Kinetics and selectivity of a low‐voltage‐activated calcium current in chick and rat sensory neurones.

Abstract

SUMMARY1. Using the whole-cell recording mode of the patch-clamp technique, we have investigated kinetic and selectivity properties of a low-voltage-activated (l.v.a.) Ca2+ current in chick and rat dorsal root ganglion (d.r.g.) neurones.2. L.v.a currents were activated at about -50 mV and reached maximum amplitudes between -30 and -20 mV with averages of -0-16 nA in chick and -03 nA in rat d.r.g. cells with 5 mM-extracellular Ca2+. Between -60 and -20 mV, the time to peak, tp, of this current decreased with increasing membrane depolarizations. An e-fold change of tp required a 14 mV potential change in chick and a 17 mV change in rat d.r.g. cells at 22 'C.3. Between -50 and + 20 mV inactivation of this current was fast, single exponential and voltage dependent. In rat, the time constant of inactivation, Th, was smaller and less voltage dependent than in chick.4. The amplitude of these currents increased by a factor of 5-10, when the extracellular Ca2+ concentration was changed from 1 to 95 mm. Amplitudes and kinetic parameters of the currents showed typical shifts along the voltage axis. No correlation between Ca2+ current amplitudes and activation-inactivation kinetics was found, suggesting that the reaction rates which control these processes are not dependent on Ca2+ entry. Recovery from inactivation was voltage dependent and developed with a timeconstant, Tr' in the order of 1 s. Tr was nearly halved by changing the potential from -80 to -120 mV.6. Tail currents associated with membrane repolarization were also voltage dependent and developed exponentially. Their time constant decreased by a factor of 3 when the potential was changed from -60 to -100 mV.7. A second and more prominent Ca2+ current was activated at potentials positive to -20 mV h.v.a.), masking the time course of l.v.a. currents. Between -20 and 0 mV, time to peak of the entire current increased by a factor of 2 but decreased again at higher membrane potentials. Inactivation also became significantly slower in this potential range.8. The contribution of the h.v.a. component to the total membrane current was

Membrane currents in taste cells of the rat fungiform papilla. Evidence for two types of Ca currents and inhibition of K currents by saccharin.

“…The current density oflCa L of 15 pA/pF in 10 mM Ca was smaller than the current density measured in Necturus taste cells (32 pA/pF in 10 mM Ca; or in adrenal chromaffin cells (33 pA/pF in 5 mM Ca; Fenwick et al, 1982b) but similar to the density found in pancreatic /3 cells (12 pA/pF in 10 mM Ca; Rorsman and Trube, 1986). /Ca T represented only 25% of the current density of/Ca L (measured in Ca), a value typically observed for other cells (Bossu et al, 1985;Fedulova et al, 1985;Carbone and Lux, 1987;Fox et al, 1987).…”

Calcium currents in pyramidal CA1 neurons in vitro after kindling epileptogenesis in the hippocampus of the rat

“…48 An important calcium current with properties well suited to control excitability is the low-voltageactivated (LVA) current. 5,16 Until now, this current could not be detected in dissociated neurons of adult animals. We showed recently 21 that the in situ patchclamp technique in the slice allows the detection of LVA currents.…”

Electrophysiological studies of the GABAA receptor ligand, 4‐PIOL, on cultured hippocampal neurones

“…These were premixed at the required concentration by diluting stock solutions in ABSS. The solutions were applied in the vicinity (about 100pm) of the recorded neurone from a multi-barrelled perfusion pipette constructed from 7 hypodermic syringe needles (Carbone & Lux, 1987 …”