes in Cl- concentration, and was resistant to tetrodotoxin (50 microM). When the cell was perfused with tetraethylammonium (5 mM) but not with 4-aminopyridine (5 mM), the IP4-induced inward current recorded at -45 mV slightly increased. The IP4-induced inward current was partially reduced by calcium channel blockers (Co2+ and Mn2+). These results suggest that intracellularly injected IP4 can activate a non-specific cation conductance.

Intracellularly injected inositol 1,3,4,5,6-pentakisphosphate induces a slow inward current in identified neurons of Aplysia kurodai

Micropressure injection of inositol 1,3,4,5,6-pentakisphosphate (IP5) into identified neurons (R9-R12) of Aplysia induced a slow inward current associated with a conductance increase. The IP5-induced inward current was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential of the current was -11 mV. The IP5-induced inward current was sensitive to changes in [Na+]o, [Ca2+]o and [K+]o but not to changes in [C1-]o, and was resistant to tetrodotoxin. The current was not completely abolished by Ca2+ channel blocking cations, Co2+ and Mn2+. Ion substitution and pharmacological experiments suggest that microinjection of IP5 can activate a non-specific cation conductance in Aplysia neurons.